PRESERVATION 

BRIEFS 

Preserving Historic Ornamental Plaster 

David Flaharty 

U.S. Department of the Interior 

National Park Service 

Cultural Resources 

Heritage Preservation Services 

From the time America struggled for a new identity as 

a constitutional republic-and well into the 20th 

century-its architecture and its decorative detailing 

remained firmly rooted in the European classicism of 

Palladio, Wren, and Mansart. 

Together with skilled masons and carpenters, ornamental plasterers saw their inherited trade flourish 

from the mid-18th century until the Depression years of 

the 1930s. During this two hundred year period, as the 

Georgian and Federal styles yielded to the revivalsGreek, Rococo, Gothic, Renaissance, and Spanishdecorative plaster reflected each style, resulting in the 

wide variety of ornamentation that survives. The traditional methods of producing and installing interior 

decorative plaster were brought from Europe to this 

country intact and its practice remains virtually unchanged to this day. 

Fig. 1. Ornamental plaster studios employed the following personnel: Draftsmen to interpret architectural details in shop drawings; sculptors who 

modelled in clay; model makers who assembled sculpted, plain-run and pre-cast elements into an ornamental unit; moldmakers who made rigid or 

flexible negative tooling; casters who made production units; finishers (often the caster's wives) who cleaned the casts; and laborers who assisted 

skilled personnel in operating efficiently. This studio was in Philadelphia, c. 1915. Photo: Courtesy, M. Earle Felber. 
Styles of Decorative Plaster in America, 

18th-20th Centuries 

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(a) Kenmore, Fredericksburg, Virginia. c. 1752. Georgian in style with ornamental ceilings based on Batty Langley's 1739 English style book, the plasterwork was executed by a Frenchman in the mid-1770s. This house was built by 

Col. Fielding Lewis and has the most elaborate ornamentation of any in the 

period. Photo: Historic American Buildings Suroey Collection. 

(b) Old West Church, Boston, Massachusetts. c. 1806. Designed by Asher 

Benjamin, this church in the Federal-Adamesque style became the prototype 

for many other New England churches through publication of plans in Benjamin's American Builder's Companion. Photo: Courtesy, Stanley P. Mixon (copy). 

(c) Lyndhurst, Tarrytown, New York, c. 1838. This Gothic Revival villa on the 

Hudson River was built for financier Jay Gould by Alexander Jackson Davis. A 

versatile architect, Davis was simultaneously at work on Greek Revival buildings in New York City. Both styles called for elaborate ornamental plasterwork. 

Photo: Jack E. Boucher. Historic American Buildings Suroey. 

(d) Gaineswood, Demopolis, Alabama, c. 1842-60. These Greek Revival 

columns were drawn from Minard Lafever's The Beauties of Modern Architecture of 1835. This bold new style began in New York City and quickly spread 

south and west. Photo: Historic American Buildings Suroey Collection. 

(e) Ohio Theater, Columbus Ohio, c. 1928. An example of the "Golden Age" of 

movie palaces, Thomas Lamb's "Spanish" style interior is a typical example of 

the plasterwork executed just prior to the Depression years. Ornament was site 

cast, often on the stage, while the orchestra was scaffolded for installation. 

Photo: National Park Seroice files. 
Like flat walls and ceilings, historic ornamental plaster is 

made of gypsum and lime which are stable and durable materials. An extremely versatile material, plaster 

can be modelled, cast, incised, colored, stamped, or 

stencilled. However, as an integral part of the building 

system it is subject to the typical problems of water 

intrusion, structural movement, vibration and insensitive alterations, both incrementally and from adaptive 

use projects. This Preservation Brief has been prepared 

to assist property owners, architects, contractors, and 

Federal agency managers in identifying the causes of 

ornamental plaster failure, specifying repair and replacement techniques and engaging qualified professionals to do the work. The scope of this Brief is 

limited to the repair and restoration of existing ornamental plaster; certain forms of decorative plaster such 

as scagliola, composition ornament, and artificial Caen 

Stone are not addressed, nor is the design and installation of ornamental plasterwork in new construction. 

Finally, guidance on using substitute materials to 

match the historic appearance of ornamental plasterwork-a legitimate option within the Secretary of Interior's Standards for Historic Preservation Projects-is not 

discussed here, but will be the subject of another Brief 

on interiors. 

The Ornamental Plaster Trade 

Shop Personnel. As builders and architects were hired 

by an increasingly affluent clientele, ornamental plaster 

shops developed from the single artisan operations of 

the 18th century into the complex establishments of the 

early 20th century. American plaster studios employed 

immigrant and, later, native craftsmen (see Fig. 1). 

Plasterers' guilds were in existence in Philadelphia in 

the 1790s. In 1864, a plasterers' union was organized in 

the United States with members from the British Isles 

whose work there had been limited to palaces and 

churches. English and European craftsmen came to 

America where the demand for their skills had increased by the decade, offering them the unparalleled 

opportunity to open their own shops. Over the years, 

plaster elements became so popular in decorating interior spaces that a major industry was established. By 

the 1880s, catalogs were available from which property 

owners could select ornamentation for their splendid 

new buildings (see Fig. 2). 

