Need to tackle some plaster repair? Flat plastering is a time-honored, magical craft, the process of mixing dry powders and water into wet, plastic mortar, then spreading it over entire walls so that it creates a surface that is die-straight and alabaster smooth. Skill and handed-down trade practices are the secret ingredients in traditional plaster, and they help make it a durable, original, and beautiful finish that old-house owners go to great lengths to keep. In contrast, flat plaster repairs are usually much smaller and more variable, with techniques adapted to the many kinds of damage and decay, from tiny cracks to large holes, and through hard-won experience. Though being handy comes into play here, too, repairs often gain as much from clever products specifically made to improve the results and assist the ad hoc plasterer. What we’ll explore here is an overview of these methods and materials to explain what’s possible with plaster repairs and how they can help you retain the solidity and beauty of three-coat plaster walls and ceilings.
Historic plaster walls that have stood up well for decades can start to fail for a number of reasons. Pre-industrial plaster from the 1850s or earlier may be affected by shortcomings in the materials themselves, such as lime of uneven quality or sand that contains impurities. A more likely cause, though, is dicey installation conditions, such as plastering in weather that is too hot or humid (which can keep the plaster from setting) or too cold (which causes the plaster to freeze before it can cure). Then there’s just the toll of time—movement of balloon framing, for instance, or roof leaks that saturate a ceiling or wall, stressing the plaster and lath with the added weight of water while leaching out binding materials.