Plaster Wall Repair Challenge: Fixing Holes

Plaster wall repair becomes a necessity when you are faced with multiple holes in your plaster. Damage from rambunctious children, moving furniture, holes cut to reach wiring or plumbing - all confront the homeowner over time. Many folks shudder at the prospect of repairing plaster walls (or repairing plaster ceilings). They may not have a clue of what to do.

But it need not be the end of the world. With some tips, simple tools and materials, repairing holes in plaster walls can be mastered. How you go about it depends on the size of the holes and what is - or is not - behind them.

Much old plaster has wood lath backing. When chunks are missing, you can often see the wood strips behind. If this is the case, your plaster wall repair can be fairly simple, depending on the size of the hole.

Plaster Hole With Lath Showing

1. The lath shows.

Okay, here your backing is still in place. Now you just have to replace the missing plaster with new material. If the hole is not big, say two inches or less, you can fill it with two or three successive layers of hot mud or plaster of paris. The second stuff you can buy in smaller boxes. If you need to repair lots of holes in your plaster walls, it would pay you to go ahead and buy a bag of hot mud (chemically setting joint compound). Get a slower setting time, like 60 or 90 minute.

What about big holes in plaster?

How I do it. If the lath is showing behind, I cut a piece of thin sheetrock, usually three-eighths or one-quarter inch thick, and fit it into the hole with glue on the backside (Liquid Nails, or dollops of hot mud) and drywall screws through the lath. The point here is to fill the hole and do so with the new material as close to level with the surrounding plaster surface as I can get it. I use hot mud to fill any gaps around the edges. Then I apply drywall paper tape over the drywall-plaster perimeter all around the edge. When that is hard, I put at least two topping coats over the tape, more if necessary.

Wherever the filled gap around the edges is wider, say a half inch or more, lay the tape in short strips (3 inches or so) across the edges instead of lengthways. Side by side, without overlapping. This provide plenty of reinforcement. Then do the topping coats as usual. Plaster wall repair done right!

Tip: Since plaster over wood lath often varies an eighth inch or more in actual thickness, it can be tricky to get the drywall patch level at all points with the surrounding surface. A handy way I have found to deal with this: Use the thinner one-quarter inch thick sheetrock. Before laying the patch into the hole, put big dollops of hot mud on the back around its edges as well as several at random in the middle. Now press it GENTLY into place. The moment it is fairly level, stop!

Now give it an hour or more for the hot mud to set up. Once that happens, your "liquid shim" material has given you a solid backing and a more or less correct level at all points. Put in a few drywall screws here and there and you are ready to tape the edges.

Marking on the front of your sheetrock patch where your hot mud dollops will be (on the back) before you place the patch in the hole will show you where to put in the screw later. You want to avoid having an air space directly under where you put in the screw. If there is a space, you will likely over sink the screw head and get a poor attachment.

2. No backing in the hole. Now it gets a little more complicated. To do plaster wall repair of this kind, you have to put in your own backing. If the joists or studs are showing on two sides of the hole, you can scab on a wood strip on each side and screw your patch to that.

If no framing is showing, you can attach one-by-two or one-by-four wood strips on opposite sides of the hole. Cut the strips to length, making them several inches longer than the width or length of the hole. Place the first inside the hole and press it tight against the back the plaster lath. With the other hand, take a long drywall screw and with a screwgun, screw through the plaster and lath above the hole and into the wood strip you are holding. Do the same at the bottom of the hole. Then repeat with the second strip on the opposite side of the hole.

Tip: With a wood lath system, you will find that when the plaster was originally applied, it squished through the gaps between the laths and mounded up on the back of the laths. As you try to press your wood backing up against the back of the laths, you may discover that it is hard to get it to lay flat. In that case, you will have to reach carefully behind and break off some of those lumps so that your wood strip can lay flat against the lath.

Break off no more than is necessary of the plaster on the back of the laths. These humps are the keys that hold the plaster face securely in place. I usually compensate for these localized weak areas by adding extra tape over the face when I later tape the sheetrock-plaster juncture around the patch perimeter.

You don't have to use wood to back these hole patches. Five inch wide drywall strips can be glued to the back of the laths. Use big dollops (there's that word again!) of hot mud, and leave ample edges protruding into the hole to provide backing for the patch. When the backing "glue" is hard, cut your sheetrock piece to fit the hole and put big gobs of hot mud on the back side where it will rest on the backing. Press the patch gently into place until it is level, then stop. Let set up, tape, etc.

3. Holes in rock lath and plaster. Simpler to deal with than wood lath plaster. With this kind of hole, and no backing showing, glue in drywall strips as just described and fit the patch in. It's always a good idea first to reach behind the hole and wipe away any debris on the back of the lath, so you can get a good bond when you glue the backing in place.

Plaster wall repair (and ceiling repair) gets pretty simple when you have done it a few times. Who knows? You might become your neighborhood plaster repair expert!

Note: Have you repaired a number of holes (and cracks?) and now want to get rid of the rest of the old texture? Your solution is

to skim coat the plaster

P.S. A few final thoughts: Since you want your plaster wall repair to look good, you may find it necessary to apply more than just two coats over the taped perimeter. If it happens that your patch is a little recessed, you will need to level the patch to match the surrounding plaster. So don't be afraid to apply as many topping coats as you need to for things to be flat.

When the holes are all patched, you may need to match the surrounding textures. Here are some good tips to help you. Go here to learn how to do ceiling or wall textures.

Once you have finished your texture work, don't forget the last step in your project - apply your drywall primer. Some useful tips.

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