Methods of Production. Historically, ornamental plasterwork has been produced in two ways: it would be 

run in place (or on a bench) at the site; or cast in molds in 

a workshop. Plain plaster molding without surface 

ornamentation was usually created directly on the wall, 

or run on a flat surface such as a plasterer's workbench 

and attached to the wall after it set. Ornament such as 

coffering for ceilings, centers for light fixtures (medallions), brackets, dentils, or columns were cast in hide 

glue (gelatin) or plaster molds in an offsite shop, often 

in more than one piece, then assembled and installed 

in the building. 

Decorative Plaster Forms-Cornices, Medallions, 

Coffers. Three decorative plaster forms in particularthe cornice, the ceiling medallion, and the coffered 

ceiling-historically comprised much of the ornamental 

Fig. 2. This parlor medallion and pendant drops shown in a mid19th century row house in Annapolis, Maryland were originally 

ordered from a catalog. A local plasterer ran the plain cornice and 

band ribbon, the curved corners of which were bench run, set with a 

plaster adhesive and pointed at the joints. Photo: M. E. Warren . 

plasterers' business. These forms appear individually 

or in combination from the 18th to 20th century, irrespective of stylistic changes. 

For example, an elaborate parlor cornice consisted of 

plain moldings made of gypsum and lime run atop 

temporary lattice strips around the room. Tooling for 

plain-run moldings called for a sheet metal template of 

the molding profile mounted on a wooden "horse" (see 

Figs. 3 and 4). Mitering was accomplished using a plaster and lime putty gauge (mix) tooled with miter rods 

at the joints (see Fig. 5). Decorative "enrichments" 

such as leaves, egg and dart moldings, and bead and 

reel units were cast in the shop and applied to the 

plain runs using plaster as an adhesive (see Fig. 6). 

Painting, glazing, and even gilding followed. Large 

houses often had plain- run cornices on the upper floors 

which were not used for entertaining; modest houses also 

boasted cornice work without cast enrichment. 

Among the most dramatic of ornamental plaster forms 

is the parlor ceiling medallion. Vernacular houses often used plain-run concentric circles from which lighting fixtures descended, usually hung from a wrought 

iron hook embedded in the central ceiling joist. More 

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Tools of the Trade 

Running Molds 

Fig. 3. A running mold consists of a sheet metal profile blade nailed 

to a stock and slipper. A triangular brace also acts as a handle. Such 

a mold produces a clean plain plaster molding if it travels in the 

same place each pass as a gypsum and lime putty gauge is troweled 

ahead of the moving blade. (A) is a typical mold for a cornice; (B) 

produces a diminished run as the hinges close together; and (C) is a 

pin mold that is used to surround elliptical forms such as arches. In 

addition, running molds may revolve around pivot points, trammels, and mandrels. 

Fig. 4. Running a Cornice. The historic method of producing a 

cornice is unchanged today. A running mold or template is pushed 

along a lattice strip nailed to the wall. Base coat plaster is gypsum 

and sand; finishing plaster is added with small tools and stuffed 

wearing rubber gloves because lime burns the skin. As many as 20 

passes are required to complete a smooth run; this particular cornice 

was formed in two stages, top and bottom, because it was so large. 

Cornices this size also have to be blocked and lathed to minimize the 

amount of applied material. Photo: Old-House Journal. 

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Fig. 5. Mitering a Plain-Run Cornice. Mitering requires great 

dexterity using the miter rod. In this case, a return at a chimney 

breast is tooled using an infill of gypsum and lime. Internal and 

external miters are required with the internal being the most difficult. Another method is to run a length of cornice (using the same 

blade) on a bench and set it in place, later to point the joints. Photo: 

Old-House Journal. 

Fig. 6. Enriching a Plain-Run Cornice. After a cornice is run and 

mitered, cast enrichments are stuck in recessed sinkages planned to 

receive the casts. Ornamental models are made to engage with one 

another, resulting in unbroken lines or courses. A shop-cast ornament is soaked in water until saturated and pressed into its sinkage 

using wet plaster as an adhesive. Once the casts have been installed, 

they are carefully pointed at the joints and at the miters so that they 

appear as a continuous, repetitive design. Photo: Old-House Journal. 

elaborate medallions were composed of shop-cast 

pieces, such as acanthus foliage often alternating with 

anthemia or other decorative designs. Medallions usually related stylistically to the cornice ornament found 

in the room and could be created with or without a 

plain-run surround (see Fig. 7). Of particular importance to the art of ornamental plaster was the mid-19th 

century double parlor plan. Architects often specified 

matching medallions of robust proportions and ornamentation. Later, in 20th century American Colonial 

Revival architecture, architects called for Federal style 

ceiling medallions. Some of the more successful were 

graceful one-piece units, utilizing classical motifs such 

as garlands and swags, and in their simplicity, reminiscent of Adamesque designs of the 1760s. 
Fig. 7. Running and Enriching a Ceiling Medallion . The method of 

running and enriching a ceiling medallion remains the same today. 

