Finishing Drywall Butt Joints

Finishing Butt Joints

The long edges of drywall sheets are tapered. Two tapered edges together form a depression, which makes it possible to create a flat mud joint. The short edges of drywall sheets are not tapered; they meet at a butt joint.

Butt joints are more 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.

The same fiberglass mesh tape and similar techniques for applying mud are used for butt joints and tapered edges.

Apply the second coat of compound to the vertical butt seam after you've completed the second coat on the horizontal tapered seams, as shown in Step 2. That way, you'll do a better job of blending the intersection.

To minimize the difficulties of concealing butt joints, consider using a back blocking technique when hanging the drywall.

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Tapering the Butt Joint

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.

Step 1

Cover the butt joint with fiberglass mesh tape. Use your 6-inch knife to cover the tape with mud.

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Step 2

When the first coat of mud is dry, apply the second coat along both sides of the joint using a 6-inch drywall knife.

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Step 3

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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Check the Butt Joint

Use the edge of a 12-inch knife to check your progress in tapering a butt joint. With the middle of the blade at the centerline of the seam, an ideal seam will be nearly flat over the full length of the blade. If you see light between the blade and the wall or if the blade rocks more than 1/16 inch in either direction, apply another coat. Again, taper from the centerline toward each side.