Thick joint compound to level with plaster - can this be rescued?

Question

We recently completed a home rewire that went well! The team was minimally invasive but did have to trench some areas near block wall with no access. They've sent their drywall repairperson out to close up the walls, and I'm concerned about the approach they're using:

For context: our house is from 1964 and has plaster-over-gyprock walls that are just shy of an inch thick in most places. For the pictured repair, the contractor screwed 1/2" sheetrock directly to the furring strips, then filled in the trench level with the plaster using USG "Ultra Lightweight" premix. This has, unsurpringly, cracked really badly. It's been well over 48 hours and this is still soft & easily dented as well.

I know this is not the final layer, but we've been told that the contractor will be out tomorrow to wrap up. I'm worried about adding a skim layer over this hunk of PlayDoh before it's fully cured, as it feels like anything put on top of this mess will also crack or be otherwise seriously at risk of some sort of cosmetic failure. Even once it's fully cured (in what, a week or so?), this feels problematic.

So, my ask: is cracked joint compound a low-risk base layer, or is this opening us up to cosmetic problems in the near future? I don't want to overreact to an ugly-but-acceptable approach, but there's a lot more patching needed around the house and I'm worried about allowing this project to go further if we're going to have to cut it out and restart it all in a couple months.

Answer 1

Ugh. You patch plaster with plaster, or at least use hot mud (setting compound.) I would question the qualifications of the contractor.

On the other hand, I built cove corners (on drywall walls) with premix years ago that cracked badly for the first coat, but have been fine (those did, however, get throughly dried/cured before being re-coated.) Took about 3 coats to get them solid, as far as I recall. It was something of a impromptu experiment on a small room, so I didn't bother to go buy a bag of setting compound to do it; And I was only working for me...

Answer 2

There are several types or categories of drywall compound. Each has its strengths and weaknesses; these make the types more- or less-suited for various site conditions. (Is the site humid, is it cold, what's the allowed timeframe, etc.) A skilled person can make any of the muds work well enough almost anywhere -- but a skilled person also would choose a mud type that makes his job as easy as possible while still producing an acceptable end product. Your drywall person didn't do that very well.

In my "advanced amateur" (non-professional) opinion, it's not a good move to use all-purpose mud for filling a trench 3/8" deep and 4 inches wide. Filling that with setting-type mud is a "solid maybe" because this kind hardens by chemical reaction, like concrete, rather than by drying. It does still take a very long time to dry when piled up that deep though. Though the setting type shrinks and cracks much less than the all-purpose does, I expect it'll still shrink noticeably if used to fill a void this large.

I suspect that the approach your drywaller took probably can be made to work. The cracks that are visible now probably will get partially filled by a subsequent coat, and that'll help prevent chunks of mud from wobbling and falling out. It's going to take more effort (return visits) to finish well, though, and it's going to take many days to dry completely. You'll probably be well-advised to let it sit open for a while before painting because primer and paint will impede the drying of the joint.

What I would have done is the following:

Since the opening is "just shy of an inch" deep in most places we need most of an inch of filler. The half-inch drywall was a good start but 5/8" drywall might have been better. Or a half-inch paired with a piece of 1/4" or 3/8" drywall. Or two layers of 3/8". Or install just the right amount of shim stock first, followed by a single layer of 1/2" drywall. Whatever the stackup is, once it's within 1/8" (but hopefully closer, like 1/16") of the existing surface, fill a little more with mud, then proceed to tape like normal.