(a) First, a plain-run surround is spun from a pivot point centered 

in the ceiling field. (b) Ornament layout is determined using plane 

geometric principles; segmented locations are deeply scratched to 

provide a rough surface for adequate bonding using plaster as an 

adhesive. Historically, cast enrichments could be bought from local 

suppliers and set individually, allowing architects to compose 

medallions to suit room dimensions and period motifs. 

Photos: Peter Sanders. 

Yet another significant decorative form is the coffered 

ceiling. Coffering units were cast in the shop or onsite, 

then installed with hanging wires to form the ceiling 

(see Fig 8). Ceiling design varied from period to period 

as to depth, panel shape, and ornamental complexity. 

Not always flat, coffering is seen inside domes, within 

barrel vaults and groin ceilings, along overhead ribs 

and soffits. Rosettes are usually centered in the panels 

and often enrich the intersections of elaborate stiles 

bordering the panels. Flat ceiling coffers are generally 

Fig. 8. Casting a Coffering Unit. Ceiling coffers are made the same 

way today except, historically, a hide glue mold was poured over an 

ornamental model whereas today urethane molding rubber is used. 

Now, as then, the plaster casts are made with steel channel irons 

embedded on the back of each panel. The coffers are hung from 

carrying irons fixed to the ceiling above by means of twisting wires to 

level each coffer to its neighbor. Aftenvard, the panels are fastened 

together and the joints pointed with plaster. Photo: David Flaharty. 

Fig. 9. The elaborate coffered ceiling was designed for the Willard 

Hotel in Washington, D.C. (1902-04) by Henry Janeway Hardenbergh. The coffered ceiling was restored as part of a rehabilitation 

project in the 1980s. Photo: Carol M. Highsmith. 

identical in reflected plan; on domed or barrel ceilings, 

coffers differ from course to course so as to appear 

identical from various sight lines. The finish treatment 

of a coffered ceiling frequently exhibits the height of 

the painter's craft. Foremost examples of ceiling coffering include the United States Capitol, and Washington 

D. c.'s Union Station. As a popular decorative form 

with inherent acoustical benefits, the coffered ceiling is 

seen across the United States in many large public 

spaces such as theaters, courthouses, railroad stations, 

and hotels (see Fig. 9). 

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Unfortunately, these supposedly enduring decorative 

forms created by ornamental plaster tradesmen are 

subjected to the ravages of both nature and man and, 

consequently, seldom remain as originally designed. 

Minor changes of taste are perhaps the least injurious 

to plasterwork. Considerably greater damage and deterioration are caused by radical changes in building use 

and poor maintenance practices. Fortunately, in most 

cases, the form, detailing, and finish of historic ornamental plaster can be recaptured through careful repair 

and restoration. 

Causes of Ornamental Plaster Damage 

Ornamental Plaster Substrate. For flat plaster walls and 

ceilings, as well as decorative forms, the system to attach interior plaster to walls and ceilings primarily consisted of 1/4" x 1-1/4" wooden lathing strips nailed 3/8" 

apart against studs and joists. First a scratch coat consisting of sand, lime, and cattle hair was troweled on 

the lath and pressed through the slots so as to slump 

over and form "keys." Next, a brown coat was applied 

to establish flat and plumb surfaces. The earliest plasterwork consisted of two coats of lime and sand plaster; later in the 19th century, a third or finish coat was 

applied that consisted of both lime and gypsum. Decorative units were generally attached to the substrate using 

plaster as an adhesive. 

Signs of Failure. Failure of the substrate is more typical 

than failure of the plaster ornament itself. Among the 

reasons for deterioration, structural movement (see Fig. 

10) and water intrusion (see Fig. 11) are the most deleterious. Buildings move and settle, causing deflection 

and delamination which result in stress cracking. These 

cracks often begin at the corners of windows and doors 

and extend upward at acute angles (see Fig. 12). Roof 

or plumbing leaks make finishes discolor and peel and 

cause efflorescence, especially on plain-run or enriched 

cornices. Unheated buildings with water intrusion are 

subject to freeze-thaw cycles which ultimately result in 

base coat and ornamental plaster failure (see Fig. 13). 

Fig. 10. Structural settling has caused this ceiling to deflect. Prior 

to restoring the damaged plaster and final repainting, a structural 

engineer experienced in historic preservation will be engaged to 

shore-up the ceiling from below and reattach the sagging ceiling 

plaster with the joists above (see also Fig. 17 under Immediate 

Action.) Photo: National Park Service files. 

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Fig. 11. The cornice of an Iowa courthouse has been severely damaged from a roof leak. In order to repair the ornamental plaster, a 

thixotropic rubber impression will be taken (with the paint build-up 

undisturbed). The efflorescence will be removed and fresh plaster 

casts installed so that egg and dart, dentil and leaf molding are 

perfectly aligned. Photo: National Park Service files. 

