How Does Water Affect Plaster Walls vs Drywall?

Plaster is a hard, mineral-based coating over wood or metal lath. Water often seeps through cracks or porous spots, traveling behind the plaster layer before it shows on the surface. This can delay detection, sometimes for a long period. Drywall has a porous gypsum core sandwiched between paper facings. Water soaks directly into the core, causing it to swell and weaken much faster than plaster might, often within hours.

The main risk with plaster is hidden decay. Water trapped behind it can rot wooden lath or corrode metal lath, compromising the wall's support. You may not know until a section collapses. With drywall, the wet core loses all strength. A soaked ceiling drywall panel can become heavy and fall, creating a safety hazard and spreading debris. In either case, the longer the water sits, the greater the risk to your home's structure.

Plaster repair is often a specialized skill, requiring matching the old texture and composition. It can be a multi-step process of layering. Drywall repair is generally more straightforward, involving cutting out the bad section and patching in a new piece. For significant damage in either material, the pros may recommend removing large sections to ensure structural integrity and prevent future mold.

• For plaster: The damaged section is cut out, the lath is assessed and replaced if rotten, and new plaster is applied and blended.
• For drywall: The wet portion is cut away, new drywall is installed, taped, mudded, sanded, and painted to match.
• In both cases, the source of water must be fixed first.
• The area must be completely dry before any repair begins.
• Mold remediation may be needed before reconstruction.
• Matching textures and finishes can be a skilled part of the job.