Walk into a Victorian in San Francisco, an Edwardian flat in Oakland, or a 1920s bungalow in the East Bay, and the walls are probably not drywall. They’re plaster over lath: thicker, harder, and a lot more work to fix than the drywall in newer homes. When a crack opens or a ceiling starts to sag, homeowners hear three different answers: patch it, cover it, or rip it all out. The right one depends on what’s behind the paint, and on what the wall might contain.

This guide covers how the two systems are built, how to tell which one you have, what goes wrong with old plaster, and how to decide between repairing, covering over, and replacing it. It also includes national cost ranges from published sources and the lead and asbestos rules that apply before anyone opens a wall.

How drywall and plaster are built

Traditional plaster

According to the National Park Service’s Preservation Brief 21, plaster was the wall surface used in nearly all buildings until the 1930s or 40s. Historic plaster was usually applied in three coats over lath:

• Scratch coat: pushed through the gaps in the lath so it curls behind and forms “keys” that hold the wall on.
• Brown coat: builds thickness and flattens the surface. The scratch and brown coats each ran about 3/8 inch thick.
• Finish coat: a thin, hard layer, about 1/8 inch, troweled smooth.

The lath came in three main types: narrow wood strips, expanded metal mesh, and rock lath (gypsum board panels made as a plaster base). The same NPS brief notes rock lath was in use as early as 1900, and by the late 1930s it was used almost exclusively in residential plastering. Older wood lath walls tend to be the thickest: the brief puts minimum plaster thickness at about 3/4 to 7/8 inch on wood lath, 5/8 inch on metal lath, and 1/2 inch on rock lath.

Drywall

Drywall (gypsum board) is a gypsum core faced with paper, delivered in 4×8-foot and larger sheets. Crews screw it to studs or joists, tape and mud the joints, and sand to the finish level the room needs. There’s no wet base coat to cure, so it goes up faster and needs less specialized labor, which is a big reason it took over from plaster in newer construction. Standard residential walls are typically 1/2-inch board. If you’re new to finish levels, our guide to drywall finish levels explains the difference between a basic taped wall and a fully smooth one.

Drywall vs plaster at a glance

Neither material is simply “better.” Plaster wins on hardness and feel. Drywall wins on cost, speed, and how easy it is to change later: running new wiring, adding a doorway, or opening a wall for plumbing.

How to tell which one you have

If your house was built before World War II and the walls haven’t been redone, assume plaster until you confirm otherwise. Quick checks:

• Knock on it. Plaster sounds solid and dull. Drywall between studs sounds hollow.
• Try a pushpin. It slides into drywall with thumb pressure. On plaster it barely goes in.
• Look at an outlet. With the power off and the cover plate removed, look at the edge of the wall opening. Layered, gritty material points to plaster; a paper face over a white core points to drywall.
• Check the attic or basement. Where framing is exposed, you may see wood lath strips with plaster keys squeezed between them.
• Look for mixed walls. In older homes it’s common for one room, or one wall, to have been replaced with drywall during a past remodel while the rest stays original.

Why old plaster cracks

Plaster is rigid, so it shows every movement in the house. The NPS brief lists the usual causes:

• Settlement and vibration. Houses shift as clay soils swell in the rainy season and shrink in the dry one. Diagonal cracks running in opposite directions are the classic sign, and they often start at door and window corners.
• Lath movement. Wood lath absorbs moisture and expands and contracts as humidity rises and falls, which often shows up as horizontal cracks that return year after year.
• Structural deflection. Undersized framing, or an old remodel that cut in an opening without a proper header, lets the structure sag over time.
• Broken keys. When the keys behind the lath snap, the plaster loses its grip and starts to bow. On ceilings this is the one to take seriously: the NPS notes that if it isn’t repaired, chunks of plaster can eventually fall.
• Water. Long-term leaks soften plaster and rot lath. After a leak, the source has to be fixed first. Our article on water stains on the ceiling walks through that sequence.

The brief doesn’t address earthquakes, but in the Bay Area seismic shaking is one more source of the movement that rigid plaster can’t absorb.

Repair, replace, or cover over: how to decide

The deciding question is not how bad the wall looks but whether the plaster is still firmly attached. A wall covered in hairline cracks can be perfectly sound. A wall that looks fine can have a ceiling panel hanging on by a few keys. Press gently with a flat palm: if a section moves, flexes, or sounds hollow and crunchy, it’s loose.

