St. Mark’s Episcopal Church

Hoosick Falls, New York

 An examination, assessment and preservation plan for the exterior envelope of the structure

Prepared by Ward Hamilton

April 22, 2011

INTRODUCTION

This building conditions assessment report is an examination, assessment and preservation plan for the exterior envelope of St. Mark’s Episcopal Church located at 70 Main Street in Hoosick Falls, New York. Architect Henry Dudley designed it according to the Ecclesiological principles of Episcopal church design, after English country parish churches, which they held to be the ideal for churches of that denomination. Uncharacteristically, he used brick rather than stone. He was probably commissioned by local industrial magnate Walter A. Wood, a member of the church.  Several additions and renovations were made to the original building in the decades after its construction, most notably a parish hall in the early 20th century. In 2000 it was listed on the National Register of Historic Places.

BUILDING

The church is on a small lot on the west side of Main Street, just south of a village park and a short distance from the post office opposite. It is two blocks south of downtown. It is on a small flat lot, set back slightly with a hedge and lawn in front and mature trees around it. A driveway on the south leads to a small parking lot in the rear. Behind it is the only section of a cast iron fence that once surrounded the entire property.  There are three sections to the building itself: the nave, a freestanding bell tower with hyphen connecting it to the nave, and a parish house attached on the south. The first two are brick while the third is stucco over wood frame. The nave has a steeply pitched gable roof shingled in slate. It has corner buttresses. Its west (front) facade has a small enclosed porch with a similar roof and buttresses. Two lancet windows are on either side; a rose window is above. A shallow molded cornice is at the roofline; two ornamental brackets are at the peak. The main entrance has double wood doors with wrought iron decorative hinges and a pointed arch limestone surround.

On the sides sympathetic later enlargements have covered the original walls. Two lancet windows remain on the south, and there are roof dormers on either side. The north side’s addition, which allowed for a side aisle in the sanctuary, has paired lancets and a shed roof. A transept with lancets and a steep roof similar to the church’s main block is at the rear. The one-and-a-half-story parish hall projects from the south. It also has a steep gabled roof, and is decorated with hood moldings on the windows.   Narrow lancets also light the single-story connector to the bell tower. It has four stages, all delineated by sandstone trim. Corner buttresses rise two stories. The first has an entrance similar to the front. The second has another lancet on the east and west, the third a clock and the fourth a pointed arch louvered opening with Meneely chimes. The hipped roof is pierced by triangular vents and topped by a cross.

Inside, the sanctuary has a hammer beam roof with trusses of dark stained wood. Plaster walls, original pews, a lectern with brass eagle and stained glass from different periods complete the trim. In the chancel are a marble altar originally from another church and an elaborate oak reredos.

HISTORY

The St. Mark’s parish was founded in 1833. It held services first in the local schoolhouse, then in a meetinghouse where the village’s Baptist Church is now. Two decades after its founding, it had a congregation big enough to build its own church.  Walter A. Wood, later to become the village’s major industrialist through the manufacture of mechanical mowers and reapers, played a major part in building the church. He visited Troy, the county seat, frequently and was familiar with Henry Dudley’s work there, such as St. John’s Episcopal Church (now a contributing property to the Central Troy Historic District) and some of the buildings at Oakwood Cemetery. Dudley also designed and built Wood’s Tudor Revival house (no longer extant) on the hillside behind the church.

Dudley, an English immigrant, was a member of the New York Ecclesiological Society. Its members advocated that Episcopal churches be modeled on English country parish churches, particularly in small country towns, where they felt that form was more harmonious with the surrounding rural landscape than the white frame Greek Revival churches that had dominated American church architecture at the time. They also called for simplicity, since it was not necessary for a church to be elaborately decorated to fulfill its purpose. Most churches designed by Ecclesiologists thus featured steeply pitched roofs, axial plans, and clearly defined separations between the various functional spaces.

The only unusual aspect of St. Mark’s among Dudley’s work is its use of brick rather than stone. It is not known why, although perhaps that material was available in enough quantity in Hoosick Falls at the time to make it economical to build the church of it. Construction began on the main block in 1858; it was completed and consecrated two years later. Dudley designed the later additions, the north aisle and transept, in 1865. In the next two decades, the chimes would be added to the tower and the altar windows installed. The church underwent a major refurbishing in 1880 without any effect on the design. Ten years later the chancel was enlarged.

The last significant addition was the construction of the parish hall, in 1912–13, almost 20 years after Dudley’s death. Its original large single hall on the first floor was divided into classrooms in the mid-20th century. Since then the church has remained largely unchanged.

OVERVIEW OF EXISTING CONDITIONS

The exterior of the building was examined specific to slate, metal and other roofing, brick masonry façade and limestone foundation, and carpentry to include (but not limited to) windows, doors, trim, fascia, and soffit.   Recommendations for remedial action will follow in a later section.

Roofing

The slate is a semi-weathering, purple stone quarried in Vermont and in very good condition.  Many repairs have been made using Vermont “Sea Green” slate which is fine structurally and only impacts the aesthetics of the roof.  The flashing details, with two exceptions, are in very poor condition.  The various flashings are a combination of terne-coated steel, or some other ferrous metal, and copper; all are long past the end of their service life.  Only two valleys (replaced in recent years) are found in an acceptable condition.  Of major concern is the lack of counter-flashing over the step-flashing that makes up the sidewall details.  Of equal concern is the area where several sections of roof collect and funnel snow through a four foot opening.  Desperate attempts to correct problems are evidenced by the rubber membrane draped over the roof deck.

Masonry

The foundation/watertable is comprised of locally quarried dolomite, a marble-like limestone.  The orangey-red, common brick of the exterior is, overall, in good condition.  However, at several locations, the grade is much higher than at original construction.  This brings the problem of capillary action (“rising damp”) into play.  Many brick have deteriorated and spalled; replacement of these units is now necessary.  A general lack of maintenance (repointing, removal of vegetation, etc.) has affected, or now threatens to compromise, the integrity of several corners and pilasters.   

Carpentry, doors and windows

The wood work is found in good condition.  The stained glass windows and trefoil in the oculus have been protected with plexi-glass sheeting.  Woodwork, trim and doors appear to have been maintained well. 

RECOMMENDATIONS FOR REMEDIAL ACTION

All practices and methodologies recommended are in strict compliance with guidelines set forth by the National Park Service, US Department of the Interior[1].  On a municipal level, many communities maintain a level of vigilance specific to homes and buildings in historic neighborhoods.  The courses of action outlined, below, will address these issues in an appropriate manner.

Roofing

The slate roof is in good overall condition, but still needs hundreds of repairs performed.  All replacement units shall be matching, Vermont semi-weathering purple units.  All flashing details should be replaced with new 20 oz/sq’ copper to code and standards set by the National Slate Association.  Flashing details are identified as 163 linear feet of valleys, 98 linear feet of side-wall flashing, 233 linear feet of ridge detail, 18 linear feet of gutter to be covered with copper sheet metal, and the flashing/counter-flashing where the chimney meets the roof.  Additionally, the “four foot valley” should be replaced with approximately 140 square feet of flat-lock seamed, 20 oz/sq’ copper sheet metal roofing, installed to SMACNA standards and guidelines.  The former gutter at the eaves of roof section “Z” should be covered with 20 oz/sq’ copper sheet metal roofing, installed to SMACNA standards and guidelines. 

Masonry

Before any work takes place, the grade must be cut back and lowered below the watertable.  Brick masonry mortar joints should be repointed, as needed, with a high lime mortar that is sympathetic in texture and appearance to the rest of the building.  Absolutely no Portland cement should be used in the mix.  In the locations where replacement units are needed, those brick should come from locations on the building not visible to passers-by.  Closely matching units should then be used to fill salvage locations.  In some locations, stone elements will need to be reset.  This work, like the brick, must be performed with a high lime mortar that is sympathetic in texture and appearance to the rest of the building.  Absolutely no Portland cement should be used in the mix.

Carpentry, doors and windows

As a matter of maintenance, wood, trim and doors should be painted as needed.  No specific sections need attention at this time.  However, these elements should be monitored and scraped and painted as needed.  Note that this evaluation was performed from the ground.  Dormers on the roof above the sanctuary and the tower should be inspected with an aerial boom lift.  Maintenance issues should be addresses at that time.

ENGINEERING ESTIMATE OF COST FOR PRESERVATION WORK

The following estimates of cost assume that a fully-insured, experienced preservation contractor performs the tasks specified at full commercial rate.  The prices do not assume work performed at prevailing wage.  Prevailing wages are the rates charged by union-shop contractors, and will result in a higher price than the estimates provided. 

