Drywall 101: How to Finish Seams and Joints with Drywall Tape - Wallboard Trim & Tool

Drywall 101: How to Finish Seams and Joints with Drywall Tape

Drywall 101: How to Finish Seams and Joints with Drywall Tape

If you’re working on a home renovation project, odds are you’re going to be installing drywall. The first part, hanging the drywall, is fairly easy, straight forward, and just requires a bit of time, attention, and a few tools. Taping and mudding the drywall – called “finishing” the drywall – takes a bit more practice.

The difficulty of finishing comes mostly from the fact that it directly impacts the final result and mistakes in finishing will be apparent in the appearance of the finished wall. Besides the aesthetic value, taping and mudding are also important because they are the steps that join the individual drywall boards into a single, uniform surface and are thus crucial for the long-term strength of the wall or ceiling. Good finishing will help the surface stay looking good, smooth, and crack-free, avoiding costly and time-consuming repairs later on.

The basic process is simple, but it requires confidence and a steady hand. Here’s what you’ll need to know.

1. Joints

The first thing you’ll finish is the seams between the drywall boards themselves. The long sides of the drywall are tapered to facilitate the finishing process and are considerably easier to tape and mud. Start with these because you’ll need some practice before you do the “butt joints” where drywall sheets meet at the (un-tapered) short end.

First, you’ll use mud to fill and cover the seam between the two boards. This is where the tapered edges make things easier. They create a natural valley where you can easily put the mud without creating a bump in the overall surface of the wall.

Once you’ve laid down your first layer of mud, you’ll cover the seam with drywall tape, pressing it in every foot or so and then smoothing it from the center of the seam outward towards the ends. Use a small knife (6-8”) to do this step, pulling with a gentle, smooth pressure to simultaneously smooth the tape and press it into the applied compound. The tape should be embedded in the compound but don’t press too hard, as you can deform the compound filler which will require you to go back and fill again later.

Once you’ve embedded the tape, apply a second coat of mud over top of it using a 10” taping knife. As before, start at the center and work towards the ends. Use a smooth, gentle pressure to feather the compound outward, creating a smooth, thin surface that covers the tape and gradually tapers away to the board beneath.

Let everything dry overnight before coming back to do a third coat with a 12” taping knife. For the third coat, thin the compound with a little bit of water until it is roughly the consistency of mayonnaise. This thinned compound will be able to penetrate into any holes or irregularities in the previous layer, creating a smoother, stronger result. Apply the third layer like the other two, spreading and feathering the compound with a gentle, even pressure from the center to the ends. 

Let the third coat dry overnight. The next day, sand away any irregularities in the surface using courser sandpaper to start and then progressing to finer grit sandpaper to finish. This will allow you to create a perfectly smooth surface that tapers imperceptibly down to the drywall beneath.

When finishing butt joints, follow the same basic steps as for tapered joints but be aware that you’ll need to be very careful to apply the right amount of mud. You need enough to create a good bond. On the other hand, too much compound at the beginning will create a bulge that will be nearly impossible to hide later on. Careful feathering will be required here to hide the joint, so do these seams after you’ve practiced your technique on the easier joints. Butt joints will be wider than tapered joints as you need to feather out the mud over a larger area to create a smooth-looking finish. 

2. Inside Corners

Taping inside corners follows the same basic steps as taping drywall seams but you may want some special tools. As with flat seams, you’ll lay in some mud, embed the tape, and then cover the tape with several more coats of mud before sanding.

The difference is that you’ll need to use one piece of tape positioned over the center of the corner seam to join the two sides of the corner together. Fortunately, most paper drywall tape comes with a seam down the middle that can be used to fold it exactly in half, creating a natural corner in the tape that you’ll fit into the corner on the wall. This seam presents a slight bulge towards the outside of the tape and the bulge side should go against the wall. You should also strongly consider getting a corner trowel/knife, which looks like two knives joined at a right angle. This tool allows you to smooth both sides of the corner at the same time, ensuring that both sides get the same treatment and saves you steps.

Lay in a smooth, thin, lump-free layer of compound on each side of the corner and fill in any gaps between the two sides. Next, cut your tape to length and fold it at the seam, making sure that the bulge is towards the wall side. Use the longest length of tape you can comfortably handle and if one corner needs multiple pieces, overlap the ends slightly. Draw your knife across each side of the tape to lay it into the compound (or use the double-sided corner knife to do both parts at once). Lay in a second coat of compound on each side of the corner and let it dry. If you don’t have a corner knife, do one side of the corner completely before starting the other side. Once the compound has dried, do a third coat with thinned out compound as you did for seams. As with normal seams, use a wider drywall knife for each subsequent coat to feather the compound out gradually from the joint.

3. Around Windows and Doors

Windows present a mix of the finishing tasks you’ve used so far: a window fitting will probably require inside corners, outside corners, and flat seams. You’ll do the flat seams and inside corners basically as you would for the walls: apply mud and fill gaps, embed the tape, apply and feather cover coats before sanding smooth. Fixtures like windows and doors will also involve outside corners but those are better finished with corner bead (instead of paper tape). For more on outside corners, check out our corner guide.

The same goes for doorways: you’ll need to finish the outside corners of the opening with a protective corner bead but the rest will be familiar work from the seams and inside corners you’ve already done.

Summary

Finishing drywall is a bit more difficult than hanging it and requires confidence and practice. Still, any craftsperson who has hung drywall successfully and is ready for the next challenge will find that taping and mudding are well within reach if they are willing to put in some time learning the skill. Anyone who is just starting out in drywall finishing should begin with tapered seams, as they are the easiest to complete and will provide a valuable opportunity to practice feathering the drywall compound and applying the right amount of pressure before moving on to more delicate tasks like butt joints and corners. Finishing windows and doors with paper tape will involve a mix of flat seams and inside corners, while outside corners are better finished with corner bead.

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