How to patch and repair plaster walls with drywall for the best results

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Patching and repairing plaster walls with drywall and Plaster of Paris can be a daunting task but not impossible. With the right techniques, you can achieve sturdy and perfectly smooth walls. This article explains the steps involved in patching and repairing plaster walls with drywall, as well as useful tips on how to get the best results. 

Almost everyone in construction loves to work with drywall. 

The boards are made with a soft but sturdy material called gypsum and are quicker to install in new homes. Repairs are straightforward and seamless.

But if you have an older home, you might have plaster walls. 

Plaster walls are made with either a wooden framework of thin horizontal boards or a plasterboard and use a metal mesh for corners. Multiple layers of plaster (containing gypsum, lime or concrete) are applied for a thick finish over the wooden frame or plasterboard.

The plaster walls are fireproof, absorb sound well, environmentally-friendly, and sometimes waterproof. 

But this doesn’t change the fact that they can be frustrating to repair.

I’m going to show you how to get around this by using drywall and Plaster of Paris. 

With the right tools and techniques, you won’t be able to tell where the hole was when you’re all done.

bathroom walls after removing tile

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This project started when we decided to renovate our bathroom, ripping out the original tile from the plaster walls. We also had to remove other sections of the wall, leaving holes that needed to be patched with drywall.

In case you’re wondering, the big holes in our plaster walls were where the previous owners tried unsuccessfully to patch the walls with drywall or thinset.

To cut most types of plaster, you can use a drywall knife and a utility knife. You can check out how to patch a hole in drywall to find out how to cut out irregular shapes or work around existing objects.

And here’s a tutorial on the wooden frame removal in case you need it. 

Are you ready to find outhow you can patch plaster walls with drywall? Stay tuned to see how I did it in my house.

Prepping/Shimming the walls

The plaster walls in our house are almost an inch thick. I had to shim out the walls when adding the drywall so it would be level with the other walls. 

Some areas required more shims than others and I know that can make my walls uneven, but it’s better than replacing it entirely.

After shimming out the walls, I was ready to cut the new drywall to fit. 

SIDE NOTE: If you don’t need to patch holes with drywall, you can skip ahead to the part where I talk about patching the walls with a plaster mix.

STEP 1: Cutting out drywall

Normally, when you are cutting drywall, the easiest way is to cut it out in squares or rectangles. 

To cut drywall, score the front of the drywall sheet with a razor (utility knife) and fold the piece backward until it snaps. Then, you are left with the backing paper still attached. Use the razor to cut this paper. 

Not all my drywall cuts were this easy. In some cases, I had to mark the drywall sheet, then fully cut the drywall with the razor or drywall knife.   

cutting out drywall with razor blade

After you cut the drywall, place it into the hole in the wall to make sure everything fits. Trim anything if needed.

patching plaster wall with drywall

And now the fun part began for me: I then had to determine how many shims I would need to make my walls level with the new drywall piece. 

I attached these shims to the 2×4 framing of the wall with nails and then I installed the drywall into place with 1-1/4″ drywall screws. 

If your wall does not have wood to drive a screw into (like a brick wall), you can adhere the drywall to the wall using Liquid Nails. Then, use painter’s tape to hold the piece of drywall in place until it drys. 

SIDE NOTE: It’s a good idea to score the edges of the drywall (so it’s like the rounded edges from the factory) before you plaster.

STEP 2: Prep the walls

After the holes are patched with drywall, clean the walls to prep them for plaster. 

Because my walls previously had tile, I used a scraper to remove all the thinset residue.

scraping wall to remove tile thinset

After that, use a damp cloth or sponge to wipe the walls clean. 

Next, you need to tape the joints of the newly added drywall pieces. I like to use mesh tape to do this. Cut some pieces to fit and save them until you whip up your plaster mix. 

measuring mesh tape for plaster patch job

STEP 3: Mixing the plaster

Now, before we go any further, I want to talk about the issues that I had when I first started mixing Plaster of Paris.

MY MISTAKE:

The first time I used Plaster of Paris, I mixed it with the recommended amount of water according to the instructions.

But I was shocked at how quickly it set.

You had to be able to put something on within minutes or you would have a big mess. 

This makes sense because Plaster of Paris is used for sculpting but I needed more time to work with it. 

THE SOLUTION:

I searched YouTube and I found a wonderful video called How to mix plaster for drywall repairs

I decided to follow this video’s instructions by mixing the Plaster of Paris as normal but then adding in some drywall compound to the mix. 

Adding the drywall compound prevented the plaster mix from hardening too quickly (about 20 minutes of workable time instead of 5). It also gave it the features of the plaster where you can sculpt the mix, so no sanding was needed.

I was SOLD on the thought of not sanding. And guess what, I didn’t sand any, I repeat, ANY walls, and still had smooth walls when I was finished.

Now, this plaster mix will set up a lot faster than the drywall compound, so be ready for that. And you MUST clean everything in between your mixings. You can’t just remix a new batch in the same tub. You have to clean it out completely or the next mix will set up too fast. 

Here is my plaster mixing formula: (I use little kid cups from Ikea) 

  • Two scoops of Plaster of Paris
  • One scoop water
  • Mix those together
  • Add two and a half globs of drywall compound (using a 6” taping knife)
  • And mix everything together again
mixing Plaster of Paris to apply on wall

This was the perfect amount for me to apply the plaster mix to the wall in the time I had before it would start drying. 

STEP 4: Apply the plaster mix to the wall

Do you know how many coats it took me to have smooth walls? It took four coats! 

Hopefully, your walls won’t be as bad. Mine had a lot of deep notches and nicks so it needed more coats. 

You should be able to have smooth walls in two to three coats.

applying plaster mud to wall

The technique to apply the plaster mix to the wall is to use a 12” taping knife (or a smaller one) to apply the mud to the wall. 

Then, use the knife to spread the mud across the wall, making sure to apply a thin, consistent layer.

Applying plaster mix on wall to repair

If you are happy with the coverage of the mud, allow it to set for 10 minutes. 

Then, using the 6” taping knife, lightly smooth out any lines in the mud. Sculpt it!

woman holding taping knife

Also, use a damp sponge and feather out the outside edge so that the new patch will match the wall.

using sponge to smooth walls

Then, allow the mud to dry completely. 

Apply additional coats the same way. 

  • Wipe the mud on and let it dry for ten minutes. 
  • Then, take the taping knife and remove any lines you see. 
  • After, take a damp sponge to feather out the edges.

This technique will give you a smooth finish without having to sand. 

And if you’re curious, here is what our bathroom looks like now. Can you even tell that this wall was patched?!

Overall, plaster walls are great but can be a pain to work with if you don’t know what you’re doing. Hopefully, these tips will help you achieve clean, seamless walls too.

And if your thick plaster walls are slowing down your redecorating plans, here’s how to hang pictures without nails

bathroom wall after repairing with plaster of paris

FULL PROJECT VIDEO:

Are you someone that does better with visuals? Check out the full project video below and don’t forget to subscribe on YouTube so you don’t miss out on future projects!

installing plaster mud on walls with video play icon

So use this tutorial on how to patch and repair plaster walls with drywall so you can have the best results that require no sanding.

bathroom walls after patching and repairing with plaster
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