Roofing

(a)  Replace 163 linear feet of open valley details … $48,560

(b)  Replace 98 linear feet of sidewall flashing detail … $26,130

(c)  Replace flashing and counter-flashing detail, chimney … $4650

(d)  Inspect and repair slate, as needed, entire slate roof … $14,840

(e)  Install approx. 140 square feet of flat-lock copper roofing … $19,280

(f)  Cover 18 linear feet of gutters with copper sheet metal … $7200

(g)  Replace 233 linear feet of copper ridge detail … $18,660

Masonry

(a)  Replace broken, spalled, and missing brick; repoint brick, as needed, with high lime mortar, entire exterior … $26,220

(b)  Reset stone watertable pieces, as needed, above grade … $12,600

(c)  Alterations to grade, invasive vegetation removed … $5400

Carpentry, doors and windows

(a)  Set aside funds for inspection of wood work with aerial boom lift and attention to same … $7680

PRIORITIZATION OF PRESERVATION TASKS

All tasks, above, are listed from greatest to least importance below.  Certainly, the issue of water infiltration is of paramount concern:

1. Install approx. 140 square feet of flat-lock copper roofing
2. Alterations to grade, invasive vegetation removed
3. Replace broken, spalled, and missing brick; repoint brick, as needed, with high lime mortar, entire exterior
4. Reset stone watertable pieces, as needed, above grade
5. Replace 163 linear feet of open valley details
6. Replace 98 linear feet of sidewall flashing detail
7. Replace flashing and counter-flashing detail, chimney
8. Inspect and repair slate, as needed, entire slate roof
9. Cover 18 linear feet of gutters with copper sheet metal
10. Replace 233 linear feet of copper ridge detail
11. Set aside funds for inspection of wood work with aerial boom lift and some attention to same

CONCLUSION

Upon careful examination of the exterior envelope of this structure, the primary concerns are water infiltration and the effect of the rising grade.  Precipitation entering through the roofing system will become the cause of many other problems and system failures.  As such, remedial action starts with the roof.  Masonry issues, however, are of equal concern and should not be ignored.  The moderate-sized repairs that are needed now will only grow with time.  The primary goals are to stop water infiltration and correct masonry failures.  Once this is achieved, and even while work is on-going, regular inspection and maintenance of the building systems is critical to the structure’s longevity.  Be sure to have the roofing inspected annually, gutters and outlets cleaned out biannually, and vegetation removed from the building (including the grade, vines and other vegetation) as needed.

CREDIT

Details specific to the description of this structure and its architectural history were taken directly from “National Register of Historic Places nomination, St. Mark’s Episcopal Church,” Peter Shaver, New York State Office of Parks, Recreation and Historic Preservation. (November 24, 1999)

 APPENDIX – Photographic Documentation

 The base of this pilaster is sheering from the structure.  Failure to address appropriately will result in major structural problems.

Poorly executed slate repairs (typ. throughout the field of the roof)

Again, a lack of maintenance, invasive vines, and the changes in grade are gradually compromising the structural integrity of the corner of the building

 Another view of the “valley” where two steeply-pitched sections of roof (one an 18:12, the other a 20:12) dump over 500 square feet of collected snow onto a lower-sloped section (8:12.)  Compounding the problem are the steep sections, seen above

  Poor planning:  Snow that lands on over 660 square feet of roofing in this area is funneled into this four foot opening.  Inappropriate attempts to address problems include rubber membranes, as seen here

A general lack of maintenance is contributing to major issues.  Failure to repoint the brick masonry of this pilaster may compromise its structural integrity

A complex situation:  Various planes of the roof, each at different angles, converge.  Flashing details at these intersections are more involved and, in this instance, compounded by a chimney protrusion

Sheet metal flashings are a combination of copper and terne-coated steel or similar, ferrous sheet metal.  All have outlived their service life and need replacement.  Slate at the bases of the valleys is in poor condition (typical at several locations)

Changes in grade are bringing moisture to the brick.  The stones of the watertable, which act as a damp-proofing course, become obsolete in situations like this.  Through capillary action, moisture rises into the brick and causes deterioration

None of the sidewall flashing details are counter-flashed.  Instead tar and mastic has been used to stop precipitation from infiltrating the building.  Some makeshift flashing modifications, as seen here, are found at other locations as well

Basic Framing Techniques and Theory

The whole unit represented in a complete timber frame may be broken-down into three subsections in order to better understand their intra/inter-workings: 1) the floor frame, 2) the wall frame and 3) the roof/ceiling frame. The floor frame is a combination of “[…] posts, beams, sill plates, joists and subfloor” (Anderson, 2002, pg. 19). The components that comprise the floor frame are arranged in order to reduce the amount of shrinkage and settling of the wall and roof frames. Said movements are owed to internal and external factors: the moisture content of the wood combined with the stresses and strains inherent in a frame, and the external forces of nature and living to which a frame is exposed. Post and beam meet at a 90 degree angle at the ends of the structure providing a horizontal base and vertical extension. The beams are crossected by joists which provide lateral support and stiffness to the frame. The sub-floor does not provide structural support; it provides a skin for the interior flooring.
The floor frame provides a basis upon which a wall frame can be constructed. Anderson recommends the following wood-types for use in wall frames: Douglas-fir, hemlocks, southern pine, spruce and white fir. The reasons he gives for these specifications are “[…] good stiffness, freedom from warp, good nail-holding ability and ease of working” (ibid, pg. 31). The components of a wall-frame include the vertical studs and their horizontal counterparts. The former are divided into the following types: single-storey and two storey. The latter are comprised of bearers, girts, window headers/sills top plates and joists. Additionally, single-storey studs may be reinforced by diagonal braces; these braces relieve pressure between beam and post, while adding stability to the studs.

The basic form of the roof-frame in a timber frame structure, the gable roof, is composed of the following elements: rafters (extending on a diagonal axis from the top plate and terminating at the top of the frame), the ridge board (the horizontal piece which forms the top of the frame and to which the rafters are secured), the end stud (the roof version of the single/two-storey stud), collar beams (which provide lateral support between the rafters) and ceiling joists. Anderson mentions three types of gable roofs: 1) the simple and familiar triangular form described above, 2) the gable dormer—featuring a windowed-protruding form from the roof and 3) the hip—which features triangular forms in the front and back and trapezoidal forms on the sides.

Timber framing and Balloon Framing

The move away from timber framing toward balloon framing begun in the 19th century—while balloon framing is not the subject of the present paper, it does provide a helpful contrast for understanding the history, evolution and aesthetic of the timber frame. The Old-House Journal notes that “The basic difference[s] between timber and balloon framing [are] that in balloon framing every stud in the frame is a load-carrying element […] [the substitution] of mechanical fasteners (nails) for the elaborate woodwork joints (mortise and tenon, etc.)” (1980, pg. 197). Thus, the move from timber to balloon framing occurred due to economic considerations: the balloon frame used less material, took less time to construct and required a more standardized and teachable skill-set.
When the Puritans came to America and settled in what would become the 13 original colonies of the U.S. they brought with them framing techniques practiced in Europe for centuries. The tradition of European framing had been passed down through these centuries owing to the artisanal guild system, which, having been created in the middle ages, provided a transnational system of teaching and developing construction techniques. The guild system would remain in place until the Industrial Revolution (exactly the time that balloon framing overtook timber framing as the preferred method of house construction). The basic joining technique was comprised of a mortise and tenon system. The system was developed in order how to solve the fundamental problem of construction: how to join a post and beam at a 90 degree angle? The ancient Greeks had bypassed this problem with a post and lintel system; the Romans innovated with the arch; medieval Europeans developed a female/male adaptor system.
The mortar/tenon process is a manual labor-intensive process. The mortise-cavities and tenons are formed with adzes. Additionally, the means of connection vary according to the training and preference of the carpenter in question. Conversely, mechanical means of joining and producing uniform studs limited the ways in which frames could be joined. The Old House Journal notes that distinguishing between a timber and balloon frame is difficult to do from an outside perspective; however, “[…] on the inside, there are usually tell-tale signs. The posts and summer beams are so big the usually protrude from walls and ceilings […]” (ibid). The reason for the size differential is two-fold: 1) before builders had access to mechanical means of cutting wood, all of the timbers used in a frame had to be cut-down from a near-by forest then planed and measured by hand; and, 2) the weight of a timber frame structure is dispersed among the beams and posts—whereas, in a balloon frame structure the load is spread evenly among the studs, braces, etc.

Changes in Joinery Techniques

The exposed interior common to timber framed structures led early American constructors to innovate in their approaches to joining techniques. It seems clear that the exposed interior posts presented a problem because they gave houses an unfinished structure. Jan Leo Lewandoski catalogs eight types of joining methods: 1) exposed decorated, 2) cased, 3) cornered, 4) deep wall, 5) thin wall, 6) vertical plank, 7) skeleton plank and 8) balloon (1995, pg. 42). Without covering all of the individual differences it may be helpful to point out how these different techniques ‘solve’ different ‘problems’ presented by the timber frame structure. The easiest way of dealing with the problem of the exposed frame was to hand decorate it. The exposed decorated technique did not change the method of fastening; it simply altered the appearance of the exposed beam by fashioning its edges with “[…] chamfers, ovolos, and beads […]” (ibid, pg. 43).

Another technique that did not change the joining method (but only hid the exposed post) was adding casing, or draping the post with a skin that matched the walls. The cornered method simply cut-out a section of the post so that it would be plumb with the wall and the deep wall method extended the depth of the wall so that it would correspond to the thickness of the post. What each of these methods point to was the fact that there was something fundamentally disturbing to early Americans about the exposed interior. Lewandoski traces this disturbance to a shift in aesthetic sensibility: “[Early Americans] admired Greek and Roman structures [which] were built of masonry and had sharp, straight interior lines [they] sought to summon up the appearance of the masonry public buildings of the classical world in the average wooden residences of the new world” (ibid, pg. 44). Interestingly, Lewandoski implies that trends in the development of timber framing were not simply practical—they also had their origin in how they conceived of the ideal living space. Said space would not be interrupted by protruding hand-hewn posts.

