The drywall may be up, but the job isn't done yet. Now it's time to turn all those pieces of drywall into one solid wall ready for priming and painting. The long edge of each drywall sheet is beveled – purposely made thinner than the rest of the sheet. This creates a trough when the edges are put together. Seams of butt joints with beveled edges get a strip of paper reinforcing tape and three coats of joint compound. Each coat is slightly wider than the previous coat, and the final coat is 24 inches wide.
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Fill the troughs along the sheet edges.
Build up about an inch of joint compound on a 6-inch knife, and fill the trough with compound.
Put tape in the trough.
Put paper drywall tape in the compound in the trough, pushing it in every foot or so to hold it in place.
Pull the knife along tape.
Pull the knife along the tape, embedding it in the mud. If you start in the corner and work toward the middle of the room, the tape will pull loose. Start in the middle and work towards the corners, at least until you have the ends embedded in the compound.
Apply a second coat.
Let the compound dry overnight and apply a second coat of compound with a 10-inch knife. Let it dry overnight.
Apply a third coat.
Thin the joint compound with water to the consistency of mayonnaise before you apply the third coat. The thinner compound goes on more easily, fills irregularities, and is less likely to leave small pinholes as you spread it. Apply the compound with a 12-inch knife.
No coat of joint compound goes on perfectly. Let the third coat dry overnight, and sand the surface smooth using a pole sander and 120-grit paper. Start by folding the paper around the ends of the pads and tightening the wing nuts on the back to clamp it in place. Run the pole over the joints until you get a smooth surface with no steps between the edge of the compound and the drywall, and with no ridges or pinholes elsewhere in the compound.
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