Many older homes may still have some walls and ceilings made of plaster and lath instead of the now standard drywall or wallboard. If you have holes or cracks in your plaster walls or ceilings, repairing them isn’t difficult. It can, however, require a bit more extra time and skill than patching a hole in drywall. Keep reading to learn how.
How to Fix Cracks in Plaster
Step 1: Prepare the Room
Before starting, cover the floor with plastic drop cloths and fasten the cloths in place using painter’s tape. This will protect the floor from any spilled or splattered plaster or joint compound and make clean up a bit easier, as much of the dust from sanding will collect on the drop cloths. Close off the room using plastic sheeting and painter’s tape and cover vents to keep sanding dust from travelling through your HVAC system.
Helpful Tip
A shop vacuum is a great tool for cleaning up sanding dust.
Step 2: Smooth and Patch
Smooth and remove loose plaster pieces and any jagged edges on the surface around the crack with a putty knife. Use a cloth or rag to wipe away dust and debris. Dampen the area with a spray bottle and water. Follow the manufacturer’s instructions to mix dry plaster with water in a large bucket. Pour the plaster from the bucket into a mud pan. Apply a layer of plaster to the crack with a 4” wallboard knife, making sure the layer is even with the rest of the wall. Crack repairs usually need only one layer of plaster. Allow the area to dry for 24 hours.
Safety Alert!
When plastering, wear safety goggles, a long sleeve shirt and cotton work gloves for eye and skin protection. Wear a sanding respirator to prevent inhalation while breaking dried plaster or when mixing.
Helpful Tips
Excess moisture in the wall or room can affect the plastering, so make sure to fix any leaks or causes of moisture several weeks before plastering.
The best temperature for plastering is between 55 degrees and 70 degrees. Keep the room at this temperature at least 24 hours before plastering to ensure the walls are completely dry. The room must stay at this temperature during plastering and until the plaster has completely set.
You can also use spackle and a joint compound to patch cracks. For the smallest cracks, you can use spackle. Apply small amounts with a 2” putty knife until the crack is covered. Let the spackle dry for the amount of time specified by the manufacturer. Sand it smooth. For larger cracks, you can use a joint compound. First, apply a strip of self-adhesive fiberglass wallboard tape across the entire length of the crack. This will help keep the crack from growing. Apply the joint compound with a 4” wallboard knife over the tape until it is completely covered. Feather your coverage about 3” all around the taped area so that it will blend in with the rest of the wall. Allow it to dry and then sand it smooth with fine-grit sandpaper. Apply a second coat of joint compound and feather this layer out 6” to 12” from the repaired area to help it blend in further. Allow it to dry again before proceeding.
Safety Alert!
Wear safety goggles and a dust mask or respirator if you will be sanding a large repair area.
Step 3: Sand, Prime and Paint
Using a piece of fine-grit sandpaper, sand the patched area until it is smooth. Wipe away sanding dust and debris with a damp cloth. Wipe the patch down with a damp sponge and paint the area with True Value EasyCare Ultra Premium Interior Primer/Sealer and let it dry completely before continuing with your paint base coat.
How to Repair Holes in Plaster
Step 1: Remove Damaged Plaster
Remove the damaged plaster by using a cold chisel and a ball peen hammer to chip the damaged plaster off the wall. Be sure not to chip too hard or you will damage the lath, which is the wood structure that supports the plaster. Using a utility knife, smooth the inside edges of the hole.
Step 2: Apply Latex Bonding Agent
To make sure the dry plaster and lath do not absorb too much moisture, use a paint brush to apply a latex bonding agent to the lath and exposed plaster. Ask someone at your local True Value hardware store for the right bonding agent for the plaster.
Step 3: Apply and Cross-Scratch Plaster
Fill in the hole with plaster using a 10” wallboard knife. To help the second coat stick well, cross-scratch the first coat of plaster as it begins to set. This scratching or scoring with a putty knife or similar bladed tool creates shallow grooves (either vertically or horizontally) in the first coat that helps create a secure bond when the second coat is applied.
Step 4: Apply Second Layer
After letting the first coat dry for 24 hours, use a spray bottle to dampen the area with water. Distribute a 3/8-inch thick layer of plaster over the hole and cross scratch as before. This layer must also dry for 24 hours.
Step 5: Apply layer of Joint Compound
Apply the joint compound with a 10” wallboard knife after the second layer is dry. As you would with a wall crack, feather coverage about 3” around the repair area so it will blend in with the rest of the wall. Let it dry and then sand it smooth with fine-grit sandpaper. Apply a second coat of joint compound and feather this layer out 6” to 12” from the repaired area to help it blend in further. This final layer must be applied very thin to blend with the wall and must dry for 24 hours. Once completely dry, wipe the area with a damp sponge and sand until it is smooth with fine-grit sandpaper. Now you can prime and paint.
How to Repair a Lath
In some cases, you may need to repair the wood lath behind a hole. If so, follow the steps below.
Step 1: Insert Metal Lath in the Hole
If the lath behind the hole is damaged, cut the damaged wood out with a keyhole saw or similar cutting tool, or with a chisel and mallet. Take a piece of metal lath, which is similar to heavy screen, and insert a wire loop at the center of the lath. Holding the wire tightly, push the metal lath into the hole and pull the wire so that the metal lath is pressed firmly against the inside of the hole.
Step 2: Apply Plaster Over Lath
Twist the metal wire tightly around a wooden dowel making sure the dowel is pressed firmly against the wall. Apply a coat of plaster until it fills the hole and cross-scratch it as it begins to set.
Step 3: Distribute Joint Compound
Once the area is dry, remove the wooden dowel and cut the wire with wire cutters. Apply a thin layer of joint compound and let it dry for 24 hours. The area can be painted or wallpapered after sanding and being wiped down with a damp sponge.
Congratulations! You’ve just repaired your plaster walls.
Fix Cracks: Project Shopping List
Here’s what you’ll need to complete this project successfully.
- Plastic drop cloths
- Painter’s tape
- Plastic sheet
- Shop vacuum
- Putty knife
- Cloth
- Rag
- Spray bottle
- Dry plaster
- Large bucket
- Mud pan
- 4″ wallboard knife
- Safety goggles
- Long-sleeved shirt
- Cotton work gloves
- Sanding respirator
- Spackle
- Joint compound
- Putty knife
- Self-adhesive fiberglass wallboard tape
- Fine-grit sandpaper
- Sponge
- EasyCare Ultra Premium Interior Primer/Sealer
- EasyCare Ultra Premium Interior Paint
Repair Holes: Project Shopping List
Here’s what you’ll need to complete this project successfully.
- Cold chisel
- Ball pein hammer
- Utility knife
- Paintbrush
- Latex bonding agent
- 10″ wallboard knife
- Spray bottle
- Joint compound
- Fine-grit sandpaper
- Sponge
Repair Lath: Project Shopping List
Here’s what you’ll need to complete this project successfully.