Willie Graham, performing further research in the same area, examines the way that pre-industrial framing systems developed in order to deal with practical and theoretical concerns. He defines the system of pre-balloon framing in America as an example of a “vernacular” style as opposed to an industrial style (2003, pg. 179). The former represents a particular response to a specific problem of carpentry. The response is determined by the carpenter’s experience and training. The carpenter’s experience and training is determined in part by the unique conditions of his environment. Graham notes that the unique environmental conditions of the Chesapeake area were an abundance of wood and a lack of skilled labor.

Stylistic Flexibility of Timber Framing: Analysis

The flexibility of the timber framing process may be understood in further detail by examining two historical examples of its exteriors: the Bryant Cushing house in Massachusetts and Chesapeake-style house—both from the 19th century (Library of Congress, 2010, web). The Cushing house is a two-storey, rectilinear affair. Its two symmetrical halves are bisected in the middle by the entrance. Lewandowski’s point about early New Englander’s desire to emulate Greek and Roman architecture is well-taken in this example: the entrance-way is done in the Doric Greek style with a column, architrave, frieze and cornice. Additionally, the Cushing house is a fine example of a building method that stresses proportionality, regularity and simplicity. The Chesapeake house is different. It is two storeys—but, its second story is contained within a gabled and dormered roof. Its doorway and windows do not imitate any style—they seem to be simply and practically openings. The horizontally-oriented planks which cover the first-storey are irregular. If Graham’s point about the lack of carpentry skills available to Marylanders is correct, it is especially so when considering this example.

Conclusion

The structure and style of American timber framing systems up to 1900 is owed first to practical considerations and historical determinates and second to aesthetic sensibilities. Additionally, the environment in which carpenters work influenced them more 200 years ago than it does today. This is owed to factors such as standardized education, mechanization of building processes and the ability to transport materials across long distances. Despite the fact that the timber framing method was eventually overtaken by the more economical balloon framing method, it is still interesting and beneficial to examine the differences within the timber framing method. These differences speak at once to the diversity and similarity of the American building heritage.

References

Anderson, L.O. (2002) Wood – frame house construction. Washington: Books for Business.

Graham, Willie. (2003) “Preindustrial framing in the Chesapeake.” Perspectives in Vernacular Architecture, 9, 179-196.

Lewandoski, Jan Leo. (1995) ”Transitional timber framing in Vermont.” APT Bulletin, 26, 2/3, 42-50.

“Timber-frame houses in the historic American buildings survey.” (2010) The Library of Congress. Retrieved 5 December 2010, from http://www.loc.gov/rr/print/list/100_tim3.html

“Traditional house framing.” (Dec., 1980) Old House Journal, 8, 12, 197-200.

A versatile material, plaster could be applied over brick, stone, half-timber, or frame construction. It provided a durable surface that was easy to clean and that could be applied to flat or curved walls and ceilings.

Plaster could be treated in any number of ways: it could receive stenciling, decorative painting, wallpaper, or whitewash. This variety and the adaptability of the material to nearly any building size, shape, or configuration meant that plaster was the wall surface chosen for nearly all buildings until the 1930s or 40s.

Plaster was used as the interior surface coating of this elegant 1911 church located in Eugene, Oregon. Photo: NPS files.

Historic plaster may first appear so fraught with problems that its total removal seems the only alternative. But there are practical and historical reasons for saving it. First, three-coat plaster is unmatched in strength and durability. It resists fire and reduces sound transmission. Next, replacing plaster is expensive. A building owner needs to think carefully about the condition of the plaster that remains; plaster is often not as badly damaged as it first appears.

Of more concern to preservationists, however, original lime and gypsum plaster is part of the building’s historic fabric–its smooth troweled or textured surfaces and subtle contours evoke the presence of America’s earlier craftsmen. Plaster can also serve as a plain surface for irreplaceable decorative finishes. For both reasons, plaster walls and ceilings contribute to the historic character of the interior and should be left in place and repaired if at all possible. 

The approaches described in this Brief stress repairs using wet plaster, and traditional materials and techniques that will best assist the preservation of historic plaster walls and ceilings–and their appearance. Dry wall repairs are not included here, but have been written about extensively in other contexts. Finally, this Brief describes a replacement option when historic plaster cannot be repaired. Thus, a veneer plaster system is discussed rather than dry wall. Veneer systems include a coat or coats of wet plaster–although thinly applied–which can, to a greater extent, simulate traditional hand-troweled or textured finish coats. This system is generally better suited to historic preservation projects than dry wall.

To repair plaster, a building owner must often enlist the help of a plasterer. Plastering is a skilled craft, requiring years of training and special tools. While minor repairs can be undertaken by building owners, most repairs will require the assistance of a plasterer.

Historical Background

Plasterers in North America have relied on two materials to create their handiwork–lime and gypsum. Until the end of the 19th century, plasterers used lime plaster. Lime plaster was made from four ingredients: lime, aggregate, fiber, and water. The lime came from ground-and-heated limestone or oyster shells; the aggregate from sand; and the fiber from cattle or hog hair. Manufacturing changes at the end of the 19th century made it possible to use gypsum as a plastering material. Gypsum and lime plasters were used in combination for the base and finish coats during the early part of the 20th century; gypsum was eventually favored because it set more rapidly and, initially, had a harder finish.

The builders of this mid-18th century house installed the baseboard molding first, then applied a mud and horse hair plaster. Lime was used for the finish plaster. Photo: NPS files.

Not only did the basic plastering material change, but the method of application changed also. In early America, the windows, doors, and all other trim were installed before the plaster was applied to the wall. Generally the woodwork was prime-painted before plastering. Obtaining a plumb, level wall, while working against built-up moldings, must have been difficult. But sometime in the first half of the 19th century, builders began installing wooden plaster “grounds” around windows and doors and at the base of the wall. Installing these grounds so that they were level and plumb made the job much easier because the plasterer could work from a level, plumb, straight surface. Woodwork was then nailed to the “grounds” after the walls were plastered. Evidence of plaster behind trim is often an aid to dating historic houses, or to discerning their physical evolution.

Lime Plaster

When building a house, plasterers traditionally mixed bags of quick lime with water to “hydrate” or “slake” the lime. As the lime absorbed the water, heat was given off. When the heat diminished, and the lime and water were thoroughly mixed, the lime putty that resulted was used to make plaster.

When lime putty, sand, water, and animal hair were mixed, the mixture provided the plasterer with “coarse stuff.” This mixture was applied in one or two layers to build up the wall thickness. But the best plaster was done with three coats. The first two coats made up the coarse stuff; they were the scratch coat and the brown coat. The finish plaster, called “setting stuff,” contained a much higher proportion of lime putty, little aggregate, and no fiber, and gave the wall a smooth white surface finish.

Schifferstadt, a simple house of German origin that dates to 1756, utilized plaster for both flat and curved walls. The building is located in Frederick, Maryland Photo: NPS files.

Compared to the 3/8-inch-thick layers of the scratch and brown coats, the finish coat was a mere 1/8-inch thick. Additives were used for various finish qualities. For example, fine white sand was mixed in for a “float finish.” This finish was popular in the early 1900s. (If the plasterer raked the sand with a broom, the plaster wall would retain swirl marks or stipples.) Or marble dust was added to create a hard-finish white coat which could be smoothed and polished with a steel trowel. Finally, a little plaster of Paris, or “gauged stuff,” was often added to the finish plaster to accelerate the setting time.

Although lime plaster was used in this country until the early 1900s, it had certain disadvantages. A plastered wall could take more than a year to dry; this delayed painting or papering. In addition, bagged quick lime had to be carefully protected from contact with air, or it became inert because it reacted with ambient moisture and carbon dioxide. Around 1900, gypsum began to be used as a plastering material.

Gypsum Plaster

Gypsum begins to cure as soon as it is mixed with water. It sets in minutes and completely dries in two to three weeks. Historically, gypsum made a more rigid plaster and did not require a fibrous binder. However it is difficult to tell the difference between lime and gypsum plaster once the plaster has cured.

Many of these traditional plastering tools are still used today. Drawing: NPS files.

Despite these desirable working characteristics, gypsum plaster was more vulnerable to water damage than lime. Lime plasters had often been applied directly to masonry walls (without lathing), forming a suction bond. They could survive occasional wind-driven moisture or water winking up from the ground. Gypsum plaster needed protection from water. Furring strips had to be used against masonry walls to create a dead air space. This prevented moisture transfer.

In rehabilitation and restoration projects, one should rely on the plasterer’s judgment about whether to use lime or gypsum plaster. In general, gypsum plaster is the material plasterers use today. Different types of aggregate may be specified by the architect such as clean river sand, perlite, pumice, or vermiculite; however, if historic finishes and textures are being replicated, sand should be used as the base-coat aggregate. Today, if fiber is required in a base coat, a special gypsum is available which includes wood fibers. Lime putty, mixed with about 35% gypsum (gauging plaster) to help it harden, is still used as the finish coat.

