American Conservation Consortium

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Light bleached paint, c. 1840.

Conservation Treatment of Interior Architectural Features

Dirty and cleaned linoleum, c. 1890.

American Conservation Consortium provides treatment of a wide variety of interior architectural features.  The materials comprising these are the same as for wooden objects, so our wealth of experience and knowledge can assist you with your architectural projects as well.  While limited only by imagination, typical projects include the following.

bulletTreatment of light-damaged paint.  Often, painted woodwork and paneling has been degraded and bleached by light.  We have developed treatments that often can return much of the color back to the paint, while at the same time preserving it.
 
bulletReattachment of lifting paint.  In-painting of paint losses, including decorative and fancy paint.  Removal of later paint from original paint.
 
bulletAnalysis of paint, including microscopic cross-sectioning and pigment identification.  Creation of custom paint formulas using historic pigments, including reversible/removable paint systems.
 
bulletTreatment of finishes, including consolidation, removal of later finishes, and application of new finishes.
 
bulletCleaning surfaces of all types of dirt and grime.  Application of protective removable coatings.
 
bulletWooden structural repairs of all kinds to paneling, moldings and interior features.  Gluing of splits and breaks, replacement of losses, in-coloring fills, and replication of missing elements.
 
bulletStabilization treatment of cracked historic plaster surfaces using our custom-developed procedures, with either our own staff or by providing training and support to your crew.
 

The following information provides more detail on plaster stabilization.

Originally, hair was added to historic plaster to act as an interlocking agent, tying the other loose, brittle components together into an integrated whole. Without this hair, the plaster elements would crumble with relatively minor pressure.  In plaster surfaces that maintain their integrity, this reinforcing hair creates a single sheet of plaster, much like a giant cross-linked molecule, capable of remaining in place an indefinite length of time. However, a crack indicates that the strength of the interlocking hair has been exceeded, and the hair has broken, resulting in an integrity loss to the sheet of plaster.

Historic plaster on wooden lath has a subtle undulation and waviness that corresponds to the shape of the lath beneath it. This subtle ripple effect, that can be see easily in raking light or felt by running a hand over the surface, is the defining characteristic of original plaster from the 18th and 19th centuries. Replastering does not achieve this effect, so the delicate nuance of the wall and ceiling surfaces is lost forever with the removal of original plaster. Similarly, treatments that result in skim coating the plaster also destroy this defining characteristic. For these reasons, it is desirable to develop a treatment system for cracked plaster surfaces that maintains the nature of the surface yet reintroduces integrity to the plaster.

The traditional method of repair for plaster cracks is to open up the cracks in an undercut manner, fill the cracks with a gypsum/perlite plaster, and level the fills. This process does not re-create the fibrous bridge of the cracked area that was originally provided by the hair, and the crack may re-open with movement of the wall due to seasonal changes or subtle shifts of the building. If the network of existing cracks is sufficiently large, this traditional repair method would result in excessive disruption of the plaster. For this reason, often the historic plaster is removed and the area is re-plastered with gypsum/perlite plaster. These types of treatment processes result at best in a significant degree of invasiveness to the plaster, and at worst, in complete loss of the original plaster.

American Conservation Consortium has developed a system that is based upon the common conservation practice of facing painted surfaces. A thin, long-fiber membrane is adhered to the plaster surface, effectively bridging the cracks and returning the integrity of a single sheet of plaster. This imitates the original inclusion of hair in the plaster mix. By choosing both the adhesive and the membrane to be flexible, a certain amount of movement of the cracks is possible without them reappearing. Additionally, the flexibility allows the membrane to conform to irregular surfaces. This system has been applied to 18th and 19th century plaster with excellent results. In general, the plaster surfaces in the Dwelling House are relatively smooth and are excellent candidates for this treatment system.

Each plaster surface is different, and therefore the specific combination of membrane and adhesive will vary. However, typically, all surfaces in a room, or even a building, will receive the same type of treatment, although there can be certain rooms that require different approaches in different areas. Typically, membrane thicknesses are around 1 mil, so that the membrane will be fully incorporated within the equivalent of several coats of paint. Properly applied, the membrane is completely invisible once the treatment has been completed. All of the subtle undulations of the plaster are maintained. And, most importantly, the original plaster has been preserved.

The combination of adhesive and membrane depends upon several factors. First and most important is how the membrane reacts to the adhesive. The second factor is the nature of the plaster surface. Bare plaster will allow the use of most adhesives, as will older oil paint. However, certain paints such as whitewash or calcimine, can create adhesion problems and require special preparation as part of the treatment.  Thus, a treatment of a specific plaster surface is a balance between the nature of the plaster/paint combination, the amount of time to be spent on surface preparation, the desired membrane, and the appropriate adhesives.  And, of course, the skill and experience of the treatment crew is of paramount importance.

This system is not designed for plaster that is heavily detached from the lath, and is not a substitute for injection stabilization processes.  However, it will stabilize a surprising amount of plaster detached from the lath if surrounding plaster is still well attached.  Envision the process as similar to a stretched head skin on a drum.  The tension created will support a large amount of weight.

American Conservation Consortium has done extensive testing of various adhesives, membranes and procedures to develop a system of plaster stabilization that is highly effective.  We would be glad to provide treatment services with our staff for smaller projects, or we will train and manage your staff for larger projects.

 

 

 

 

 

 

 

 

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American Conservation Consortium. Ltd.

4 Rockville Road, Broad Brook, CT 06016, 860-386-6058, acc@conservator.com

Copyright 2008, American Conservation Consortium, Ltd., all rights reserved