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Fig. 12. Settlement caused stress cracking through both flat wall 

and ornamental plaster. Repairs to the cornice molding involve 

chamfering the stress cracks to a "V groove" and patching with a 

mixture of gypsum and lime. The cornice can be countersunkscrewed to its substrate to prevent further movement. Screw heads 

are then plastered over. The crack running through the painting will 

need to be filled carefully, and the painting restored by a trained 

conservator. Photo: Jack E. Boucher, Historic American Buildings 

Survey. 
Fig. 13. Water intrusion and freeze/thaw cycles caused extensive 

efflorescence and ornamental plaster failure . The plaster needed 

almost total replacement within the rehabilitation project. Photo: 

Commercial Photographics. 

Fig. 14. A mitered portion of this impost capital abacus has fallen, 

revealing the plaster adhesive material. Repairs are made by obtaining a section through the abacus, making a bench-run length, cutting, fitting, and readhering the missing piece. Finally, the joints 

are pointed. Photo: Lee H. Nelson, FAIA. 

In addition, keying and adhesive properties may be 

further jeopardized by weak original mixes (see Fig. 

14) that were improperly applied. Substrate failure typically results from faulty lathing or rusty lath nails, 

causing ceilings to fall. In the 20th century, vibration 

from heavy vehicular traffic, nearby blasting, and even 

repeated sonic booms may contribute to damaging 

ornamental plaster. Inadequate support in an original 

design may also be to blame when particularly heavy 

units have simply broken off over time (Fig. 15). Finally, new mechanical systems, suspended ceilings and 

partition walls insensitively installed in adaptive use 

projects, show little regard for the inspired decorations 

of earlier periods (see Fig. 16). 

Repairing and Replacing. Plaster failure is a matter of 

degree. For example, top coat failure can be repaired by 

Fig. 15. U. S. Treasury Cash Room, Washington, D.C. c. 1830. 

Designed by Robert Mills in the Greek Revival style, the unreinforced shell flutes most likely broke as a result of their weight. As 

part of an overall restoration of the room, the broken parts were 

molded on site, recast, then re-attached using wooden strips to pin 

them in place. Photo: Laurie R. Hammel. 

Fig. 16. The Auditorium Building, Chicago, Illinois, 1889, by Louis 

Sullivan. Earlier insensitive alterations were removed prior to restoration of the room. In the photo, a partition wall has already been 

removed; the electrical conduit and a ventilation grille followed. 

Plaster patching and painting were the final steps of restoration 

work. Photo: National Park Service files. 

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applying a new finish coat over a sound early substrate. Also, if cracking or loss of all three coats has 

occurred and is not combined with major structural 

failure, it can be repaired much like flat wall plaster. 

For ornamental plaster, however, repair beyond patching is often equivalent to targeted replacement of entire 

lengths or portions of run-in-place and cast ornamentation. Pieces that are deteriorated or damaged beyond 

plain patching must be removed and replaced with 

new pieces that exactly match the existing historic plaster. For this reason, partial restoration is often a more 

accurate term than repair. But whichever term is used, 

it is not recommended that repair of ornamental plaster 

be undertaken at any level by property owners; it is a 

craft requiring years of training and experience. A qualified professional should always be called in to make an 

inventory of ornamental plaster enrichments and to 

identify those details which are repairable onsite and 

which should be removed for repair or remanufacture 

in the shop. 

Immediate Action 

Once the cause and extent of damage have been determined, treatments such as shoring, stabilization, and 

limited demolition can begin, preparatory to repairing 

or restoring historic ornamental plaster. 

First, roof or plumbing leaks must be repaired to eliminate the problem of water intrusion. General structural 

repairs should be undertaken to arrest building movement, which weakens the base coat plasters to which 

the ornamental enrichments are attached. Ornamental 

plaster deflection should be corrected by shoring from 

below followed by re-anchoring (see Fig. 17). 

Testing for poor adhesion of base coat to lath or ornament to base coat, should be conducted to reduce further loss of enrichment. Adaptive use intrusions 

should be carefully removed to protect the existing 

decorative plasterwork. 

Code-required fire suppression systems should be evaluated at this time. Modern building codes may require 

heat/smokelflame detectors and automatic sprinkler 

systems of various types and applications. Fire suppression systems as well as all mechanical systems 

(HVAC, plumbing and electrical) systems should be 

designed so that they accomplish their purpose with 

minimal impact on the decorative plaster. Plumbing for 

an automatic sprinkler system, for example, can be run 

above new and existing coffering so that the sprinkler 

heads barely protrude from the rosette centers in the 

coffered design. Access should be provided for future 

system maintenance or repair. 

A 20th Century Shop Tour-Personnel, 

Materials, and Processes 

Before discussing how decorative forms such as cornices, medallions, and ceiling coffers are repaired onsite and in the shop by ornamental plasterers, the 

"shop tour" explains traditional casting processes used 

in conjunction with updated materials. A shop tour can 

be exciting, but confusing to the layman without some 

explanation of modeling, molding, and casting activities. For a prospective client, a visit to the plaster studio or site can be of value in choosing a qualified 

plastering contractor. 