Lath

Lath provided a means of holding the plaster in place. Wooden lath was nailed at right angles directly to the structural members of the buildings (the joists and studs), or it was fastened to nonstructural spaced strips known as furring strips. Three types of lath can be found on historic buildings.

Wood Lath. Wood lath is usually made up of narrow, thin strips of wood with spaces in between. The plasterer applies a slight pressure to push the wet plaster through the spaces. The plaster slumps down on the inside of the wall, forming plaster “keys.” These keys hold the plaster in place.

Metal Lath. Metal lath, patented in England in 1797, began to be used in parts of the United States toward the end of the 19th century. The steel making up the metal lath contained many more spaces than wood lath had contained. These spaces increased the number of keys; metal lath was better able to hold plaster than wood lath had been.

Rock Lath. A third lath system commonly used was rock lath (also called plaster board or gypsum-board lath). In use as early as 1900, rock lath was made up of compressed gypsum covered by a paper facing. Some rock lath was textured or perforated to provide a key for wet plaster. A special paper with gypsum crystals in it provides the key for rock lath used today; when wet plaster is applied to the surface, a crystalline bond is achieved.

Rock lath was the most economical of the three lathing systems. Lathers or carpenters could prepare a room more quickly. By the late 1930s, rock lath was used almost exclusively in residential plastering.

Common Plaster Problems

When plaster dries, it is a relatively rigid material which should last almost indefinitely. However, there are conditions that cause plaster to crack, effloresce, separate, or become detached from its lath framewor. These include:

• Structural Problems
• Poor Workmanship
• Improper Curing
• Moisture

Structural Problems

Overloading. Stresses within a wall, or acting on the house as a whole, can create stress cracks. Appearing as diagonal lines in a wall, stress cracks usually start at a door or window frame, but they can appear anywhere in the wall, with seemingly random starting points .

Builders of now-historic houses had no codes to help them size the structural members of buildings. The weight of the roof, the second and third stories, the furniture, and the occupants could impose a heavy burden on beams, joists, and studs. Even when houses were built properly, later remodeling efforts may have cut in a doorway or window without adding a structural beam or “header” across the top of the opening. Occasionally, load-bearing members were simply too small to carry the loads above them. Deflection or wood “creep” (deflection that occurs over time) can create cracks in plaster.

Stress cracks in plaster over a kitchen door frame can be repaired using fiberglass mesh tape and joint compound. Photo: NPS files.

Overloading and structural movement (especially when combined with rotting lath, rusted nails, or poor quality plaster) can cause plaster to detach from the lath. The plaster loses its key. When the mechanical bond with the lath is broken, plaster becomes loose or bowed. If repairs are not made, especially to ceilings, gravity will simply cause chunks of plaster to fall to the floor.

Settlement/Vibration. Cracks in walls can also result when houses settle. Houses built on clay soils are especially vulnerable. Many types of clay (such as montmorillonite) are highly expansive.

In the dry season, water evaporates from the clay particles, causing them to contract. During the rainy season, the clay swells. Thus, a building can be riding on an unstable footing. Diagonal cracks running in opposite directions suggest that house settling and soil conditions may be at fault. Similar symptoms occur when there is a nearby source of vibration-blasting, a train line, busy highway, or repeated sonic booms. 

Lath movement. Horizontal cracks are often caused by lath movement. Because it absorbs moisture from the air, wood lath expands and contracts as humidity rises and falls. This can cause cracks to appear year after year. Cracks can also appear between rock lath panels. A nail holding the edge of a piece of lath may rust or loosen, or structural movement in the wood framing behind the lath may cause a seam to open. Heavy loads in a storage area above a rock-lath ceiling can also cause ceiling cracks.

Errors in initial building construction such as improper bracing, poor corner construction, faulty framing of doors and windows, and undersized beams and floor joists eventually “telegraph” through to the plaster surface.

Poor Workmanship

In addition to problems caused by movement or weakness in the structural framework, plaster durability can be affected by poor materials or workmanship.

Poorly proportioned mix. The proper proportioning and mixing of materials are vital to the quality of the plaster job. A bad mix can cause problems that appear years later in a plaster wall. Until recently, proportions of aggregate and lime were mixed on the job. A plasterer may have skimped on the amount of cementing material (lime or gypsum) because sand was the cheaper material. Over sanding can cause the plaster to weaken or crumble. Plaster made from a poorly proportioned mix may be more difficult to repair.

Incompatible base coats and finish coats. Use of perlite as an aggregate also presented problems. Perlite is a lightweight aggregate used in the base coat instead of sand. It performs well in cold weather and has a slightly better insulating value. But if a smooth lime finish coat was applied over perlited base coats on wood or rock lath, cracks would appear in the finish coat and the entire job would have to be redone. To prevent this, a plasterer had to add fine silica sand or finely crushed perlite to the finish coat to compensate for the dramatically differing shrinkage rates between the base coat and the finish coat.

The smooth-trowled lime finish has delaminated from the brown coat underneath. Photo: Marylee MacDonald.

Improper plaster application. The finish coat is subject to “chip cracking” if it was applied over an excessively dry base coat, or was insufficiently troweled, or if too little gauging plaster was used. Chip cracking looks very much like an alligatored paint surface. Another common problem is called map cracking–fine, irregular cracks that occur when the finish coat has been applied to an over sanded base coat or a very thin base coat.

Too much retardant. Retarding agents are added to slow down the rate at which plaster sets, and thus inhibit hardening. They have traditionally included ammonia, glue, gelatin, starch, molasses, or vegetable oil. If the plasterer has used too much retardant, however, a gypsum plaster will not set within a normal 20 to 30 minute time period. As a result, the surface becomes soft and powdery.

Inadequate plaster thickness. Plaster is applied in three coats over wood lath and metal lath–the scratch, brown, and finish coats. In three-coat work, the scratch coat and brown coat were sometimes applied on successive days to make up the required wall thickness. Using rock lath allowed the plasterer to apply one base coat and the finish coat–a two-coat job.

If a plasterer skimped on materials, the wall may not have sufficient plaster thickness to withstand the normal stresses within a building. The minimum total thickness for plaster on gypsum board (rock lath) is 1/2 inch. On metal lath the minimum thickness is 5/8 inch; and for wood lath it is about 3/4 to 7/8 inch. This minimum plaster thickness may affect the thickness of trim projecting from the wall’s plane.

Improper Curing

Proper temperature and air circulation during curing are key factors in a durable plaster job. The ideal temperature for plaster to cure is between 55 to 70 degrees Fahrenheit. However, historic houses were sometimes plastered before window sashes were put in. There was no way to control temperature and humidity.

Dry outs, freezing, and sweat-outs. When temperatures were too hot, the plaster would return to its original condition before it was mixed with water, that is, calcined gypsum. A plasterer would have to spray the wall with alum water to reset the plaster. If freezing occurred before the plaster had set, the job would simply have to be redone. If the windows were shut so that air could not circulate, the plaster was subject to sweat-out or rot. Since there is no cure for rotted plaster, the affected area had to be removed and replastered. 

Moisture

Plaster applied to a masonry wall is vulnerable to water damage if the wall is constantly wet. When salts from the masonry substrate come in contact with water, they migrate to the surface of the plaster, appearing as dry bubbles or efflorescence. The source of the moisture must be eliminated before replastering the damaged area.

Sources of Water Damage. Moisture problems occur for several reasons. Interior plumbing leaks in older houses are common. Roofs may leak, causing ceiling damage. Gutters and downspouts may also leak, pouring rain water next to the building foundation. In brick buildings, dampness at the foundation level can wick up into the above-grade walls. Another common source of moisture is splashback. When there is a paved area next to a masonry building, rainwater splashing up from the paving can dampen masonry walls. In both cases water travels through the masonry and damages interior plaster. Coatings applied to the interior are not effective over the long run. The moisture problem must be stopped on the outside of the wall.

Repairing Historic Plaster

Many of the problems described above may not be easy to remedy. If major structural problems are found to be the source of the plaster problem, the structural problem should be corrected. Some repairs can be made by removing only small sections of plaster to gain access. Minor structural problems that will not endanger the building can generally be ignored. Cosmetic damages from minor building movement, holes, or bowed areas can be repaired without the need for wholesale demolition. However, it may be necessary to remove deteriorated plaster caused by rising damp in order for masonry walls to dry out. Repairs made to a wet base will fail again.
 

Canvassing Uneven Wall Surfaces

Uneven wall surfaces, caused by previous patching or by partial wallpaper removal, are common in old houses. As long as the plaster is generally sound, cosmetically unattractive plaster walls can be “wallpapered” with strips of a canvas or fabric-like material. Historically, canvassing covered imperfections in the plaster and provided a stable base for decorative painting or wallpaper.

Filling Cracks

Hairline cracks in wall and ceiling plaster are not a serious cause for concern as long as the underlying plaster is in good condition. They may be filled easily with a patching material. For cracks that reopen with seasonal humidity change, a slightly different method is used. First the crack is widened slightly with a sharp, pointed tool such as a crack widener or a triangular can opener. Then the crack is filled. For more persistent cracks, it may be necessary to bridge the crack with tape. In this instance, a fiberglass mesh tape is pressed into the patching material.

After the first application of a quick setting joint compound dries, a second coat is used to cover the tape, feathering it at the edges. A third coat is applied to even out the surface, followed by light sanding. The area is cleaned off with a damp sponge, then dried to remove any leftover plaster residue or dust. 

