Why Is My Plaster Patch Not Blending Well? 8 Tips to Fix It

Ah, the fun of older homes. Whether yours is still a diamond in the rough or you’re just polishing up a restored gem, chances are you’ll need to repair your plaster walls sooner or later. If your plaster patch is not blending properly, these eight tips will help you get a smooth, seamless finish.

1. Reinforce the Lath

Plaster is a wall material that was popular in the U.S. until the 1940s. Unlike drywall, which is the popular option today, plaster walls and ceilings were made by troweling a thick paste onto a framework of small wooden sticks called lath. 

If your plaster patch isn’t blending, it could be because the plaster behind your patch has come loose from the lath, or the lath has come loose from the studs. That could cause your plaster to crack or prevent the patch from sitting flush with the rest of the wall. 

Make sure all lath is tight and secure. If the wall gives when you press on it, that’s an indication your patch won’t blend well. You may need to add another piece of lath behind your patch. Use screws with plaster washes to secure it.

2. Get the Right Consistency

Make sure the plaster you’re using for your wall repair is the right consistency—not too wet or too dry. Either one could mean your patch won’t adhere tightly to the wall underneath. It should be the consistency of peanut butter (or pudding, depending on the type of plaster). Review the package instructions to make sure you’ve got the right ratio of water to powder.  

3. Keep Your Working Area Moist

Troweling wet plaster onto a dry surface could also affect your patch, as the moisture in the plaster could absorb into the wall. When plastering a wall or ceiling, keep a small spray bottle of water handy and use it to moisten your working surface before you add the plaster.

4. Use More Coats

A common misstep when plastering a ceiling or covering holes in your wall is to use too few coats. Rarely will you be done after one coat (although that would certainly make the job go faster!). Instead, you’ll need to use three or even four coats to ensure a smooth finish. Plan on working in steps, and don’t forget to account for drying time. 

5. Let the Plaster Dry Longer

If you don’t let the plaster dry (or cure) completely, your next application might pull off pieces of half-dry plaster, leaving the surface pitted and patchy instead of smooth. Follow the package directions closely, and give yourself extra hours, or even overnight, especially on rainy or humid days. You’ll get a much better result, even if it takes a little longer to get the job done.

6. Be Firm With Your Trowel

You might feel like a light touch will lead to a better-blending patch, but the opposite is true. You’ll need to trowel the plaster firmly onto the surface to keep your patch flush with the wall. Use a small putty knife to press and scrape the wet edges of your plaster patch to blend with the wall. 

And don’t try to get each coat perfectly smooth with the trowel when wet. Instead, you can let the patch dry with a rough surface, and then use the trowel to scrape down the high points after it has fully dried. Dried plaster is very tough, so you can use a little force if it’s bumpy. Just be careful to hold the trowel almost flat so you don’t gouge the surface.

7. Finish With Joint Compound

If you’re looking for a very smooth type of plaster finish, use joint compound as your final coat. Make the layer very, very thin, like a skim coat. If you can see the wall underneath, all the better. Make sure the joint compound is the right consistency and allow it to dry completely. You may not even need to sand. Use a damp cloth or sponge to remove any remaining dust from the surface of your plaster patch and make sure it’s dry before moving on.

8. Prime Before Painting

If you don’t prime before you paint over the plaster patch, it will soak up topcoat and look very different from the rest of the surface. Apply at least one coat of heavy-duty primer to prepare the patch for painting, ensuring the wall appears smooth and uniform.

While getting a good blend between a patch and the wall is possible when you go slowly and take your time, you might prefer to call a plaster repair pro near you. They have the skills and experience to make even big bumpy patch jobs look seamless.