Drywall vs. Plaster: How to Tell What You Have

If your home was built before roughly the 1950s, your walls may be plaster rather than drywall — and the difference matters, because the two materials repair completely differently. A plaster wall patched with drywall tape and joint compound tends to crack around the edges of the repair within a season or two.

Three quick tests

• The push test. Press firmly on the wall between studs. Drywall gives slightly. Plaster is rock-hard and does not move at all.
• The pushpin test. A pushpin goes into drywall with light thumb pressure. It will barely dent real plaster.
• Look at an outlet or switch. Remove a cover plate. If you can see a thin layer over thin wooden strips (lath), that is plaster. A single uniform panel roughly half an inch thick is drywall.

Why it changes the repair

Plaster and drywall move differently and bond to different things. Plaster is applied wet over lath and cures hard; drywall is a manufactured panel finished with tape and compound at the seams. When you repair a plaster crack with drywall products, the rigid plaster on either side and the more flexible compound in the middle expand and flex at different rates, and the joint between them fails. That is why the crack comes back at the edge of the patch.

Plaster repair done right involves stabilizing the existing plaster (it often has failed keys behind the lath), and using materials compatible with plaster's hardness and movement. It is a genuinely different skill from drywall finishing.

The mixed-house complication

Many older Wisconsin homes are both. A house updated over the decades often has drywall in the rooms that were renovated and original plaster in the ones that were not — sometimes within a few feet of each other. This is why a contractor should look at the actual wall before quoting a repair, rather than pricing from a photo. What looks like a simple patch can turn out to be plaster work.

Should you replace plaster with drywall?

Sometimes. If plaster is extensively cracked or has lost its keys over large areas, removing it and re-boarding in drywall can be more cost-effective than repeatedly repairing it — and gives you a chance to add insulation and update wiring while the wall is open. For sound, localized damage, proper plaster repair is usually the better value. Both are legitimate; the right answer depends on the condition of the wall.