How large is this patch that we are talking about? This is the reason that Popcorn ceilings were invented, to hide the imperfections.

As for fixing it, you could with Hot mud, but it can also turn into a disaster, after this disaster.

 

ya do a "prefill" before taping so when the tape goes on it close to flat. or just tape it and skim it. either way would work

 

Or cut a piece of gypsum larger than the patch, cut off some of the backing material and gypsum off the front paper, then use that as your patch. Only works for small holes up to 8 inches, anything larger, you may as well cut back to the studs, add a couple of pieces across the hole, to help secure the patch. Shimming can be done with some ripped wood stock if you have a table saw, or go to some place like Lowe's, Home Depot, and they will either have in stock, or will rip a 2x piece of stock to your spec's for the shims, then just go from there.

I have gone as far as use old wood paint stirrers, run some hot glue along it, attach the patch, then mud, lay the flaps back on the mud, mud over the flaps of the patch, let dry, then sand, apply more mud, let dry, sand, check for any imperfections, lay another coat if needed, then sand, prime, paint.

 

ya do a "prefill" before taping so when the tape goes on it close to flat. or just tape it and skim it. either way would work

OK, great, thanks!

How large is this patch that we are talking about?

4 feet by 2 feet

you could [fix it] with Hot mud, but it can also turn into a disaster, after this disaster.

Greg, is there something about this I should be concerned about or particularly careful about?

 

That is a large patch, so you are talking about the fact, that valleys and high spots will show up more, especially on ceilings. As for using Hot mud, you make as much as you can work with, due to it will set pretty fast if you are slow about applying it. That is why you see professionals use long knifes that can apply a large section of mud at a time, but they also have done this stuff for a long time, so they are able to fix issues if you get someone that knows what they are doing.

You may have to scrape off what you have, pull the patch, and then fix it with another shim, then lay a six foot level across it to check for flush.

 

That is a large patch, so you are talking about the fact, that valleys and high spots will show up more, especially on ceilings. As for using Hot mud, you make as much as you can work with, due to it will set pretty fast if you are slow about applying it. That is why you see professionals use long knifes that can apply a large section of mud at a time, but they also have done this stuff for a long time, so they are able to fix issues if you get someone that knows what they are doing.

You may have to scrape off what you have, pull the patch, and then fix it with another shim, then lay a six foot level across it to check for flush.

Hey Greg, thanks for all the info; I appreciate it. I was taking another look at the patch last night (which has been screwed in but not taped/mudded), and my leaning is to give it a go as is... The uneveness is only in spots and it's literally not much more than 1/16" of an inch at its worst. Does that sound reasonable?

 

i've tried doing the california patch a few times and they never turn out great. i've always had better success just put a backer and putting tape on it and skimming