Can You Put New Drywall Over Old Plaster? What to Check First

Yes, you can drywall over plaster in many cases. New 1/2 inch board is screwed through sound plaster and lath into the framing, as long as the surface is solid and flat and you plan for the extra thickness at trim and outlet boxes. Paneling, popcorn ceilings and ceiling tiles follow similar rules. In an older Ontario home, test textured ceilings and plaster for asbestos before you cover or disturb anything.

Can you drywall over it? A quick answer by surface

Covering an old surface saves demolition, dust and disposal. It also costs room thickness, buries problems and does not suit every wall. Here is the short version, with detail below.

Can you drywall over plaster and lath?

Yes, when the plaster is sound. Walk the wall and check four things before you buy a single sheet.

• Is it attached? Tap with your knuckles. A hollow, drummy sound or a bulge means the plaster keys, the blobs pushed between the lath strips, have broken. Small loose areas can be pulled tight with screws and plaster washers. Large ones are better cut out.
• Is it dry? Stains, soft spots and powdery plaster mean moisture. Fix the leak or condensation first.
• Is it flat? New board follows the shape underneath. Shim low spots or add furring strips on badly wavy walls.
• Can you find the framing? Plaster and lath fool most stud finders. Locate studs and joists by their old nail lines, a magnet or a small probe hole.

Fasten into the framing, not into the lath or plaster alone. Screws must pass through the plaster, the lath and the new board and still bite well into the wood. Adhesive on its own is not enough. Many installers use 1/2 inch board for the overlay, and some drop to 3/8 inch on walls to keep the added thickness down. Check the sheet label for the framing spacing it is rated for, especially on a ceiling.

If the plaster is only cracked, repair can be a better choice than covering it. The guide to repairing old plaster walls and the comparison of lath and plaster vs modern drywall help you decide.

Test for asbestos first in older homes

Ontario's asbestos page says the material is commonly found in buildings constructed before 1986, and lists drywall compound among the products it typically appears in. Older layers can hide under newer repairs, so treat anything built or repaired before about 1990 as unknown until it is tested.

You cannot tell by looking. A qualified consultant takes samples, and a lab confirms whether asbestos is present. Do not scrape, sand or drill a ceiling to see what is inside.

Here is where the rules sit. The Ontario regulation does not apply to the owner of a private home who lives in it, but it does apply to the contractors, employers and workers on a private project. A contractor will therefore ask whether the material has been tested, or will treat it as asbestos. Where the regulation does apply to the owner, the owner must list designated substances such as asbestos at the site and share that list with contractors before they sign.

Covering is not automatically safe either. Screws and preparation disturb the material underneath, and the next renovator will meet it later. If a test is positive, ask the consultant about the options for your condition and project, and keep the report. The post on asbestos in old ceilings goes deeper.

What an overlay does to trim, outlets and room size

An overlay adds the thickness of the new board to every wall. On a 1/2 inch board that is about 13 mm, and it shows up in places people forget:

• Window and door jambs end up recessed and need extensions.
• Casings and baseboards come off and go back on, or get replaced, over the new surface.
• Outlet and switch boxes sit behind the new face and need extensions. This is electrical work. In Ontario, hired electrical work is done by a Licensed Electrical Contractor under Electrical Safety Authority rules.
• Registers, thermostats and stair walls need re-setting or trimming.
• Plaster cornices and ceiling roses in older homes are hard to cover and are often better kept and restored.

Ceiling overlays also cost about the same 13 mm of height, and light fixtures and smoke alarms need re-fitting. Walk every wall with a notepad before you order, and list each window, door, box and register.

Can you drywall over wood paneling?

Often yes, especially the thin 1960s and 1970s sheet paneling. It must be solid and fastened to studs. Tap it, and press on the seams to find loose spots.

Screw through the paneling into the studs, and do not rely on adhesive. Grooves do not show through 1/2 inch board when you fasten it tight. An overlay is especially handy when the paneling is glued to a wall that would tear when you pull it off. It is a poor idea when the paneling is loose, bulging or hanging on strapping over a damp wall.

Look behind the paneling before you cover it, especially in a basement. Loosen one panel and check for dampness, mould, stained framing or old insulation. Paneling can hide a moisture problem for years. New board over a damp wall will only hide it again.

If the room only needs a refresh, painting the paneling is also an option, and it avoids the thickness change altogether.

Can you drywall over a popcorn ceiling or ceiling tiles?

Popcorn ceilings. Test first. If the texture is asbestos-free, you can scrape and skim it or cover it with new board screwed into the joists. Covering keeps dust down, but the board rocks on the lumps, the screws must land in the joists, and you lose about 13 mm of ceiling height. Texture that is flaking or very thick will not let the board seat flat, so scrape it first. If the test is positive, do not do either yourself. The guide to popcorn ceiling removal covers the removal path.

Ceiling tiles. Older tiles and the glue behind them are another material to test before you disturb them. Many tiles are stapled to thin wood strips that cannot hold drywall, so the new board has to be screwed into the joists, which the tiles hide. Often it is simpler to take the tiles and strips down once testing is clear, then board the ceiling properly. Stains on tiles mean a leak above, and that gets fixed first.

Ceiling sheets are heavy and awkward. Use a panel lift and a second person.

Fire rating, permits and when to remove the old surface instead

If the wall is part of a fire separation, such as the wall between the house and an attached garage or between units, the rating belongs to the whole assembly, and a thin overlay may not match it. Type X board in 5/8 inch is the usual choice where the code requires fire-rated drywall. See when you need fire-rated drywall. Check with your municipality's building department before changing a separation, and ask whether anything in your project needs a permit. Covering walls is usually cosmetic, but moving boxes, adding insulation or opening walls can change the answer.

Take the old surface off instead when plaster is loose or damp, a wall needs new wiring, plumbing or insulation, the surface is badly out of flat, the room cannot spare the thickness, or an asbestos assessment recommends removal. Removal is dusty and heavy work with its own disposal rules, so plan containment.

D&D Interior Services does drywall and plastering across Kitchener-Waterloo, Cambridge and Guelph, and the free written quote lists the visible drywall work separately from any plumbing, electrical or structural scope. Start with the drywall and plastering service page.

Drywall-over-existing-surface questions

Can you drywall over lath and plaster?

Yes, if the plaster is solid, dry and reasonably flat. Screw the new board through the plaster and lath into studs or joists, using screws long enough to bite into the framing. Loose or crumbling plaster should be secured or removed first, and homes built before about 1990 should be tested for asbestos.

Can you drywall over a popcorn ceiling without removing it?

It can be done once the texture has been tested and found asbestos-free. The board is screwed into the joists through the texture and loses about 13 mm of ceiling height. Flaking or thick texture should be scraped first. If asbestos is present, do not disturb it and ask a qualified consultant for options.

Can you drywall over ceiling tiles?

It is rarely the easy choice. Tiles are often stapled to thin strips that cannot hold drywall, so the screws must reach the joists. Older tiles and their glue should be tested for asbestos first. Once testing is clear, taking the tiles and strips down and boarding the ceiling is usually simpler.

What thickness of drywall should I use over plaster?

Half inch board is the common choice, and some installers use 3/8 inch on walls to limit the added thickness. Use 5/8 inch Type X where the code needs a fire-rated assembly. Check the sheet label for the framing spacing it is rated for, particularly on ceilings, and confirm with your building department.

Devon Moore, Operations Lead Co-Founder & Operations Lead — D&D Interior Services

Devon Moore is the co-founder and Operations Lead at D&D Interior Services, delivering kitchen renovations, bathroom renovations, flooring, and interior upgrades across Waterloo Region.