Are cracks in plaster normal?
Yes, cracks in plaster are common, particularly in older homes and newly plastered rooms. Plaster is hard and fairly brittle, so it shows even small movements in the building. Many cracks are cosmetic, but a few patterns point to something that needs attention. The sections below help you sort one from the other.
Common causes
- Drying and shrinkage. New plaster shrinks as it dries and can develop fine cracks. This is normal within the first months.
- Humidity and temperature changes. Seasonal swings cause materials to expand and contract slightly.
- Settling. New builds and extensions can settle as they adjust, which may crack plaster in places.
- Vibration. Traffic, building work nearby, or slamming doors can contribute in older plaster.
- Moisture. Leaks from the roof, plumbing or windows, or persistent dampness, weaken plaster and make it more likely to crack or fall away.
- Loss of adhesion. Traditional plaster is keyed to wood lath or another backing. When that bond fails, plaster can sag away from the wall and crack.
- Openings and alterations. Replacement windows, removed walls, or new loads can shift stress to corners and around doors and windows.
Types of plaster cracks
- Hairline and spider cracks. Fine, random or web-like lines. Usually cosmetic.
- Straight cracks along joints. Often where boards or materials meet.
- Corner and ceiling-line cracks. Common where walls meet ceilings or each other, because the junction moves more.
- Cracks around doors and windows. Stress concentrates at corners of openings. Diagonal cracks from corners deserve a closer look.
- Diagonal or stair-step cracks. Can indicate differential settlement, especially if wide or growing.
- Map or craze cracking. Fine networks that suggest surface drying or an incompatible coating.
How to tell if a plaster crack is structural
A structural cause becomes more likely when cracks:
- are wider than about 1/4 inch or visibly growing,
- run diagonally from door or window corners, or are wider at one end,
- appear with sticking doors and windows or sloping floors,
- appear on multiple walls or floors in a pattern,
- come back soon after repair.
For a broader checklist and how to monitor a crack, see our guide to interior wall cracks. For diagonal patterns in masonry, see diagonal cracks in a brick wall.
Loose, hollow or bulging plaster
Tap the wall gently with your knuckles. A hollow, drummy sound near a crack can mean the plaster has separated from its backing. Plaster that is loose or bulging may need to be re-secured or replaced by a plasterer. On ceilings, treat sagging or loose plaster as a safety issue, as pieces can fall; see ceiling cracks and structural damage. Keep people out from under any ceiling that looks like it is sagging.
Safety before you repair old plaster
Older homes can contain hazardous materials. Paint in homes built before the late 1970s (in the US) may contain lead, and some older plasters, textured coatings and joint compounds contain asbestos. If you are unsure and plan to sand, scrape or cut into old finishes, have a sample tested first, and use a qualified professional if hazardous material is confirmed. See asbestos in drywall mud for how sampling and testing work. Avoid dry sanding of old paint and plaster. If testing is not done, treat the material with caution and ask for professional advice rather than creating dust.
How to repair a minor plaster crack
For a thin, stable crack in sound plaster, a typical approach is:
- Wear eye protection and a dust mask suitable for fine dust, and confirm the material is safe to disturb (see above).
- Scrape the crack with a utility knife or similar to form a slight V-groove and remove loose material.
- Brush and vacuum the dust, then lightly dampen the edges or use a suitable bonding primer so the old plaster does not draw moisture out of the filler too fast.
- Press a patching or setting-type filler into the crack with a putty knife. Use mesh or paper tape over wider cracks.
- Let it dry, apply a thin finishing coat, feather the edges, and sand lightly.
- Prime and paint.
Follow the product’s directions for drying time. Wider or deeper cracks, or cracks where the plaster feels loose, usually need more than filler.
When cracks keep coming back
If a repaired crack reopens, something is probably still moving. Possibilities include seasonal movement at a corner, a failing bond to the lath, or ongoing settlement. Using a more flexible filler at joints that move can help, but repeated cracking in the same place is a reason to investigate instead of repainting. Check for water sources too, as damp plaster will keep failing until the leak is fixed. If a plumbing leak is possible, see the signs of a leaking pipe.
Does home insurance cover cracks in plaster?
It varies by policy and cause. Many policies exclude gradual wear and settling, while sudden damage such as a burst pipe may be handled differently. Some policies include specific cover for subsidence or ground movement. Check your wording and contact your insurer before repairs, and keep dated photographs.
FAQ
When should I worry about cracks in a plaster wall?
When they are wide, growing, diagonal from openings, or paired with sticking doors, sloping floors, damp or plaster that is loose or bulging.
My wall plaster has cracks. Is this normal?
Fine cracks are common, especially in new plaster or older houses. Monitor them and repair them if they are stable.
How can you tell if a plaster crack is structural?
Look at width, direction, growth and companion symptoms. If several indicators are present, ask a structural engineer to inspect.