When cracks are larger and due to structural movement, repairs need to be made to the structural system before repairing the plaster. Then, the plaster on each side of the crack should be removed to a width of about 6 inches down to the lath. The debris is cleaned out, and metal lath applied to the cleared area, leaving the existing wood lath in place. The metal lath usually prevents further cracking. The crack is patched with an appropriate plaster in three layers (i.e., base coats and finish coat). If a crack seems to be expanding, a structural engineer should be consulted.

In this New Hampshire residence dating from the 1790s, the original plaster was a single coat of lime, sand, and horsehair applied over split lath. A one-coat repair, in this case, is appropriate. Photo: John Leeke.

Replacing Delaminated Areas of the Finish CoatSometimes the finish coat of plaster comes loose from the base coat. In making this type of repair, the plasterer paints a liquid plaster-bonding agent onto the areas of base-coat plaster that will be replastered with a new lime finish coat. A homeowner wishing to repair small areas of delaminated finish coat can use the methods described in “Patching Materials.”

Patching Holes in Walls

For small holes (less than 4 inches in diameter) that involve loss of the brown and finish coats, the repair is made in two applications. First, a layer of base coat plaster is troweled in place and scraped back below the level of the existing plaster. When the base coat has set but not dried, more plaster is applied to create a smooth, level surface. One-coat patching is not generally recommended by plasterers because it tends to produce concave surfaces that show up when the work is painted. Of course, if the lath only had one coat of plaster originally, then a one-coat patch is appropriate.

Flat-head wood screws and plaster washers were used to reattach loose ceiling plaster to the wood lath. After the crack is covered with fiberglass mesh tape, all will be skim-coated with a patching compound. Photo: John Obed Curtis.

 

For larger holes where all three coats of plaster are damaged or missing down to the wood lath, plasterers generally proceed along these lines. First, all the old plaster is cleaned out and any loose lath is re-nailed. Next, a water mist is sprayed on the old lath to keep it from twisting when the new, wet plaster is applied, or better still, a bonding agent is used.

To provide more reliable keying and to strengthen the patch, expanded metal lath (diamond mesh) should be attached to the wood lath with tie wires or nailed over the wood lath with lath nails. The plaster is then applied in three layers over the metal lath, lapping each new layer of plaster over the old plaster so that old and new are evenly joined. This stepping is recommended to produce a strong, invisible patch. Also, if a patch is made in a plaster wall that is slightly wavy, the contour of the patch should be made to conform to the irregularities of the existing work. A flat patch will stand out from the rest of the wall. 

Patching Holes in Ceilings

This beaded ceiling in one of the bedrooms of the 1847 Lockwood House, Harpers Ferry, West Virginia, is missing portions of plaster due to broken keys. Photo: NPS files.

 

Hairline cracks and holes may be unsightly, but when portions of the ceiling come loose, a more serious problem exists. The keys holding the plaster to the ceiling have probably broken. First, the plaster around the loose plaster should be examined.

Keys may have deteriorated because of a localized moisture problem, poor quality plaster, or structural overloading; yet, the surrounding system may be intact. If the areas surrounding the loose area are in reasonably good condition, the loose plaster can be reattached to the lath using flathead wood screws and plaster washers. To patch a hole in the ceiling plaster, metal lath is fastened over the wood lath; then the hole is filled with successive layers of plaster, as described above. 

Establishing New Plaster Keys

If the back of the ceiling lath is accessible (usually from the attic or after removing floor boards), small areas of bowed-out plaster can be pushed back against the lath. A padded piece of plywood and braces are used to secure the loose plaster. After dampening the old lath and coating the damaged area with a bonding agent, a fairly liquid plaster mix (with a glue size retardant added) is applied to the backs of the lath, and worked into the voids between the faces of the lath and the back of the plaster. While this first layer is still damp, plaster-soaked strips of jute scrim are laid across the backs of the lath and pressed firmly into the first layer as reinforcement. The original lath must be secure, otherwise the weight of the patching plaster may loosen it.

Loose, damaged plaster can also be re-keyed when the goal is to conserve decorative surfaces or wallpaper. Large areas of ceilings and walls can be saved. This method requires the assistance of a skilled conservator–it is not a repair technique used by most plasterers.

The conservator injects an acrylic adhesive mixture through holes drilled in the face of the plaster (or through the lath from behind, when accessible). The loose plaster is held firm with plywood bracing until the adhesive bonding mixture sets. When complete, gaps between the plaster and lath are filled, and the loose plaster is secure. 

When ceiling repairs are made with wet plaster or with an injected adhesive mixture, the old loose plaster must be supported with a plywood brace until re-keying is complete. Photo: John Leeke.

Replastering Over the Old Ceiling

If a historic ceiling is too cracked to patch or is sagging (but not damaged from moisture), plasterers routinely keep the old ceiling and simply relath and replaster over it. This repair technique can be used if lowering the ceiling slightly does not affect other ornamental features. The existing ceiling is covered with 1×3-inch wood furring strips, one to each joist, and fastened completely through the old lath and plaster using a screw gun. Expanded metal lath or gypsum board lath is nailed over the furring strips. Finally, two or three coats are applied according to traditional methods. Replastering over the old ceiling saves time, creates much less dust than demolition, and gives added fire protection.

When Damaged Plaster Cannot be Repaired
–Replacement Options

Partial or complete removal may be necessary if plaster is badly damaged, particularly if the damage was caused by long-term moisture problems. Workers undertaking demolition should wear OSHA-approved masks because the plaster dust that flies into the air may contain decades of coal soot. Lead, from lead based paint, is another danger. Long-sleeved clothing and head-and-eye protection should be worn. Asbestos, used in the mid-twentieth century as an insulating and fireproofing additive, may also be present and OSHA-recommended precautions should be taken. If plaster in adjacent rooms is still in good condition, walls should not be pounded–a small trowel or pry bar is worked behind the plaster carefully in order to pry loose pieces off the wall.

When the damaged plaster has been removed, the owner must decide whether to replaster over the existing lath or use a different system. This decision should be based in part on the thickness of the original plaster and the condition of the original lath. Economy and time are also valid considerations. It is important to ensure that the wood trim around the windows and doors will have the same “reveal” as before. (The “reveal” is the projection of the wood trim from the surface of the plastered wall). A lath and plaster system that will give this required depth should be selected.

Replastering–Alternative Lath Systems for New Plaster

Replastering old wood lath. When plasterers work with old lath, each lath strip is re-nailed and the chunks of old plaster are cleaned out. Because the old lath is dry, it must be thoroughly soaked before applying the base coats of plaster, or it will warp and buckle; furthermore, because the water is drawn out, the plaster will fail to set properly. As noted earlier, if new metal lath is installed over old wood lath as the base for new plaster, many of these problems can be avoided and the historic lath can be retained. The ceiling should still be sprayed unless a vapor barrier is placed behind the metal lath.

Replastering over new metal lath. An alternative to reusing the old wood lath is to install a different lathing system. Galvanized metal lath is the most expensive, but also the most reliable in terms of longevity, stability, and proper keying. When lathing over open joists, the plasterer should cover the joists with kraft paper or a polyethylene vapor barrier. Three coats of wet plaster are applied consecutively to form a solid, monolithic unit with the lath. The scratch coat keys into the metal lath; the second, or brown, coat bonds to the scratch coat and builds the thickness; the third, or finish coat, consists of lime putty and gauging plaster.

Repairs are being made to the historic plaster. Expanded metal lath is cut to fit the hole, then attached to the wood lath with a tie-wire. Two ready-mix gypsum coats are applied, then a smooth-trowled coat of gauged lime. Photo: Walter Jowers.

 

Replastering over new rock lath. It is also possible to use rock lath as a plaster base. Plasterers may need to remove the existing wood lath to maintain the woodwork’s reveal. Rock lath is a 16×36-inch, 1/2-inch thick, gypsum-core panel covered with absorbent paper with gypsum crystals in the paper. The crystals in the paper bond the wet plaster and anchor it securely. This type of lath requires two coats of new plaster–the brown coat and the finish coat. The gypsum lath itself takes the place of the first, or scratch, coat of plaster.

Painting New Plaster

The key to a successful paint job is proper drying of the plaster. Historically, lime plasters were allowed to cure for at least a year before the walls were painted or papered. With modern ventilation, plaster cures in a shorter time; however, fresh gypsum plaster with a lime finish coat should still be perfectly dry before paint is applied–or the paint may peel. (Plasterers traditionally used the “match test” on new plaster. If a match would light by striking it on the new plaster surface, the plaster was considered dry.) Today it is best to allow new plaster to cure two to three weeks. A good alkaline-resistant primer, specifically formulated for new plaster, should then be used. A compatible latex or oil-based paint can be used for the final coat.

A Modern Replacement System

Veneer Plaster. Using one of the traditional lath and plaster systems provides the highest quality plaster job. However, in some cases, budget and time considerations may lead the owner to consider a less expensive replacement alternative. Designed to reduce the cost of materials, a more recent lath and plaster system is less expensive than a two-or-three coat plaster job, but only slightly more expensive than drywall. This plaster system is called veneer plaster.

