Sunday, July 5, 2020

Plaster Repair



Over time the crack in the plaster just behind SWMBO's bed-side table has been getting bigger. Depending on circumstances, I've used various techniques to repair the damage or holes. With the tuckpointing coming on the south elevation, we've had the structural engineer out for a consult on other things. He looked at this and didn't think tearing it off was necessary.

This means that a true repair is still a possibility. 

I've been a member of an evolving list of old house sites on the internet and through them became aware of a product I'm going to try for this repair: Big Wally's Plaster Magic. (Note - no affiliation and no sponsorship...)

In this instance the plaster has cracked and come loose from the underlying lath, especially on the right side of the crack.

And off we go, following the instructions.

I drilled holes through the plaster with a 3/16 masonry bit, making sure to hit the lath. The crack had separated enough that locating the lath wasn't that difficult.

I then vacuumed out all the holes and the crack and squirted the conditioner in every hole.

After waiting the suggested 10 minutes, I used a caulk gun to squirt the adhesive into each hole as directed. The adhesive was runnier than I expected, but no harm resulted. There was just a little more cleanup with a damp rag and bucket of water.

Lastly I used the included screws and washers to clamp down the loose plaster and try to get the right side more-or-less at the same level as the left. And wait for the adhesive to dry/cure.

I waited about 36 hours and then began removing the screws and washers. Everything seemed well-adhered, so it was time to mud and tape.  I'm using fiberglass mesh, rather than paper tape, which should give us better long-term results. I've applied it to some other minor cracks as well.

Now I wait for the first coat to dry. I'm sure it will take two or three coats to get it feathered out so that I'm happy.
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2 comments:

  1. SethJuly 15, 2020 at 10:34 PM

    I'm familiar with plaster washers, but the type that are left in place and skimmed over. I've even seen some people who cut shallow depressions to hide them better (usually just in the soft plaster white coat). This appears to just be an adhesive that bonds the loosened plaster to the lath?

    What kind of plaster compound are you using? Gypsum, lime, or something else?

    I don't have much to repair, but a few random areas. Most of ours is heavy wet-textured too (1920s). That's going to be the toughest part to match.

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  2. MikeAugust 16, 2020 at 10:30 AM

    Yes, this is just an adhesive that bonds the plaster to the lath. The washers are only temporary and act as clamps to hold them together while the adhesive cures. They are far to thick to sim coat over. Be careful when screwing in the washers, you don't want the plaster to touch the lath or all the adhesive gets squeezed out.

    While some people are more particular and try to reproduce old plaster formulas, I've been using "setting-type" drywall compounds for the first coat of my larger repairs (usually 90 rather than 45 - I'm not that fast...). Because it's a bit thicker and cures rather than dries, it's more plaster-like. But then I've just been repairing cracks, not re-plastering larger areas. If I have a larger area or hole, I use a chunk of drywall cut to size and shimmed out so that it's close to level with the surrounding plaster. Then I'm only dealing with the joint. I use "drying-type" ready-mixed compound for the finish coats because it's easier to work with and sand smooth.

    All the repairs I've done have been with a smooth finish, so don't have any experience with how to accomplish textures.

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