When installing drywall flat against a stud, there are two types of drywall joints, or seams, you can make: the butt joint or the tapered joint. In many cases, the type of joint you use is dictated by the application. But in a few instances, you may have a choice between butt and tapered joints.
What a Butt Joint Is
A butt drywall joint is created when the edges of the two sheets of adjoining drywall have the same thickness as the rest of the drywall sheet. For example, if the sheet is 1/2-inch thick, the edges of the sheet will also be 1/2-inch thick. If these two 1/2-inch edges come together, this is a butt joint. These edges are located on the short (or the 4-foot long ends) of the drywall sheet.
What a Tapered Joint Is
A tapered joint is when the edges of two sheets of adjoining drywall taper from the rest of the sheet’s thickness to a reduced thickness. If the sheet is 1/2-inch thick, these reduced thickness edges will be thinner (actual size varies). On average, the tapered edge of most drywall is about 1/8-inch thinner than the rest of the drywall. So, when these two thinner edges meet, this is a tapered joint. These edges are located on the long (or the 8-foot long) ends of the sheet.
Which Drywall Joint Is Best?
Whenever you have the choice, choose the tapered drywall joint. A tapered drywall joint will nearly always look better than a butt joint. Tapered joints allow you to fill in the valley created by the tapers with drywall tape and drywall compound, thus creating a smooth, visibly seam-free joint. The joint is still there but it is buried underneath the drywall compound. Among many advantages, one benefit of tapered joints is that they are easy to build. The joint is designed so that the joint compound fills only the valley and no areas beyond the valley. There is no guesswork with tapered joints. The downside of tapered joints is that they require much more joint compound than butt joints. Butt joints will always initially produce a ridge. In many cases, though, you will have no choice but to use a butt joint. In this case, with careful application of compound and sanding, butt joints can be made to disappear.
Butt Joint Installation
The name butt joint comes from an installation process when two non-tapered sheets of drywall are butted up next to each other. A thin coat of drywall compound is laid down, then drywall tape is embedded in the compound. Then another thin layer of compound is spread over the tape. This compound is smoothed over with a drywall knife, sanded, and often applied with a second coat of compound. Professional drywallers often install drywall shims (1/16-inch-thick strips of paper) to the adjacent studs on both sides of the stud where the butt joint is. This creates a slight depression that can be filled without the appearance of standing out.
Making a Tapered Drywall Joint
If you look carefully at the long edge of drywall, you will notice that on each side there is a taper. It is nearly always preferable to choose the tapered joint over the butt joint in flat (not a corner) seam installation. This is because the joint compound can be used to fill in the taper. A drywall taper is formed when the tapered edges of two sheets of drywall are adjoined. Together, the two tapers form a triangle. This triangle drywall taper will allow for drywall tape and joint compound to be filled in, without leaving any kind of bulge. Whenever possible, you should make tapered joints because the seam is nearly invisible. Note that the drywall taper is only for flat installations, not corner installations. Using the tapered edge of a drywall sheet on corners will produce corners that are not perfectly 90 degrees.
Filling the Tapered Drywall Joint
The tapered drywall joint results in nearly invisible seams because the mudding compound perfectly fits in the valley and does not rise above the level of the drywall facing. With the tapered drywall joint, you can even use a stronger type of tape, such as mesh fiberglass drywall tape. You would not want to use fiberglass mesh on butt joints because it is fairly thick and will result in bulges. Paper drywall tape embedded with joint compound is strong enough to hold the joints together.
