How to Fix Cracked Plaster: Tips and Guidelines

Cracked plaster and peeling paint from wall — Plaster is both durable and good-looking, but it inevitably develops cracks. Flavio Coelho / Getty Images

Key Takeaways

Fixing cracked plaster involves cleaning the area, filling the crack with spackling compound or joint compound, and smoothing it out with a putty knife.
Once the compound is dry, sand the surface until it's smooth and blend it with the surrounding plaster.
Finally, prime and paint the repaired area to complete the restoration process.

Older homes often have lath-and-plaster walls. Plaster is both a durable and good-looking surface, but there is one drawback: Plaster inevitably develops cracks.

Latex paint will hide hairline cracks in plaster, at least temporarily. The coverup, though, may last only a few hours or a few months. Small plaster cracks have an annoying way of showing up again and again. It may be smarter to enlarge them and fix them properly once and for all.

Making a small flaw bigger may sound like reverse logic, but it's easier to fix big cracks in plaster than small ones. Use plaster of paris, which doesn't shrink as it dries, or purchase premixed plaster repair compound.

What You'll Need

Here are the tools you'll want to have when repairing cracked plaster:

Utility knife
Vacuum cleaner
Plaster of paris or premixed plaster repair compound
Paintbrushes
Scraper or trowel
Wood block
Medium- or fine-grade sandpaper
Primer and paint

Contents

Prepare the Crack
Mix and Apply Plaster
Sand and Let Dry
Sand, Prime and Paint

1. Prepare the Crack

Cut away loose plaster with utility knife. Turn knife to make opening wider and more clean-lined. Remove debris while preserving structural integrity of surface around it. Clean away loose plaster and dust with vacuum cleaner.

2. Mix and Apply Plaster

Mix thick paste of plaster of paris and water, and wet crack thoroughly with paintbrush dipped in water. Pack plaster of paris (or repair compound) into wet crack to its full depth, and smooth surface with scraper or trowel. Let filled crack dry at least 24 hours.

3. Sand and Let Dry

Lightly sand patch when plaster is dry with medium-or fine-grade sandpaper wrapped around wood block. If crack was wide, replaster it at least once more to make surface smooth, rewetting plastered area each time. Let area dry for at least 24 hours after final plastering.

4. Sand, Prime and Paint

Lightly sand patch again, and prime it with thinned coat of paint or primer. When primer is dry, paint entire wall.

Frequently Asked Questions

Can I use plasterboard or drywall to fix cracks?

While plasterboard or drywall can be used for minor repairs, they may not provide the same aesthetic finish as traditional plaster. Additionally, the process for repairing cracks in plasterboard or drywall differs from fixing cracks in plaster, often requiring joint tape and joint compound for a seamless repair.

How do I prevent future cracking in plaster?

To prevent future cracking in plaster, it's essential to address underlying issues like structural movement or moisture problems. Ensure that the building's foundation is stable and properly maintained, and address any water leaks or humidity issues that may affect the plaster. Applying a flexible sealant or caulk around windows, doors and other openings can also help minimize movement and reduce the risk of future cracks forming.

How to Fix Cracked Plaster in 4 Steps