Why Does Plaster Hold More Moisture Than Drywall After Water Damage?

Traditional plaster is a dense, hand-applied material, often over wood or metal lath. This creates a thick, solid barrier with fewer air pockets. Modern drywall, or sheetrock, is a manufactured panel of gypsum sandwiched between paper facers. The gypsum core is relatively porous, but the entire assembly is thinner and more uniform, allowing for different drying characteristics when wet. Understanding these material differences helps explain why they react so differently to a leak or flood.

Drywall absorbs water quickly, often swelling and becoming soft. However, its paper facing and porous gypsum core allow moisture to evaporate more easily when exposed to air movement. Standard drying equipment can pull moisture directly from the panel's surface. While wet drywall often needs replacement, the drying process for salvageable areas is typically more straightforward than for plaster systems, primarily because the wall cavity is more accessible for drying air.

For plaster walls, the pros use specialized moisture meters and often create inspection holes to check the cavity. They may need to remove baseboards or small sections to insert drying equipment like injectidry systems behind the wall. The goal is to create airflow in the concealed space to dry both the plaster and the lath system effectively. This careful process helps preserve the wall's structure and prevent the hidden risks of trapped moisture.