Cast architectural ornament : plaster and compo

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Reid, Bronwyn
Spodek, Jonathan C.
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Thesis (M.S.H.P.)
Department of Architecture
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Plaster and compo are both materials used for cast architectural ornamentation. Preserving, repairing, and in-kind replacing cast architectural ornamentation is necessary to maintain the integrity of a space. Plaster and compo are visually and texturally very similar materials. Compo was invented to be a less costly substitute for plaster. Whereas the two materials are easily mistaken for one another, they are chemically quite different. The ingredients and methods used to create the two separate materials exemplify this difference. Understanding the differences is key to successfully preserving the ornaments and, thus, the spaces in which they are located. Repairing plaster with compo or compo with plaster can lead to the destruction of cast architectural ornaments. Furthermore, chemical paint removers that are safe to use on plaster can deteriorate compo. It is necessary to thoroughly understand the nature of the materials so that informed decisions can be made about their treatments. The study addresses the similarities and differences, the maintenance, deterioration, repair, and replacement of the two materials.