Patching plaster walls is a valuable skill if you have an older home and want to preserve its integrity and appearance. While it may seem daunting, you can effectively repair damaged plaster with the right tools and techniques. In the video above, This Old House general contractor Tom Silva shows the best techniques for patching plaster.
Assessing the Damage
Before beginning any repair work, assess your plaster wall damage to determine the correct repair method and materials.
Identify Type of Plaster Damage
Plaster walls can suffer from various types of damage, including:
- Cracks
- Holes
- Loose or bulging sections
- Water damage
Determine the Depth of Damage
To accurately determine the depth of the damage, probe the affected area with a utility knife. By inserting the knife into the plaster, you can feel where it hits the lath beneath, giving you an idea of the plaster’s thickness. You’ll need this information to choose the appropriate repair materials.
Measure the Damaged Area
Once you’ve identified the type and depth of damage, measure the affected area. This will determine the patch size you need and the amount of materials required for the repair.
Tools and Materials To Patch Plaster
Here’s a comprehensive list of items you’ll need:
- Adhesive-backed nylon joint tape
- Drill/driver
- Drywall hawk
- Drywall knife
- Drywall patch
- Dust mask
- Joint compound
- Painter’s 5-in-1 tool
- Primer and paint
- Safety goggles
- Sandpaper (150-grit and 300-grit)
- Tape measure
- Utility knife
Using the correct tools not only makes the job easier but also creates a professional-quality finish.
Preparing the Damaged Plaster
Good preparation is key for a smooth and long-lasting repair. Follow these steps to prep the damaged area:
- Score the plaster: Using a utility knife, score around the damaged area to create a clean edge for the patch.
- Remove loose plaster: Carefully pry off any loose or damaged plaster using a painter’s 5-in-1 tool or putty knife.
- Clean the area: Remove all debris and dust from the damaged area so there’s strong patch adhesion. Make the surface as smooth as possible.
Cutting and Fitting the Drywall Patch
Selecting the right patch material is important for a successful repair. In the video, Silva recommends using a 3/8-inch thick drywall patch, as this typically matches the thickness of traditional plaster walls.
Measure and Cutting the Patch
- Measure the damaged area, adding a slight overlap for full coverage.
- Cut the drywall patch to size using a utility knife or drywall saw.
- Test-fit the patch to make sure it covers the damaged area completely.
Be sure the patch fits snugly into the scored area to maintain the wall’s structural integrity.
Secure the Patch
- Hold the drywall patch against the wall and mark its outline with a utility knife.
- Score the plaster along the marked outline to create a clean edge.
- Set the drywall patch against the wall and secure it with 1 1/4-inch drywall screws.
- Make sure the patch is firmly in place without any gaps.
Applying Joint Tape and Compound
With the patch securely in place, it’s time to blend it in with the surrounding wall.
Tape the Seams
- Cover the seams around the patch with adhesive-backed nylon joint tape.
- Press the tape firmly for good adhesion and remove any air bubbles.
- Make sure the tape is smooth and covers all edges.
Taping the seams correctly prevents future cracking and creates a smooth finish.
Apply the First Coat of Joint Compound
- Using a drywall knife, apply a coat of joint compound over the taped seams and screw heads.
- Clean the knife off thoroughly.
- Press the knife horizontally against the wall at the bottom, apply a bit of pressure, and then gently glide it upwards to remove excess compound and flatten out the surface. This is called feathering.
- Feather all areas as you go.
- Allow the first coat to dry completely, typically 24 hours.
Sanding and Applying Additional Coats
To achieve a seamless finish, you’ll need to apply multiple coats of joint compound and sand between each application.
Sand the First Coat
- Once the first coat is dry, sand it lightly with 150-grit sandpaper.
- Remove all dust with a clean, dry cloth or vacuum.
- Check that the surface is smooth before applying the next coat.
Apply Subsequent Coats
- Apply a second, slightly wider coat of joint compound to the seams.
- Allow the second coat to dry completely.
- Sand with 150-grit sandpaper and remove dust.
- Apply a third, even wider coat of joint compound.
- Allow the final coat to dry completely.
- Feather each coat to blend into the surrounding wall.
- Once the final coat is dry, sand the entire patched area with 320-grit sandpaper to achieve a smooth, even surface that blends perfectly with the surrounding wall.
Priming and Painting
The final step in the plaster patching process is to prime and paint the repaired area to match the rest of the wall.
Prime the Patched Area
- Apply a coat of primer to the patched area and surrounding wall.
- Allow the primer to dry completely according to the manufacturer’s instructions.
- Be careful to make sure the primer is evenly applied.
Paint the Wall
- Choose a paint color that matches the existing wall.
- Apply two coats of paint to the patched area and surrounding wall, allowing each coat to dry completely between applications.
- Use a quality paintbrush or roller for a smooth finish.