When you have a joint where neither edge of the drywall is a tapered
edge, do you use joint tape? I always have a problem finishing those
joints off to look good. The combination of the tape and the joint
compound causes a bulge and the always causes me problems.
Yes tape as you would the tapered edges...After it dries go down BOTH sides
with your 12 inch knife/trowl...There will be a ridge of mud in the
center...Don't worry about it and just scrape it off after it dries...Now
coat the butt by going down the center with your 12 inch
knife/trowl....After it dries go down BOTH sides like you did the first time
only this time pull it tight...Think skim coat...Sand it and it should be
I trim back the paper on the adjoining butt edges at a 45, just taking
off about 1/8" of paper, and use paper tape on the joint if I want it
really flat. Cutting back the paper facing leaves a sharper, smoother
edge than the factory or cut butt edge, and it is less likely to
create a bump in the tape. The little recess that is created by
cutting back the paper allows the drying paper tape to be sucked into
the joint a bit, and that allows the followup coats to be thinner.
You'll have to feather out the edges a good bit regardless, but
reducing the height of the high point at the center is a critical
first step in getting it flat.
If you need dead flat, you'll need to skim coat the wall of float the
joint between the studs. The ButtBacker board someone posted works
well for that, but I usually just make my own with a strip of plywood
and a couple of thin pieces of solid cardboard.
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