How To Fill Large Plaster Holes Over Wood Lath

Lesson 4

  How To Fill Large Holes Over Wood Lath  The Right Way

(Avoiding The Common Mistake of trying to fill with joint compound)

If you have an older home in America, your old plaster may have been applied over wood lath.  When plaster comes loose and leaves a hole behind, you can see the lath.

Some people grab some drywall mud and try to fill the recess with that.  NOT a good idea!

A much better way is one I use when doing work for my clients.  Old plaster is usually one quarter to three-eighths inch thick.  And it can often vary in thickness over a short space.  So my rule of thumb would be to get a sheet of quarter-inch drywall and cut a piece that will fill the hole.

You may find that your plaster around the hole is a little thicker than that.  You want the drywall patch you insert to be level with the surrounding plaster.

So how do you get it that way?

My trick involves the use of hot mud. (Remember, we’re talking about quick set joint compound) I put big gobs of hot mud on the back of the drywall piece, press it  gently  into place so it is more or less level all around.  Now give the hot mud time to harden.  Then put in a few drywall screws here and there (through the areas where the hot mud is) and your patch is secure.

Now fill around the edges with more hot mud.  When that is hard, apply drywall paper tape on the perimeter of the patch  and apply two or more topping coats as needed to hide the tape and get the patch blended in.

For a full discussion of how this is done, check out the webpage on plaster wall repair..

http://www.plaster-wall-ceiling-solutions.com/plaster-wall-repair.html

So ... why doesn't it work just to fill the plaster hole with joint compound?

Drywall compound cannot be applied very thick; it shrinks too much.  You would have to apply many successive layers to build up to the thickness of the plaster.  Each layer has to take a day or more to dry before the next layer goes in.  So you see how a simple repair stretches out for days.

A Postscript ------ If you don’t have access to thin (quarter inch) drywall, you could insert a thin
piece of plywood instead.  But you will need to coat the front and back with an oil based wood
primer first, to render it impervious to the moisture in the patching compounds.  Let it dry thoroughly before you insert the plywood.


Alternatively, if the old plaster is three-eighths of an inch thick, just get a piece of drywall of the same thickness and use that to fill in the plaster gap.


Your patching still has more steps. You will have to reinforce where the patch meets the plaster.  So, use the sheetrock if you can get it.  It's a lot faster and less trouble.  Okay?
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Next lesson, we'll learn how to use hot mud in the right way, and avoid common mistakes.

http://www.plaster-wall-ceiling-solutions.com