Category Comparison
Drywall vs Plaster: How to Tell Which You Have
February 8, 2021 7 min read By ConroeDrywall team
Two different ways to build a wall
Plaster is a wet system applied in layers on site. Coats of plaster are worked over a backing — traditionally wood lath, later metal lath or gypsum board — and build up to a hard, dense, monolithic surface with no joints in it.
Drywall is a dry system. Gypsum panels are manufactured flat, fastened to the framing, and the only wet work is treating the joints between them. That difference in method is the source of every other difference between the two.
Around this region plaster is uncommon and concentrated in older stock — the historic cores of towns like Huntsville and Montgomery, and a scattering of pre-war houses. Most of what people call plaster in newer housing is actually drywall with a heavy texture.
Telling them apart
The pin test is the quickest. Push a pin or thumbtack into a hidden spot. Drywall takes it with gentle pressure. Plaster resists, and may chip rather than accept the point.
Knocking helps too. Plaster returns a dense, solid sound; drywall sounds comparatively hollow between the studs. And raking light is diagnostic on drywall, since it reveals the faint grid of taped joints that a monolithic plaster wall simply does not have.
How each fails
| Plaster | Drywall | |
|---|---|---|
| Typical failure | Cracking, keys breaking, sections detaching from lath | Joint cracking, nail pops, impact holes |
| Water response | Softens and can crumble; may survive minor exposure | Wicks water, paper facing feeds mold |
| Repair skill | Specialist; matching texture and hardness is difficult | Ordinary trade skill, widely available |
| Repair speed | Slow, multiple cure stages | Faster, though still cure-limited |
| Sound damping | Better, from mass and density | Weaker unless assembly is designed for it |
| Curved and shaped work | Follows curves readily | Requires special board or scoring |
Plaster’s distinctive failure is losing its keys. On a lath system, the plaster squeezes through the gaps between lath strips and hardens into hooks behind them. When those keys break, a section separates from its backing and moves when pressed, even if the surface still looks intact. That is a different problem from a crack and is not solved by filling the surface.
Repairing plaster
Plaster repair is genuinely specialist. A patch has to match hardness, thickness and texture, and drywall compound over plaster often fails at the boundary because the two materials move differently.
Where plaster is sound but cracked, it can usually be stabilised and patched, and that is normally the right answer for an older house with character worth keeping. Where the keys have gone across a large area, the wall is failing structurally as a surface and patching is not the answer.
Should you convert?
Converting plaster to drywall is a heavier job than it appears, and it is worth being clear-eyed about why you would.
Good reasons: the plaster has failed extensively; the walls are being opened anyway for rewiring, plumbing or insulation; or the surface has been patched so many times that it no longer reads flat.
Poor reasons: it is old; or drywall is assumed to be an upgrade. Sound plaster is a good wall, and it is harder and better at damping sound than drywall is.
If you do convert, expect three things. Removal generates a great deal of heavy debris, considerably more by weight than a drywall tear-out. The lath usually comes out with it. And the framing behind is frequently irregular by modern standards, so furring or shimming to bring it into plane is normally part of the work rather than an extra. See drywall replacement.
The practical case for drywall
For new work and for most remodelling the decision is already made, and repairability is the reason. A drywall wall can be opened, altered and closed by any competent contractor, patched with materials from any supplier, and finished to match in a day or two.
That matters more over the life of a building than the qualities plaster wins on. Walls get opened for wiring, for plumbing, after leaks, and when rooms change use — and a wall that is easy to open and close honestly is worth a lot. For what installation involves, see drywall installation.