Water damage can cause serious problems for your home, and it's important to know how to repair water-damaged plaster. Gypsum that has become wet is best repaired with a setting-type joint compound, also known as mud. The ready-mixed compound will not be hard enough and is vulnerable to any residual moisture in the wall material. To repair damaged wall plaster, you must first assess the damage, repair the source of the damage, remove the old plaster, and apply a joint compound to repair the cracks.
Identifying water damage is relatively easy. Paint and water are insoluble and an easy way to identify if the plaster is damaged by water is to look for peeling paint or air bubbles that burst and flake. Additionally, water damage usually causes streaks and stains on walls and ceilings that vary in color from dark yellow to brown. If you notice a brown stain on your plaster walls, bubbles or flakes, it is likely that your plaster walls or ceilings have been damaged by water.
Before repairing the plaster, make sure that the underlying cause of the water damage has been thoroughly and properly treated. If the damage is not extensive (small holes and cracks are observed), it is quite easy to apply patches. Pre-mixed putty compounds, which come in small tubs, work well for this. Use a spatula to apply the material to all damaged areas.
Wipe off excess with a damp cloth or sponge and allow to dry. If the product shrinks as it dries, apply another layer. For larger holes or cracks, it may be necessary to first apply a layer of fiberglass mesh tape to provide support. Apply the patch to the tape. Continuously letting the plaster get wet will allow water to seep into the inside of the wall, damaging the wood and other structures behind it.
Over time, water can be absorbed from the masonry of the foundation (or into the outer stone walls) and damage any plaster applied to it. It would be best if you looked for signs of water damage, such as peeling paint, water stains ranging from yellow to brown, fallen and peeling plaster and, in the worst case, mold. Using a bucket of clean water and a sponge, wash the surrounding area as a final cleaning exercise, and then let the water-damaged plaster wall dry completely. As homeowners assess Hurricane Ida's damage, it's important to remember that many historic materials, such as gypsum, are resistant to water damage and can (and should) be repaired.
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