The system uses gypsum-core panels that are the same size as drywall (4×8 feet), and specially made for veneer plaster. They can be installed over furring channels to masonry walls or over old wood lath walls and ceilings. Known most commonly as “blue board,” the panels are covered with a special paper compatible with veneer plaster. Joints between the 4-foot wide sheets are taped with fiberglass mesh, which is bedded in the veneer plaster. After the tape is bedded, a thin, 1/16-inch coat of high-strength veneer plaster is applied to the entire wall surface. A second veneer layer can be used as the “finish” coat, or the veneer plaster can be covered with a gauged lime finish-coat–the same coat that covers ordinary plaster.

Although extremely thin, a two-coat veneer plaster system has a 1,500 psi rating and is thus able to withstand structural movements in a building or surface abrasion. With either a veneer finish or a gauged lime putty finish coat, the room will be ready for painting almost immediately. When complete, the troweled or textured wall surface looks more like traditional plaster than drywall.

The thin profile of the veneer system has an added benefit, especially for owners of uninsulated masonry buildings. Insulation can be installed between the pieces of furring channel used to attach blue board to masonry walls. This can be done without having to fur out the window and door jambs. The insulation plus the veneer system will result in the same thickness as the original plaster. Occupants in the rooms will be more comfortable because they will not be losing heat to cold wall surfaces.

Patching Materials

Plasterers generally use ready-mix base-coat plaster for patching, especially where large holes need to be filled. The ready-mix plaster contains gypsum and aggregate in proper proportions. The plasterer only needs to add water.

Another mix plasterers use to patch cracks or small holes, or for finish-coat repair, is a “high gauge” lime putty (50 percent lime; 50 percent gauging plaster). This material will produce a white, smooth patch. It is especially suitable for surface repairs.

Although property owners cannot duplicate the years of accumulated knowledge and craft skills of a professional plasterer, there are materials that can be used for do-it-yourself repairs. For example, fine cracks can be filled with an all-purpose drywall joint compound. For bridging larger cracks using fiberglass tape, a homeowner can use a “quicksetting” joint compound. This compound has a fast drying time–60, 90, or 120 minutes. Quick-setting joint compound dries because of a chemical reaction, not because of water evaporation. It shrinks less than all-purpose joint compound and has much the same workability as ready-mix base-coat plaster. However, because quick-set joint compounds are hard to sand, they should only be used to bed tape or to fill large holes. All-purpose point compound should be used as the final coat prior to sanding.

Homeowners may also want to try using a ready-mix perlited base-coat plaster for scratch and brown coat repair. The plaster can be hand-mixed in small quantities, but bagged ready-mix should be protected from ambient moisture. A “millmixed pre-gauged” lime finish coat plaster can also be used by homeowners. A base coat utilizing perlite or other lightweight aggregates should only be used for making small repairs (less than 4 ft. patches). For large-scale repairs and entire room replastering, see the precautions in Table 1 for using perlite.

Homeowners may see a material sold as “patching plaster” or “plaster of Paris” in hardware stores. This dry powder cannot be used by itself for plaster repairs. It must be combined with lime to create a successful patching mixture.

When using a lime finish coat for any repair, wait longer to paint, or use an alkaline-resistant primer.

Summary

The National Park Service recommends retaining historic plaster if at all possible. Plaster is a significant part of the “fabric” of the building. Much of the building’s history is documented in the layers of paint and paper found covering old plaster. For buildings with decorative painting, conservation of historic flat plaster is even more important. Consultation with the National Park Service, with State Historic Preservation Officers, local preservation organizations, historic preservation consultants, or with the Association for Preservation Technology is recommended. Where plaster cannot be repaired or conserved using one of the approaches outlined in this Brief, documentation of the layers of wallpaper and paint should be undertaken before removing the historic plaster. This information may be needed to complete a restoration plan.

Plaster Terms

Scratch coat. The first base coat put on wood or metal lath. The wet plaster is “scratched” with a scarifier or comb to provide a rough surface so the next layer of base coat will stick to it.  

Brown coat. The brown coat is the second application of wet, base-coat plaster with wood lath or metal systems. With gypsum board lath (rock lath, plasterboard), it is the only base coat needed.  

Finish coat. Pure lime, mixed with about 35 percent gauging plaster to help it harden, is used for the very thin surface finish of the plaster wall. Fine sand can be added for a sanded finish coat.

Casing Bead. Early casing bead was made of wood. In the 19th century, metal casing beads were sometimes used around fireplace projections, and door and window openings. Like a wood ground, they indicate the proper thickness for the plaster.

Corner Bead. Wire mesh with a rigid metal spline used on

Outside corners. Installing the corner bead plumb is important.  

Cornerite. Wire mesh used on inside corners of adjoining walls and ceilings. It keeps corners from cracking.  

Ground. Plasterers use metal or wood strips around the edges of doors and windows and at the bottom of walls. These grounds help keep the plaster the same thickness and provide a stopping edge for the plaster. Early plaster work, however, did not use grounds. On early buildings, the woodwork was installed and primed before plastering began. Some time in the early 19th century, a transition occurred, and plasterers applied their wall finish before woodwork was installed.  

Gypsum. Once mined from large gypsum quarries near Paris (thus the name plaster of Paris), gypsum in its natural form is calcium sulfate. When calcined (or heated), one-and-a-half water molecules are driven off, leaving a hemi-hydrate of calcium sulfate. When mixed with water, it becomes calcium sulfate again. While gypsum was used in base-coat plaster from the 1890s on, it has always been used in finish coat and decorative plaster. For finish coats, gauging plaster was added to lime putty; it causes the lime to harden. Gypsum is also the ingredient in moulding plaster, a finer plaster used to create decorative moldings in ornamental plaster work.

Lime. Found in limestone formations or shell mounds, naturally occurring lime is calcium carbonate. When heated, it becomes calcium oxide. After water has been added, it becomes calcium hydroxide. This calcium hydroxide reacts with carbon dioxide in the air to recreate the original calcium carbonate.

Screed. Screeds are strips of plaster run vertically or horizontally on walls or ceilings. They are used to plumb and straighten uneven walls and level ceilings. Metal screeds are used to separate different types of plaster finishes or to separate lime and cement plasters.

What does not exist, however, is a ready-supply of competent, capable contractors to repair and restore slate roofs.  With a basic understanding of this highly-specialized roofing system, home owners can generally assess the current condition of their slate roof, its life expectancy and, if necessary, the potential for restoration.  The information that follows will help in assessing and identifying your roof’s needs as you, armed with this information, carefully screen potential roofing contractors to effect these repairs.  Olde Mohawk Masonry & Historic Restoration is the preferred contractor for such work in New York and New England.

What goes wrong with slate roofs?

In most instances, the problem is one of the following:

• Variations in duration and quality

• Flashings and other metalwork need replacement

• Earlier repairs by irresponsible roofing contractors 

Variations in duration and quality of slate

Slate is pulled from the earth in massive slabs and dressed down into individual shingles mostly by hand.  Slate is stone, and stone is long lasting. However, stone is a natural material and may have minute or even invisible fissures that will ultimately cause slates to break and slide off the roof.  Roofing slates are rated by ANSI according to hardness.  Softer slates (rated S2 or S3) may become crumbly and will delaminate, sometimes, as early as 55 years, and certainly by 80-100 years.  These softer slate roofs (commonly from Pennsylvania) cannot be saved or restored, for the most part, but repairs can buy time.  

Good, hard slates, like most New York, Vermont, Peach Bottom, Buckingham, or Monson slates, will last for hundreds of years on a properly cared for roof.  It is critical that people who own, inspect or work on slate roofs are able to identify the slate on the roof in question.  This single-most important information will provide details as to its type, origin, longevity, characteristics, and qualities.  Contact Olde Mohawk for a free consultation specific to your slate roof.  Roofing slate is still being quarried and sold in New York and Vermont (as well as Pennsylvania and Virginia.)   Slate was also once quarried in Georgia and Maine (home of the world-famous Monson slate.)

Flashing replacement and built-in gutters

While the slate may last “forever,” the metal flashings will not.  Flashings are essentially the metalwork used to prevent the penetration of water wherever there is an abrupt angle or opening in the roof (ie, chimneys, valleys, dormers.)  Often, flashings were made from terne-coated steel, which is a steel coated with a lead/tin combination.  This is sometimes, incorrectly, called “tin.”  Terne-coated steel has to be painted regularly or corrosion will occur.  

Copper flashings (either plain copper or lead-coated) were most commonly installed  on government buildings, churches, and similar institutions and upscale homes.  Copper will oxidize as vert de gris appears.  Copper will begin to fail after about 60 to 70 years in areas of high wear, such as valleys.  The copper industry suggests a life of 80 years.  Older copper flashings can be painted in order to extend their lives.  Too often, the flashings fail and unscrupulous roofing contractors convince homeowners to replace their good, slate roof with asphalt.  Only the flashings should be replaced, not the entire roof.

These types of projects are routine for slate roof restoration contractors.  The adjoining slates are removed to allow for replacement of the flashings.  The removed slate are then installed in their original locations, laving the roof, in appearance, as it was before, except for the flashing.  The standard upon which a repair is judged is that it must not appear to the layperson that any repair, at all, took place, except for new, visible flashings.