Shop and Personnel. Generally, a highly functional 

shop should look well organized-that is, not in disarray with remnants of past projects lying about to impede current production. Old molds may be in 

abundance, but hanging from the wall or otherwise 

"on file." Machinery (saws and drill presses) and hand 

tools should appear well maintained. In short, one 

might evaluate such a studio as one does an auto mechanic's shop: does it inspire confidence? This is the 

time to look around and ask questions. What is the 

shop's past project work experience? Is the firm mostly 

in volved in new ccnstruction work or total reconstruction? More important than the way the shop looks, is 

the personnel sufficiently experienced in making repairs to historic decorative plaster? What about training 

and apprenticeships? How did the staff learn the 

trade? The more that is known about the total operation the better. 

Fig. 17 (a) Where this ceiling was suffering from structural failure, the first step was to shore it up from below. (b) Toggle bolts were used to reattach the plaster molding to the ceiling joists. The ceiling was then patched with gypsum and lime, prior to restoring the significant paint finishes. Photos: National Park Service files. 

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Molding Rubber. Familiarity with contemporary molding rubbers is desirable. There are several formulations 

currently on the market. In the past, flexible molds 

were made with hide glue melted in a double boiler 

and poured over plaster originals which had been prepared with an appropriate parting agent. Of the newer 

rubbers, latex (painted on the model coat by coat) is 

time consuming and has little dimensional accuracy; 

polysulfide distorts under pressure; and silicone is 

needlessly expensive. Urethane rubber, with a 30-

durometer hardness, is the current choice. Urethanes 

are manufactured as pourable liquids and as thixotropic pastes so that they can be used on vertical or overhead surfaces. The paste is especially useful for onsite 

impressions of existing ornament; the liquid is best 

used in the shop much as hide glue or gelatin was 

historically. Urethane rubber has the ability to reproduce detail as fine as a fingerprint and does not degrade during most ornamental plaster projects. No 

flexible molding material lasts forever, so spare casts 

should be maintained for future remolding. 

Molding Plaster. Molding plaster will also be in evidence; it is the product most similar to that used historically. This plaster is finely ground to accept the 

detail of the rubber molds, not so hard as to prohibit 

tooling, and combines readily with finish lime. Highstrength plaster is available in varying densities, some 

with added components for specific purposes. Most 

shops maintain these varieties, but use molding plaster 

for typical work. 

Sheet Metal Templates. The contractor's familiarity with 

sheet metal is critical. Accurate template blades are 

required to reproduce both straight and curved sections 

of moldings (see Fig. 3, above). The blades must be 

carefully cut, filed, and sanded in order to form exact 

reproductive units. A tour of a sizeable shop will include observation of running techniques and the 

results of this activity should be much in evidence. 

Regardless of size, these runs should be smooth and 

true when made by qualified craftsmen. 

Models. Models, whether of capitals, cornices, medallions or cartouches, are made as whole units or in parts 

depending on project demands. Completeness, accurate dimensions, and attention to historic styles are 

essential ingredients of successful models. Each part of 

a model has a name, i.e., dentil, guilloche, rinceau or 

bolection molding, modillion, egg and dart, and the 

designers and restorers of these ornaments should 

know their names. Failure to identify these parts correctly should be of concern to a prospective client. 

Molds. Molds are "negative forms" produced from 

completed models. Simple flood molds require a separator or barrier coat over the original and a surrounding fence to prevent the liquid rubber from leaking out. 

Larger or more complicated molds are made in pieces 

or with a layer of rubber supported by a plaster shell or 

mother mold attached to a wooden or metal frame. 

Following completion of a successful mold, the original 

model is discarded because it is now possible for it to 

be accurately reproduced. 

Casting the Molds. Casting operations should appear 

clean and efficient. A skillful caster's output can be 

voluminous and often looks effortless as it is being 

produced. Raw materials are close at hand, molds are 

rarely without curing plaster in them, production is 

stored so as not to warp while it is still wet and each 

cycle, from mixing to pouring, setting, and demolding 

is accomplished so as not to waste time or break plaster 

casts. A good caster generally obviates the need for a 

finishing department. 

Two other aspects should be noted. Shipping facilities 

are critical to move the product to the restoration site 

safely. Drawing and design space should be separate 

from the production floor. In summary, the modern 

ornamental plaster shop inevitably looks quite different 

from that pictured earlier in this Preservation Brief (see 

Fig. 1, above), but, with the exception of contemporary 

tools and materials, the operations are the same. The 

following sections discuss how repairs are made by 

today's plaster tradesmen. 

Repairing Historic Ornamental Plaster 

Cornice. A plain run or ornamented plaster {:ornice 

which has undergone damage or severe deterioration 

can often be repaired. Footage which is beyond repair 

should be identified and be carefully demolished to 

expose the underlying structure beneath to which the 

molding was secured. To replace the missing lengths, 

the first step is to obtain a cross-section, or profile, 

through the cornice from finish ceiling to finish wall 

lines. This is best accomplished using one of these 

methods: 

1. A section through the cornice may be determined 

by sawing through the molding, inserting a sheet 

metal blank in the slot and tracing the profile directly on the template. This is considerably more 

accurate than the profile gauge, but will require repointing the saw kerf; alternatively, the cut may be 

made on one of the deteriorated pieces, provided it 

was removed as an intact unit. 

