Inside corners are a natural place for hairline cracks to
appear. This can be prevented by first applying a thin
layer of wallboard compound, followed immediately by
strips of paper or fiberglass wallboard tape pressed into
the damp compound. You will want to use fiberglass tape if
you use a quick-setting compound and paper wallboard tape
if you use a regular premixed wallboard compound.
Use a 4-inch wallboard knife to apply a thin layer of
premixed wallboard compound to both sides of the inside
corner.
Fold a strip of paper wallboard tape in half, creating a
crease by pulling the strip between your thumb and
forefinger. Then position the end of the folded tape strip
at the top of the corner joint. Press the tape into the
wet compound first down one side of the corner joint, then
the other, carefully checking to make certain the creased
portion of the tape aligns with the corner of the joint.
Then smooth both sides of the corner.
Apply a second coat of wallboard compound with a corner
trowel. After the second coat dries, apply a final coat of
compound and smooth it with a wet sander.
Use a 4-inch wallboard knife to apply a thin layer of
premixed wallboard compound to both sides of the inside
corner.
Fold a strip of paper wallboard tape in half, creating a
crease by pulling the strip between your thumb and
forefinger. Then position the end of the folded tape strip
at the top of the corner joint. Press the tape into the
wet compound first down one side of the corner joint, then
the other, carefully checking to make certain the creased
portion of the tape aligns with the corner of the joint.
Then smooth both sides of the corner.
Apply a second coat of wallboard compound with a corner
trowel. After the second coat dries, apply a final coat of
compound and smooth it with a wet sander.