When repairing plaster makes sense

Repair is the default for sound plaster, and it’s what the NPS recommends for historic homes: plaster “is often not as badly damaged as it first appears.” Hairline cracks can be filled with joint compound or patching plaster. Cracks that keep coming back get widened slightly, then bridged with fiberglass mesh tape and several coats of compound. Loose areas surrounded by good plaster can be pulled back to the lath with screws and plaster washers, then taped over. Small holes are often patched with a piece of drywall shimmed flush to the old surface, then finished to blend in.

Repair keeps the thick, solid wall, the original trim lines, and the character of the room. It usually costs the least when damage is limited to a few areas.

When covering over makes sense

If the plaster is attached but the surface is a patchwork, covering it is often smarter than demolishing it. There are two common ways to do it:

• Skim coating: thin coats of compound over the whole wall to create one flat, uniform surface. It works when the plaster is sound and the problem is appearance.
• Laminating new board: thin drywall screwed through the plaster into the framing, then taped and finished. The NPS describes a related method for cracked or sagging historic ceilings that aren’t water-damaged: wood furring strips screwed through the old lath and plaster, one to each joist, then new lath and plaster over them. It notes the approach “creates much less dust than demolition.”

Covering adds some thickness, so outlet and switch boxes usually need extension rings (electrician work), and deep window and door trim may sit closer to the new wall surface. When the plaster itself is failing, covering only hides the problem.

When tearing out makes sense

Full removal is justified when the plaster is loose over large areas, badly water-damaged, or when the walls need to come open anyway for new wiring, plumbing, insulation, or seismic work. At that point, replacing the surface with drywall usually costs less than rebuilding plaster, and it makes future work easier.

Two alternatives are worth knowing about if you want the plaster look back. A licensed plastering contractor can replaster over new metal or rock lath, or install veneer plaster: gypsum “blueboard” panels finished with a thin, hard plaster coat. The NPS describes veneer as less expensive than a two- or three-coat plaster job but only slightly more expensive than drywall. Its two-coat version is rated at 1,500 psi, and the finished wall “looks more like traditional plaster than drywall.”

What each option costs

These are published national ranges, not quotes. Every job depends on access, ceiling height, how much trim has to be protected or reset, and what testing turns up.

Adding Fixr’s wall removal range to HomeAdvisor’s installation range gives a rough national figure of about $3.60 to $6.70 per square foot of wall to tear out plaster and hang new drywall. That’s before painting, trim work, electrical box changes, or any hazardous-material testing. Set against skim coating at $1.10 to $1.30 per square foot, it shows why a sound but uneven wall is usually cheaper to skim than to replace. Spot repairs priced per square foot run much higher, which is why they make sense only when the damage is confined to a few areas.

Expect Bay Area numbers to run higher than national averages because labor dominates this work. In the Bureau of Labor Statistics’ May 2025 wage survey, drywall and ceiling tile installers in the San Francisco–Oakland–Fremont metro area earned a mean of $43.79 an hour (BLS OEWS, metro area), against a national mean of $30.58 (BLS OEWS, national).

Before anyone opens a wall: lead and asbestos

Old plaster walls carry more than plaster. Test before you sand, cut, or demolish:

• Lead paint. EPA’s Renovation, Repair and Painting rule applies to paid work that disturbs paint in homes built before 1978. Only minor repair and maintenance that disturbs six square feet or less of paint per room inside is exempt, and demolition never qualifies (EPA). A crack repair can stay under that limit; skim coating a room or tearing out a wall won’t. Ask anyone disturbing painted surfaces in a pre-1978 home whether they’re RRP-certified.
• Asbestos. The Consumer Product Safety Commission notes that older patching compounds used on wall and ceiling joints, and textured paints, may contain asbestos, and that their use was banned in 1977 (CPSC). The NPS brief adds that asbestos, used mid-century as an insulating and fireproofing additive, may be present in old plaster itself. CPSC’s advice for material in good condition is to leave it alone; testing matters when the material will be disturbed.
• Who removes it. California separates two credentials: the CSLB asbestos certification, which limits a contractor to asbestos work within its own licensed trade, and the C-22 Asbestos Abatement classification for contracting abatement as its own job. CSLB also ties the C-22 to current registration with Cal/OSHA’s Division of Occupational Safety and Health (CSLB). New Line Drywall does not do abatement. If a test comes back positive, an abatement contractor handles removal first, and the drywall work follows.

