Before you learn how to finish them, it's important to understand what a butt joint is. In short, the long edges of drywall sheets are tapered while the short edges are not. Where two short, non-tapered edges meet is called a butt joint.
Butt joints are challenging to finish because they require that you build a slight, gradual mound to hide the joint. To make the mound subtle enough to go unnoticed, you must feather the joint compound over a wide area. You can also minimize the difficulties of concealing butt joints by using a back blocking technique when hanging the drywall. We'll show you the best way to finish drywall butt joints, plus provide a few helpful pointers.
The color-coded drawing gives you an idea of what you're trying to accomplish with each coat on a butt seam.
The first coat, indicated in blue, should be as thin as possible over the tape. If you use fiberglass mesh tape, it's fine if you still see the texture through the compound. Use the center of this seam as the reference line to feather the second and third coats further outward on the wall. You want to deposit as little compound as possible along the seam. Concentrate on feathering outward from the center.
Apply the second coat (white) with a 6-inch knife. Make a 6-inch swipe to both sides of the joint's centerline.
You'll apply the third coat (coded red) with a 12-inch knife. Feather 8-10 inches outward from the centerline.
Cover the butt joint with fiberglass mesh tape. Use your 6-inch knife to cover the tape with mud.
When the first coat of mud is dry, apply the second coat along both sides of the joint using a 6-inch drywall knife.
Apply the third coat with a 12-inch drywall knife, feathering the edges out 8-10 inches on each side of the joint. You may leave a ridge down the center, but it can be scraped away later.
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