First, the water softens the plaster and it begins to loosen. If steps are not taken to dry the plaster and remove all this moisture, it quickly becomes damp, which turns into mold. Gypsum boards can also get wet due to conditions in which they absorb large amounts of moisture from the air. This can include constant high humidity caused by environmental conditions or, possibly, by nearby standing water, combined with poor ventilation.
Paint and water are insoluble, and an easy way to identify if plaster is damaged by water is to look for peeling paint or air bubbles that explode and peel off. Water-damaged plaster can have serious health consequences and is often indicative of potential damage that can damage the overall integrity of the structure. Before repairing the plastering, be sure to thoroughly and adequately address the underlying cause of the water damage. Using a bucket of clean water and sponge, wash the surrounding area as a last cleaning exercise, and then allow the water-damaged drywall to dry completely.
Over time, water can creep up from the foundation masonry (or inward from exterior stone walls) and damage the plaster that has been applied to it.