Box gutter linings, or “built-in” gutters, are another common problem on old slate roofs because the metal deteriorates and leaks. Just like valleys and other flashings, they can be replaced without removing and replacing the entire roof.  If left unchecked, the entire gutter boxes will rot and need to be rebuilt and replaced.

Beware of irresponsible roofing contractors

The cause of many leaking slate roofs is not natural wear, metal failures, or even cracked slates.  It is, quite simply, bad work.  Many unqualified people claim to have the ability to repair slate roofs.  Fully half of the work done annually by a typical slate roofing contractor involves the removal and replacement of faulty repair work.  Home owners with slate roofs often pay exorbitant sums to have their roofs trashed by these fly-by-nighters, then they have to pay even more of their hard-earned money to have them fixed and repaired correctly.  The types abuses committed against slate roofs include the ones that are face-nailed, tarred, repaired with non-matching slates, coated, or reflashed incorrectly (see photos below).  One should NEVER tar or coat the surfaces of slate roofs.  Such actions are aesthetically displeasing, often irreversible, and ineffective.  Roofing contractors are notorious for advising homeowners to replace a perfectly good roof.  Home owners will often listen to such advice when a lack of competent slaters makes it the only advice available.  These issues, combined, have been the downfall of countless slate roofs, lost forever to ignorance, neglect, and despair. Contact Olde Mohawk for a free assessment and discussion of your roof’s needs.  As you seek estimates and advice from other roofers, use the information in this document to test their knowledge and screen their methods.  Watch their eyes widen as they realize YOU know more about slate roofing than they do! 

Replacing broken and missing slate

It is not uncommon for a century-old slate roof to have 50 or more slates simply fail from a variety of causes.  Slate contains natural faults or hairline cracks and may eventually break.  A 20 square roof (2,000 square feet), with a typical 10″x 20″ slate, will have about 3,400 slates.  If 50 of them fail after a hundred years, then the failure rate of the roof is 1.5 percent over 100 years— or a 98.5 percent success rate over a century.   That’s an A+.   However, just one missing slate is all a leak needs to get started.  For a professional slater, the solution is not rocket science.  Replacement slates must never be fastened in place with visible straps or exposed nails (known as “face-nails”).  I repeat, if a roofer describes face-nailing to you as his preferred method, tell him to leave your property IMMEDIATELY. NEVER let him on your roof and ask him to forget your address.  Ask that he not even look at the slate if he ever happens to drive past your house in the future!

There are two acceptable techniques for fastening replacement slates:  the “nail and bib” method or the “slate hook”.  The nail and bib method is the most widely used. The broken slate is removed with a slate ripper and the replacement slate is anchored with a nail in the slot between the two, overlying slates.  A small square of flashing is slid under the two, overlying slates on the next course, above, and over the new nail head.  The bib is bent a little so friction keeps it in place.  Bibs can be aluminum, copper, or other non-corrodible metal, but shiny and reflective metals that are visible from the ground should never be used. 

Copper or brown-painted aluminum (coilstock) blends nicely into the roof.  A slate hook is a hard wire hook made of galvanized steel, copper or stainless steel, approximately three inches long.  A small exposed loop hooks the replacement slate in place. This is one instance when an exposed repair device is acceptable because the tiny hook is almost invisible from the ground.  Stainless steel hooks are stronger than copper hooks.  Slate hooks are preferable to the nail and bib on new slate roofs, especially for repairs in the field of the roof.  Using straphangers to repair the roof should be avoided; they’re unsightly and they deface the roof.

The tool required for removing slates from a roof is the slate ripper—a swordlike object that slides up under the slate and yanks out the two nails that hold it in place.  You never want to cut the nail because the piece of nail left under the slate will interfere with sliding the replacement slate into place.  A slate hammer, another important slate roofing tool, has a hole punch at one end used to punch nail holes in slates.  New slates can be hard and brittle and require some practice for easy punching with a slate hammer.  Standard thickness slates (3/16″ to 1/4″) are readily cut with a simple hand-held device, a slate cutter.

Conclusion

While the slate roof may last “forever,” the metal flashings will not.  Not all slate is the same in quality and durability. Unscrupulous roofers will butcher your roof or even replace it with asphalt shingles, if you let them.  Armed with the above information, you are ready to question potential slaters and assess your roof’s needs.  Please contact Olde Mohawk so that we may assist you.

Additional reading

Historic homeowners, the steward of historic buildings, and others can learn more about the Secretary of the Interior’s standards for restoring and preserving slate roofs.  Click on the link, below, to visit the National Park Services website.  There you’ll find a Technical Preservation Series brief on this and other topics. 

Preservation Brief #29:  The Repair, Replacement & Maintenance of Historic Slate Roofs

Real, thin stone veneer and manufactured stone veneer haven’t changed all the rules-they’ve shattered them. Across the nation, from banks to restaurants to retail stores and high end homes, stone veneer has turned the stone masonry world on its ear. In new construction applications, the savings and advantages are simple:  veneer doesn’t need a concrete footing that starts below the frost line, like conventional masonry. And installation occurs at a rapid rate, slashing labor costs.

But there’s an even more attractive application: Retrofit.  Now, buildings and homes with dated brick, EFIS and vinyl siding can get a facelift for the million-dollar-look of the end product for a fraction of the price!  Real stone veneer can change the look of a ‘Brady Bunch’-style home from the 1970′s and its outdated fireplace inside. Too often, in new construction homes, the foundations are ugly, poured concrete. Stone veneer allows customers to put the “finishing touch” on a high-end project. 

Perhaps the most important contribution stone veneer can make is in its commercial applications. New buildings can have the look and appeal of stone for far less than previously thought. Existing businesses can take advantage of a whole new look, virtually a new building, for short money when compared to the cost of new, commercial construction. Contact Olde Mohawk today to learn how stone veneer can improve your home or business!

The most prevalent argument against slate is the cost. Realistically, a homeowner can expect to pay $3.50/sq’ for a new asphalt shingle roof, compared to $12 to $14/sq’ for slate. Consider the average, 20 square roof: asphalt shingles, $7,000; slate, $26,000. After the third asphalt roof, the slate has paid for itself, never mind the added cost factors for inflation. “But”, you say, “I’m not going to live in my house for 60 years. I will never personally appreciate these savings.”

Not so fast. The average consumer who lives in a home for 30 years will replace the roof twice. And, when it’s time to sell, your home has the added, positive feature of a slate roof. Any realtor will tell you: This adds tremendous charm, curb appeal, value, and it boosts the price tag when you go on the market. Slate roofing is good for your wallet, and our planet!

First and foremost, a warning straight from the heart: One should NEVER tar or coat the surface of a slate roof. Such actions are aesthetically displeasing, often irreversible, and ultimately ineffective. Sadly, roofing contractors are notorious for advising homeowners to replace a perfectly good roof. Home owners will often listen to such advice when a lack of competent slate roofers makes it the only advice available. These issues, combined, have been the downfall of countless slate roofs, lost forever to ignorance, neglect, and despair. As you seek estimates and advice from other roofers, use the information in this blog to test their knowledge and screen their methods. Watch their eyes widen as they realize that YOU know more about slate roofing than they do! 

It is not uncommon for a century-old slate roof to have 50 or more slates simply fail from a variety of causes. Slate contains natural faults or hairline cracks and may eventually break. A 20 square roof (2,000 square feet), with a typical 10″x 20″ slate, will have about 3,400 slates. If 50 of them fail after a hundred years, then the failure rate of the roof is 1.5 percent over 100 years- or a 98.5 percent success rate over a century. That’s an A+!   However, just one missing slate is all a leak needs to get started.  For a professional slate roofer, the solution is not rocket science. Replacement slates must never be fastened in place with visible straps or exposed nails (known as “face-nails”). If a roofer describes face-nailing to you as his preferred method of repair, you’re done-you’ve just met one of the butchers who roams about, masquerading as a slate roofer. NEVER let him anywhere near your roof!

There are two acceptable techniques for fastening replacement slates:  the “nail and bib” method or the “slate hook”. The nail and bib method is the most widely used. The broken slate is removed with a slate ripper and the replacement slate is anchored with a nail in the slot between the two, overlying slates. A small square of flashing is slid under the two, overlying slates on the next course, above, and over the new nail head. The bib is bent a little so friction keeps it in place. Bibs can be aluminum, copper, or other non-corrodible metal, but shiny and reflective metals that are visible from the ground should never be used. 

Oh and, by the way, all true slate roofers call themselves slaters. If a prospective roofing contractor doesn’t smile and embrace the term in your initial contact when you ask, “Are you a slater?” watch out! Just might be a butcher in disguise…

First, a little Mortar 101 is in order.   Mortar is typically made up of three dry components: a binder, an aggregate, and lime.  This is usually Portland cement, sand and hydrated lime.  It’s the ratio that determines the strength, or ASTM classification, of the mortar.  The pre-mixed bags found at home centers are usually ASTM type “S” mortars, similar to that used on commercial construction sites to lay modern brick and block walls.  It has lots and lots of Portland cement in it and probably differs wildly from the mortar found in the average historic home.  Before 1872 in the United States, there was no such thing as Portland cement.  Mortar was generally lime and sand mixed, or lime, sand and natural cement (discovered in the 1820′s during construction of the Erie Canal in upstate New York.)