2. The section may be obtained by making a thixotropic rubber impression of the molding, casting the 

result in fresh plaster and sawing through the cast to 

transfer the cross-section to a sheet metal template. 

With t~e section determined, it is drawn onto 22-gauge 

~alvamzed s?eet metal, cut with tin snips and carefully 

filed to the hne. The template is checked periodically 

against the original profile to assure a perfect match. 

With the template blade finally complete, it is nailed to 

stock and slipper (see Fig. 3, above), ready for running 

the replacement footage . 

Short lengths of new cornice are best run on a bench 

using gypsum and lime; the reproduction molding 

shoul~ be somewhat longer than the required length 

(see FIg 18). The new footage is cut and fit in place to 

match the existing cornice, then securely countersunk-

~c~ewed to s~uds, jo~sts and/or blocking. The resulting 

Jomts are pomted WIth flat mitering rods, flush with 

adjacent members (see Fig. 5, above). 

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Longer lengths of cornice may be run in place, much as 

they were historically. Care should be taken that the 

position of the running mold engages with the existing 

work at either end of the run. Yet another method is to 

bench run the cornice to five or six feet, make a rubber 

mold of the model, and pre-cast the replacement parts 

either at the site or in the shop. 

If the damaged cornice is ornamented, samples of the 

enrichment should be removed, making sure that 

whole original units are obtained. This is a difficult 

process, since these units were stuck into plain-run 

recesses called "sinkages" using plaster as an adhesive. 

In order 10 insert a flat chisel behind the ornament to 

break the bond, some units may have to be sacrificed. 

Sacrifice should be minimal. The excised enrichment 

should then be removed to the shop for rubber molding and casting either with or without the paint 

buildup, depending on the demands of the project. 

Whereas molding with several layers of paint make it 

hard to discern new casts from originals, paint-stripped 

molding reveals the remarkable talents of the period 

modelmakers. As noted, contemporary rubber materi10 

Fig. 18. Repairing a Cornice. (a) In the restoration of the Henry 

Hirshfeld House, a 19th century residence in Austin, Texas, removal 

of a tin ceiling revealed a damaged plain-run cornice. Photo: John 

Volz, AlA. (b) A section through the molding was taken, a template 

blade cut, horsed- up, and run on a bench using gypsum and lime. 

Photo: Charles E. Fisher. (c) The new cornice was then cut, fitted, 

and applied to new blocking between wall and ceiling. The external 

miter and returns were pointed using the miter rod. After the ceiling 

restoration was complete, other finishes, such as wallpaper, 

were applied. Photo: Candace Volz. 

als have "fingerprint detail" capability. Modern casts 

are then applied to the new or original runs, again 

using plaster as an adhesive. 

Ceiling Medallion. Ceiling medallions are often in 

greater jeopardy than cornices because the joist-Iathbasecoat support system is susceptible to deflection 

and the force of gravity. The problems of ceiling failure 

are more frequent in the centers of parlors because 

circular-run and shop-cast ornament is often quite 

heavy and was not historically attached with any additional mechanical fasteners such as bolts and screws. 

If the lath or keys have failed, plaster ceiling ornament 

may be saved, in whole or in part, by removing floor 

boards above, then drilling and injecting each lath with 

an elastic acrylic or epoxy material to reattach plaster to 

lath, and lath to the joists. This is a recently developed 

procedure which should only be undertaken by experienced professionals. The consolidation and reattachment process has been used successfully in period 

structures with dramatic results when important plaster 

and painted surfaces would otherwise have been lost. 
Fig. 19. Ceiling medallions may need repair or replacement. The ornamental plasterer takes impressions of the existing plaster, then casts new 

plaster elements. Adhesive plaster is used to reattach the new pieces. Left: Damaged elliptical medallion from Rockland, Fairmount Park, Philadelphia, Pennsylvania. Photo: David Flaharty. Right: Fragments of a medallion from the Bennett House, Charleston, South Carolina. The fragments 

serve as documentation for the replacement medallion. Photo: Peter Sanders . 

. Fig. 20. Repairing a Medallion. Left: The plaster models shown are first lathered with a parting agent (liquid soap). To make a flood mold, 

urethane rubber is poured between wood fences clamped together and dammed with clay. Right: Casting plaster is then spooned into the two-part 

urethane mold. The mold showing six ornaments in the process of being cast is called a "gang mold. " The others are simply single molds. Photos: 

David Flaharty. 

Historic lighting fixtures often hung from elaborate 

ceiling medallions. When these fixtures were later converted to gas and electrical service, the central ornamental plaster canopies were sometimes damaged by 

insensitive tradesmen. More recent adaptive use projects may have caused additional damage. 