Common mistakes with old plaster

Crews working in older houses see the same problems again and again:

• Taping over a moving crack with paper tape and a single coat. It looks fine for a season, then the crack telegraphs back. Persistent cracks need to be opened up and bridged with mesh tape and multiple coats.
• Demolishing sound plaster to fix a cosmetic problem. Removal is messy, adds disposal and testing costs, and gives up a harder, quieter wall.
• Covering a sagging ceiling without anchoring it. New board has to be screwed into the framing, not just the old plaster. Otherwise the new layer rides on a failing one.
• Ignoring trim depth. When a wall is replaced or thickened, the relationship between the wall surface and the original casing changes. That needs to be planned before work starts, not discovered at the end.
• Skipping the leak. Patching water-damaged plaster before the source is fixed means paying twice.

When to call a pro

A few hairline cracks are a reasonable DIY job. Bring in a professional when a ceiling sags or moves, when cracks keep reopening, when water has softened a section, or when you’re weighing a whole-room skim against replacement and want an honest read on whether the plaster is still attached.

New Line Drywall is a licensed C-9 drywall contractor (CSLB #1051640) based in Castro Valley and working across the Bay Area, including the older housing stock in San Francisco. We handle the drywall side of old-house walls: drywall and ceiling repair, including crack repair and drywall patches set into old plaster, hanging drywall where plaster has been removed, and a skim-coat flat-wall finish over sound plaster. Asbestos abatement, traditional or veneer plastering, and painting are done by other licensed trades; we’ll tell you where their work ends and ours begins.

Call or WhatsApp (415) 756-9502, or request an estimate with a few photos of the wall or ceiling.

Frequently asked questions

Can you put drywall over plaster walls instead of tearing them out?

Often, yes, as long as the plaster is still firmly attached. Thin drywall is screwed through the plaster into the studs or joists, then the joints are taped and finished. Expect the wall to get slightly thicker: outlet and switch boxes usually need extension rings installed by an electrician, and trim may need adjusting. It is not a fix for plaster that is loose, crumbling, or water-damaged.

Can you use regular joint compound on plaster cracks?

Yes, for most cosmetic work. The National Park Service’s guidance on historic plaster lists joint compound as a filler for hairline cracks. For cracks that keep reopening, use a quick-setting compound with fiberglass mesh tape, applied in several coats. Deep voids that go down to the lath need to be built up in layers or filled with patching plaster before finishing.

How do you hang pictures or a TV on plaster without cracking it?

Drill a pilot hole instead of hammering a nail, and put painter’s tape over the spot to reduce chipping. Light frames can go on anchors made for plaster. Heavy items like TVs and shelves should be fastened into a stud, not held by the plaster alone. Old plaster is hard but brittle, and it can crack around fasteners that aren’t well supported.

Will new drywall look different from the plaster in the next room?

It can. Hand-troweled plaster has a very hard surface with slight undulations, and it takes paint differently than drywall. New drywall finished to a basic level may look flatter and show seams under raking light. Where new board meets old plaster in the same room, a higher finish level or a thin coat of compound across both surfaces helps the wall read as one continuous surface.

Sources

1. National Park Service, Preservation Brief 21: Repairing Historic Flat Plaster Walls and Ceilings
2. HomeAdvisor: How Much Does It Cost to Repair Plaster? (2026 data)
3. HomeAdvisor: How Much Does Plastering Walls Cost? (2026 data)
4. HomeAdvisor: How Much Does Drywall Installation Cost? (2025 data)
5. Fixr: Plaster Repair and Removal Cost Guide (updated January 2025)
6. Homewyse: Cost to Repair Wall Plaster (May 2026)
7. U.S. Bureau of Labor Statistics: OEWS, San Francisco-Oakland-Fremont metro area (May 2025)
8. U.S. Bureau of Labor Statistics: OEWS, Drywall and Ceiling Tile Installers, national (May 2025)
9. U.S. EPA: Renovation, Repair and Painting Program for Contractors
10. U.S. Consumer Product Safety Commission: Asbestos in the Home
11. California CSLB: C-22 Asbestos Abatement Classification