The paradox of a masonry structure is that it’s strength comes from it’s ability to fail.  Well, what the heck does that mean you’re wondering.  And rightly so.  Here’s how an old friend best explained it to a class of preservation students:  Masonry units, be it brick, stone or block, are laid in mortar.  That mortar absorbs and expels moisture.  Moisture is water, and water freezes.  When it freezes it expands, increasing volume by as much as 12% in the case of an ice cube.  So, in a sense, the mortar expands, even minutely.  Something has to give:  the brick or the mortar.  If the mortar is ‘harder’ (meaning a high cement content) than the bricks laid in it, the bricks will spall and pop, their faces crumbling and falling off.  But if the bricks are ‘harder’ the mortar will give, often without cracking or falling apart or leaving any visible record of the strength through failure.  And, if the mortar joints do fail, it’s FAR less expensive to repoint masonry than it is to rebuild it!

A good mason will be able to mix up a repointing mortar that will not jeopardize the historic masonry fabric of your home or building.  If the color or texture are more challenging, there are firms available on-line that will custom match mortar samples for under $200.  That’s right folks, you can cry Foul! the next time a mason says “I can repoint your brick wall but I can’t match the old joints where they meet,” “It’ll take a couple years for it to blend in, if ever,” or, worse, “It’ll never match.” This is the same guy who buys bags of pre-mix mortar at Home Depot and repoints old, soft-brick chimneys. After a couple of winters, the chimney is crumbling and falling apart. If he’s really slick, they unwittingly call him back to ultimately rebuild the chimney that he destroyed!

A good repointing job should last at least thirty years. But, like most things in life, you get what you pay for.  The cheapest guy, or the one who says “I can’t match it,” will look like a deer in the headlights if you start using terms like compressive strength, Portland cement, or lime putty mortar.  If you start to think, “Maybe I know more about this than he does,” you probably do.  You should ask for three references-specifically-for recent repointing jobs and then go look at his work.  A good mason contractor will not spend his free time forever going back and forth with you providing endless references and answering questions ad nauseum.  He’s busy, in demand, and doesn’t desperately NEED your job.  But he’ll give you a comprehensive consultation and estimate and he’s got half a dozen references ready for a potential customer. 

There are many stories of repointing projects gone horribly wrong-don’t let it happen to you!

No contractor is a master of all skill sets in a given trade. Let’s look at masonry as an example. There are some masonry outfits that do nothing but stamped concrete.  Because it’s all they do, they’re set up for it:  the tools, equipment and crews who are proficient in their craft. This allows them to offer a quality product at a competitive price. Now consider the mason whose company primarily builds block and brick walls for commercial customers on a regular basis. He may be able to successfully complete a stamped concrete project, but there’s a lot more planning and set-up involved, and he may have less-skilled workers for that particular project. Hence, his price is likely to be higher and there’ll be less examples of his work for you to consider. The contractor you hire must have the tools, equipment, craftsmen, and experience needed to successfully complete your project.

Consider this analogy as it applies to restoration work. The knowledge and skill sets required to successfully rebuild a copper-lined, Philadelphia-style gutter on an old Colonial with a slate roof bring three trades into action:  metal work, carpentry, and slate roofing. There are many carpenters who would find the copper-smithing and slate aspects of the job beyond their abilities. And many slaters are not capable of replicating the ornate cornice, corbels and detail of a built-in gutter. It is critical that a contractor provide you with more than a fancy proposal and attractive price for your project. He needs to demonstrate and prove himself through pictures, documentation and references for similar projects that he has already successfully completed.

Being a successful restoration contractor requires knowledge of the tools, materials and practices of tradesmen from yesteryear. One cannot rely on the best practices of modern construction, alone, as a basis of knowledge. Constant research through hundred-year-old trade manuals, the internet, and hands-on experience are the foundation on which a preservation worker basis his decisions and guides his crew through a project. It is a constant learning process and one that requires a high degree of interest and commitment to professional development. Make sure your prospective contractor is genuinely interested in the work on your home or building.

While we’re on topic some words of caution are in order. Make certain that he’s licensed and insured, as your city and/or state may require. Some states, like Massachusetts and Rhode Island, require a construction supervisor’s licensing or registration with the state contractors’ board. This type of  information  is easily accessed through the internet. Make certain to call your town or city building department to confirm what you find. If a permit is required, the contractor MUST secure it. If you fall for the old, “You pull the permit and I’ll give you a price break,” watch out. If any person is injured or property damaged during the job, it’ll fall on your shoulders-you were the sneaky little devil who pulled the permit to save a few bucks. Most contractors who try this scam DO NOT have the insurances your town or city requires to grant the permit!  You are making a significant investment in your home or building; don’t cut corners when it comes to a permit.

It never ceases to amaze me how few clients ask for proof of the right insurance. Your contractor MUST have liability AND workers compensation insurances. General liability insurance for a MINIMUM $1 million personal injury and a MINIMUM $1 million property damage ARE NOT cost prohibitive for a restoration worker proposing to do high end work. A common scam many contractors run is to act like they have liability insurance, and that’s good enough. Of equal or possibly greater importance is workers’ comp. This one costs the big bucks and is what drives a legitimate contractor’s prices up. However, it is also his protection AND YOURS if an employee gets hurt on the job. If an employee gets injured on your property and files a comp claim where coverage was NOT in effect, he can sue his employer AND YOU!  Verify that your restoration contractor has workers’ compensation insurance and provides you with a general liability certificate naming you and the property as ‘additionally insured parties.’

Following these simple guidelines will help you find the right outfit for your restoration project and get things moving in the right direction!

Surfing the web on a cold, Saturday evening in December, I find myself amazed at how few articles or blogs cut through the fluff and filler of hiring a contractor to address a topic critical to the success of your next project:  finding the right guy for the job!  An item I don’t see addressed at all is the importance of finding the right contractor for the project at hand. While it seems like an obvious statement to make, and a simple enough obstacle to overcome, it is the single-most important element to the success of the project and ultimate satisfaction of you, the consumer.

No contractor is a master of all skill sets in a given trade. Let’s look at masonry as an example. There are some masonry outfits that do nothing but stamped concrete.  Because it’s all they do, they’re set up for it:  the tools, equipment and crews who are proficient in their craft. This allows them to offer a quality product at a competitive price. Now consider the mason whose company primarily builds block and brick walls for commercial customers on a regular basis. He may be able to successfully complete a stamped concrete project, but there’s a lot more planning and set-up involved, and he may have less-skilled workers for that particular project. Hence, his price is likely to be higher and there’ll be less examples of his work for you to consider. The contractor you hire must have the tools, equipment, craftsmen, and experience needed to successfully complete your project.

Consider this analogy as it applies to restoration work. The knowledge and skill sets required to successfully rebuild a copper-lined, Philadelphia-style gutter on an old Colonial with a slate roof bring three trades into action:  metal work, carpentry, and slate roofing. There are many carpenters who would find the copper-smithing and slate aspects of the job beyond their abilities. And many slaters are not capable of replicating the ornate cornice, corbels and detail of a built-in gutter. It is critical that a contractor provide you with more than a fancy proposal and attractive price for your project. He needs to demonstrate and prove himself through pictures, documentation and references for similar projects that he has already successfully completed.

Being a successful restoration contractor requires knowledge of the tools, materials and practices of tradesmen from yesteryear. One cannot rely on the best practices of modern construction, alone, as a basis of knowledge. Constant research through hundred-year-old trade manuals, the internet, and hands-on experience are the foundation on which a preservation worker basis his decisions and guides his crew through a project. It is a constant learning process and one that requires a high degree of interest and commitment to professional development. Make sure your prospective contractor is genuinely interested in the work on your home or building.

While we’re on topic some words of caution are in order. Make certain that he’s licensed and insured, as your city and/or state may require. Some states, like Massachusetts and Rhode Island, require a construction supervisor’s licensing or registration with the state contractors’ board. This type of  information  is easily accessed through the internet. Make certain to call your town or city building department to confirm what you find. If a permit is required, the contractor MUST secure it. If you fall for the old, “You pull the permit and I’ll give you a price break,” watch out. If any person is injured or property damaged during the job, it’ll fall on your shoulders-you were the sneaky little devil who pulled the permit to save a few bucks. Most contractors who try this scam DO NOT have the insurances your town or city requires to grant the permit!  You are making a significant investment in your home or building; don’t cut corners when it comes to a permit.

It never ceases to amaze me how few clients ask for proof of the right insurance. Your contractor MUST have liability AND workers compensation insurances. General liability insurance for a MINIMUM $1 million personal injury and a MINIMUM $1 million property damage ARE NOT cost prohibitive for a restoration worker proposing to do high end work. A common scam many contractors run is to act like they have liability insurance, and that’s good enough. Of equal or possibly greater importance is workers’ comp. This one costs the big bucks and is what drives a legitimate contractor’s prices up. However, it is also his protection AND YOURS if an employee gets hurt on the job. If an employee gets injured on your property and files a comp claim where coverage was NOT in effect, he can sue his employer AND YOU!  Verify that your restoration contractor has workers’ compensation insurance and provides you with a general liability certificate naming you and the property as ‘additionally insured parties.’

Following these simple guidelines will help you find the right outfit for your restoration project and get things moving in the right direction!