Damaged ceiling medallions (see Fig. 19a) can be repaired by carefully removing representative plaster 

ornamentation, molding and recasting in the shop (see 

Fig. 20) and replacing the new enrichments so that 

they align perfectly with the original pattern. Polyvinyl 

acetate bonding agents are applied to the background 

and ornament so that the adhesive plaster grips tightly. 

Alternatively, a severely damaged medallion (see 19b) 

can be replaced using the fragments as physical documentation to cast a visually accurate replacement. 

Sections of plain-run circular molding may also be repaired by determining a section through the run and 

the radius from molding to pivot point. As with cornices, the run should be made on a bench to a length 

greater than required, then cut and fit in place. Circular run sections are installed using plaster adhesives on 

bonded surfaces or modern construction adhesives 

after referring to manufacturers' instructions as to 

whether the adhesive is recommended for use on wet 

or dry materials. Coarse-threaded, galvanized screws 

are often countersunk to aid the bond; if possible, the 

screws should be inserted at points that will ultimately 

be covered with cast enrichments. 

Ceiling medallions frequently appear in matching double parlors. It is not unusual for one ceiling to fail while 

its mate remains undamaged. The flat plastered ceiling 

over the location of the missing medallion often has a 

"ghost;' confirming that a ceiling medallion once ornamented the parlor. The missing medallion may be remanufactured by securing a section, dimensions, and 

samples of cast enrichments from the surviving ornament and accurately following the original procedure 

(see Fig. 7, above). The ceiling on which the new work 

is to be set should be examined for its soundness and, 

if necessary, relathed (with self-furring metal lath) and 

11 
plastered. The pivot point for a circular run is screwed 

into a wooden block, force-fit into the center electrical 

box, and removed after the run is completed. 

After 1850, particularly in the South, ceiling medallions 

were often designed with cast ornament only; no plainrun surround was used. Repair of such medallions 

proceeds as described above but without bordering 

molding. 

An important point needs to be made about adding 

ceiling medallions (or any other kind of ornamental 

plaster element) when there is a lack of historical evidence. If there is no ghost mark or other documentation, indicating a medallion once existed, then the 

room should remain unornamented as it was historically. 

Adding conjectural ornamentation of any type or material (i.e., shop-cast or glass fiber reinforced plaster or 

polystyrene foam substitutes) can create a false sense of 

historical development contrary to the preservation 

principles stated in The Secretary of the Interior's Standards for Historic Preservation Projects. However, if there is 

clear indication that a ceiling medallion once existed, 

but there is inadequate documentation for its replacement, a medallion compatible with the room's historic 

character may be considered. Professional advice 

should be sought. 

Coffered Ceiling. Like cornices and medallions, coffered 

ceilings suffer from poor maintenance practices and 

structural problems; however, these individually cast 

ceiling units are particularly vulnerable when a building is being rehabilitated and great care is not taken in 

executing the work. In the most serious of cases, portions of a roof can collapse, dropping heavy debris 

through the hanging coffering panels, and demolishing 

large portions of the ornamentation (see Fig. 21). 

But even this level of damage can usually be remedied 

by restoration professionals. Immediate action calls for 

shoring the areas adjacent to the damage, and inspecting the hanging apparatus for unforeseen detachment 

Fig. 21. The Yiddish Arts Theater, New York City, c. 1920s. The 

concrete roof of this building collapsed, damaging portions of the 

existing Moorish style coffered ceiling. The square coffer unit was 

easily identifiable and was remaved to a casting shop for reproduction. Photo: David Flaharty. 

12 

and deflection. New channel iron is used to stabilize 

the existing coffers and ties reinforced, as necessary. 

An intact coffering unit is then identified and carefully 

removed to a casting shop for molding and casting (see 

Fig. 22). When re-hung, the units are painted to match 

the historic coffering (see Fig. 23). 

Coffered ceilings appear with plain run or enriched 

cornices. In most cases it is recommended that the 

cornice be repaired first in order to achieve straight and 

level moldings. Then the damaged coffers should be 

replaced with the matching new coffers and the joints 

between pointed. Access from above is critical. 

Finding and Evaluating a Contractor 

When ornamental plaster damage or deterioration has 

been identified, the historic property owner, architect, 

Fig. 22. Repairing a Coffered Ceiling. As part of the theater rehabilitation, the coffered ceiling panels are being reproduced in urethane 

rubber molds and reinforced with open weave burlap and wood fiber. 

Steel channel irons can be seen, attached to the backs of the casts. 

Later, these irons are used to hang the panels from a superstructure 

at the site. Photo: David Flaharty. 

Fig. 23. A pre-cast coffer is lifted into place to abut adjacent panels. 

Tie wire will be fastened to the channel irons and the superstructure 

abave, twisted to level, and finally wadded with wood fiber soaked in 

plaster to prevent the wire from stretching. Photo: David Flaharty. 
or developer should secure the services of a reputable 

restoration contractor before proceeding further. It is 

clear as more and more projects are undertaken, that 

there is a wide disparity of skills within the trade today. This is partly due to the introduction of gypsum 

board as a substitute for traditional plastering. As gypsum board became popular after World War II, plasterers saw the demand for their skills decline. Plastering 

techniques were forgotten because they were often not 

passed down within shops and families. However, 

ornamental plaster studios have seen a resurgence in 

demand for their services in the last decade, particularly as more historic buildings are rehabilitated (see 

Fig. 24). 

