Here are some techniques to use if you have damaged plaster and lath walls, such as holes caused by electrical work. You’ll first repair the lath, and then patch the hole.
How to Repair a Hole in Lath and Plaster?
It’s crucial to use the correct materials and techniques for lath and plaster repairs in Auckland. Use a lime-based, softer plaster that sets slower. This plaster was developed for their plaster repair products. It takes an hour to dry, doesn’t crack or delaminate, and requires no sanding. Avoid the so-called “patching plaster” sold in home centers. It is much harder than original wall plaster and sets within seconds.
When the lath in your ceiling is still intact and you have holes to fill, it is easy to patch them by troweling on mud. In the 20th century, plaster was used over wooden lath that were spaced about half an inch apart. The first coat was applied to the gaps between the laths, creating a stable foundation. The base coat was applied after it had dried. The blue board is a type of wall board that’s made to be plastered. However, troweling the base coat on is quicker.
How to Repair Plaster and Lath in Six Steps
1. Repair the Lath
Refasten any loose lath pieces and replace any missing lengths. Always drill pilot holes and use drywall screws to avoid splitting wood. If you don’t have a stud for the lath ends, slide a piece into the gap and screw it parallel to the studs. You can then screw in new or loose lath as if the stud were there.
2. Stabilize the wall’s edge
Drill holes around the damaged area every 3 inches, approximately 1 inch away from the edge, using a 3/16″ masonry bit. Drill the hole until the bit hits lath. If the bit misses, make a pencil mark next to that hole. Vacuum out the holes, then spray with plaster conditioner. Wait 15 minutes and then spray plaster adhesive into all holes that are not marked. Remove any excess plaster adhesive with a damp cloth.
3. Wet the Substrate
The exposed edge of the plaster and dry lath will absorb water from wet plaster, before it can harden. To avoid this, you can saturate the surfaces with conditioner. To remove any overspray or drips, use a damp cloth. Wait for the conditioner to dry, about 20 minutes before moving on to next step.
4. Scratch Coat
Mix Plaster magic patching paste in a bucket of cool tap water until it reaches the consistency and color of peanut butter. Use a margin trowel to spread the mixture over the lath and along the edge of the old plaster. This layer should be half as thick as the original plaster. Scratch the patch with a scarified and then scrape off any blobs.
5. Trowel on Second Coat
Wait for the scratch coat to be firm, about an hour. Then mix a new batch to a slightly thin consistency. It should resemble buttercream frosting. Then, using a trowel, smooth out the mixture flush against the wall surface. Scrape off any excess. Wait an hour more for the coat to dry.
6. Smooth the Top Coat
Use a 6-inch tapering knife to smooth out the patch. Cover the patch with an even thin layer of joint compound. Allow to dry overnight. Apply a second layer and gently scrape the surface to make it smooth. Spread another coat on the third day. After it has dried, use a damp sponge to smooth it. Now the patch is ready for priming and painting.
How to Patch Plaster Walls if the Lath is in Good Condition
If the lath is still sound behind the old wall plaster, you can patch it by troweling on mud.
How to Repair Holes in Plaster in Seven Steps
- Use a flat trowel and force base coat into lath. After removing all loose plaster, coat exposed laths with plaster basecoat, making sure to get the material in the gaps between laths. Plaster that is used between the laths, also known as “keys”, locks the material into place. Mix the plaster with a stiff mixture to prevent it from sagging before it sets. The base coat is strengthened by adding nylon fibers to the mix.
- Use the flat trowel and fill in the area. After the base coat has been nailed to the lath with the key, you can add more basecoat. When the base coat has been rolled to the same level as the old plaster surface, use the trowel and smooth the area well. This will reduce the need to sand.
- Paint on the bonding agent. Once the base coat has dried, apply a plaster adhesive to the old plaster and over the top. The bonding agent is a water-based adhesive that ensures a good adhesion of the old and new work.
- Tape joints. Use nylon mesh tape to cover the joint between the base coat and old plaster. This will help to reduce the chance that any cracks in the base layer will show up on the final surface.
- Use a tapeing knife to apply a thin coat of setting-type veneer over the mesh tape. Setting plaster dries quickly and allows for quick progress.
- Finish the patch with two coats of joint compound. Finish the patch by applying two coats of Joint Compound. Allow the first coat to dry and then smooth on the second. It is important to create a large area that can be blended into the existing wall, without creating an obvious high spot.
- Sand the surface. Blend the new plaster with 220 grit paper after the second coat has dried. First, focus on blending in the edges of the patch to the wall. Then smooth the center.
You can see that the process of patching up missing plaster is similar to the original installation. The base coat, followed by a few finish coats and some sanding will make the old walls look brand new.