what I need to know is this: how big a gap will that pre-mixed "mud" fill? maybe 1/4 in. ? what about bigger gaps? say 1/2 in.? isn't there some filler you can use for big gaps? I've got a strip about 3/4 in. wide that I'd liike to fill rather than cut a strip of sheetrock to fill it.
1.) Filled with a narrow cut of sheetrock, then taped and coated.
2.) You can sometimes get away with filling the gap with compound several coats (allowed to dry), then applying tape over the area, then coating like a seam.
In your 3/4" situation, I suggest that your install a narrow sliver of sheetrock, then apply compound over it, then apply your tape, coat, etc...
Drywall mud tends to shrink as it dries, which is why it is not a good idea to fill cracks with it. I would say the number 1 failure I see in DIY projects has to do with drywall. If you take your time, and bed and tape the joint after installing a filler strip, then go back and skim coat over it, you will be much happier with the result. One last thing: Don't try to make it happen all at once.....you have to give the mud time to set between coats...the difference in good looking job or something you hope no one ever sees.
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