Locating an experienced contractor who is suitable for 

your particular project is the goal. First, many professional preservation organizations can provide references for suitable restoration contractors. Local 

plasterers' unions should also be able to identify contractors with experience in ornamental plaster restoration projects. Architects with preservation and 

restoration project experience may recommend contractors they feel have done a good job for them in the 

past. Museums with period rooms have engaged craftsmen to assemble the backgrounds for display of antique furniture and decorative arts. Finally, historical 

societies, either national, state, or municipally organized, may have funded projects which repaired and 

restored ornamental plaster. 

Once several contractors have been identified, their 

specific abilities need to be evaluated. Prospective contractors should be invited to visit the job site to see and 

define the scope of work; written proposals, including 

prices, from all bidders, are essential for comparison. 

References should be provided and investigated. An 

outside consultant may be engaged or an informal adviser designated to aid in evaluating the experience and 

proposals of the bidders. To get a total picture, a completed project should ideally be visited by the prospective client with the contractor present to answer 

questions which often arise. 

Finally, although this may not always be achievable, 

the bidder's studio may be visited, preferably on a normal working day (see A 20th Century Shop Tour, 

above.) Alternatively, the bidder may be visited while 

working onsite. Some ornamental plasterers simply do 

not have shops. They prefer to cast onsite, adhering 

the casts while the plaster is wet, and coordinating the 

job closely with the architect, who inspects each unit as 

it is cast and before it is installed. 

Conclusion 

Decorative plasterwork is usually a component of the 

historic character of interiors and, consequently, The 

Secretary of the Interior's Standards for Historic Preservation 

Projects call for its protection, maintenance, and repair. 

Where decorative plasterwork has deteriorated beyond 

repair, it should be replaced to match the old. Based on 

physical documentation, both repair and replacement 

can be accomplished using traditional molding plaster 

Fig. 24. This plaster studio is well organized, with ample work 

space. Note the plaster casts hanging neatly on the wall. Photo: 

Berry and Homer, Philadelphia. 

and casting procedures, together with the best of the 

modern molding materials available. Once a "lost art" 

after the Depression years, the skills of today's ornamental plasterers are increasingly in demand as part of 

historic preservation project teams. The ingenious and 

inspired decorative work created by our earlier architects and artisans can now be assured an extended life. 

l3 
Bibliography 

Bankart, George. The Art of the Plasterer. London: B. T. Batsford, 1908. 

Dalton, Byron William. Practical Plastering and Cement Finishing and 

Related Subjects. Chicago, Illinois: Byron William Dalton, 1949. 

Flaharty, David. "Ornamental Plaster Restoration." Fine Homebuilding. 

No. 57, December, 1989/January 1990, pp. 38-42. 

Garrison, John Mark. "Decorative Plaster: Running Cornices." The 

Old-House Journal. Vol. XII., No. 101, December, 1984, pp. 214-219. 

_____ . "Casting Decorative Plaster." The Old-House Journal. 

Vol. XlII, No.9, November, 1985, pp. 186-189. 

Gypsum Construction Handbook. Chicago, lllinois: United States 

Gypsum Co., 1986. 

Harris, Cyril M., editor. Illustrated Dictionary of Historic Architecture. 

New York: Dover Publications, 1983. 

Millar, William. Plastering, Plain and Decorative. London: B. T. 

Batsford, 1897. 

Phillips, Morgan. "Adhesives for the Reattachment of Loose Plaster;' 

Association for Preservation Technology Bulletin, Vol. XlI, No. 2, 1980, 

pp.37-63. 

Van den Branden, F. and Hartsell, Thomas L. Plastering Skills. 

Homewood, Illinois: American Technical Publishers, Inc., 1984. 

Acknowledgements 

Thanks go to the technical experts in the field who reviewed and commented 

upon the draft manuscript: M. Earle Felber, Andrew Ladygo Oefferson Poplar 

Forest}, Lee H. Nelson, FAIA, Gilbert Wolf (National Plastering Industries), and 

Stephen Zychal (Ornamental Plastering, Inc.). Insightful comments were 

offered Gary L. Hume, Acting Chief, Preservation Assistance Division, Karen 

Kummer, Small Homes Council-Building Research Council, University of 

Illinois, NPS cultural resources program regional offices, and the staff of 

Technical Preservation Services Branch, H. Ward Jandl, Chief. Old-House Journal 

and Fine Homebuilding were most generous to grant permission to use photographs from their publications. Kay D. Weeks is credited with coordinating 

this cooperative publication project and general editorship. 

This publication is not copyrighted and can be reproduced without penalty. Nonnal procedures [or 

credit to the author and the National Park Seroice are appreciated. October, 1990. 

14 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402