Finishing A Lot Of Drywall With Only A Little Sanding


August 24, 1991|By Karol V. Menzie and Randy Johnson

If you've ever watched a pro finish drywall, you probably thought to yourself, "I can do that." And probably the first time you tried it -- and the tape didn't stick, and the joint compound had lumps and the ridges wouldn't ever go away -- you thought, "I can't do that."

Actually, you probably can do it. Once you know what pitfalls to avoid and have gotten in a little practice, you should be able to finish a lot of drywall with only a little sanding.

Sanding is the key. It's labor-intensive, time-consuming, messy and bor-rrring. The less you have to do, the better you can rate your technique.

Don't start out thinking you'll find shortcuts. Shortcuts are exactly what create a bad drywall job. Set your mind to the painstaking process of following every step completely and thoroughly, and you'll be rewarded with a wall that is virtually indistinguishable from plaster.

There are three stages to a finishing job (four counting cleanup). Ideally you will complete one before going on to the next. In reality, you may be on Stage 1 in one spot and Stage 3 somewhere else. If you start getting confused, pencil a note on the wall.

Stage 1, the base coat:

1. Open the compound and mix it up with a drywall mixer or a clean strong stick. You want the compound you apply to be as smooth as possible. Scoop up a couple of cupfuls on the knife and put it on the hawk (a flat metal or wooden plate with a handle in the bottom) or in the joint compound pan. Make sure there aren't any lumps. You may want to add a few drops of water and mix it up thoroughly, to get a creamier consistency.

2. Use a 4-inch drywall knife to spread a thin layer of compound over the seam. (If the drywall has been hung properly, most of the seams will join two beveled edges, so there is a slight depression. Some butt joints are unavoidable, and they're harder to finish because you are starting out with a flat surface. The first layer of compound should be as wide as the knife with no gaps or bare spaces, and somewhere between 1/16 and 1/8 inch thick.

Measure off the paper drywall tape. You can cut it with a knife or scissors, but the standard way is to tear it against the edge of the knife. (Make sure the knife is clean and use a hard, flat surface underneath.) If it's a long seam, you may want to do it in two or three pieces, overlapping the tape just slightly where it joins. On a vertical joint work from the top down; on a horizontal one, determine whether you're more comfortable starting at one end or starting in the middle and working out in both directions.

Embed the tape in the compound by pressing it with the blade. Try to use long, smooth strokes. The point is to avoid any bubbles or creases. It may take a couple of hard passes to get the tape thoroughly embedded. Force the compound to ooze out from under the edges of the tape and press out any bubbles. Bubbles tend to travel ahead of the knife. If a bubble seems too big to simply press out, stop, hold the tape with the blade, and lift it from the end back to the bubble, then re-embed it.

On inside corners, fold the tape along the groove, apply a thin layer of compound to each side of the corner, then embed the tape, working on one side at a time. On outside corners, apply a metal corner bead, nailed extensively on both sides to get it flat and tight to the surface. If the corner bead isn't flat enough, you'll have problems later. Apply joint compound to each side with the 4-inch knife; scrape off excess. (Don't worry if the edge is a little rough. That's one place you invariably have to sand.)

3. Once the tape is embedded, scrape off the excess compound with the 4-inch knife so the joint is smooth and the tape is showing. This step is important -- if you don't remove the excess, you will have to sand it later.

4. Let the embedded tape dry thoroughly. It usually takes at least 12 hours. (It will take longer if humidity is high.) Don't rush it. Don't touch it until it's dry. If you were careful when you scraped off the excess, you won't have to sand at this point. (If you do have to sand some spots, avoid sanding the tape. It will fuzz up the surface and make it harder to cover.

Stage 2, the block coat:

1. The goal of this coat is to cover the tape or corner bead. On the corner bead, use a 6-inch drywall knife to apply a second, thin coat of compound. Don't apply too much; you'd just have to sand it off later. On the joints, use the 6-inch knife to fill the bevel and just cover the tape. Hold the knife at an angle of about 30 degrees from the surface on the compound side. Use long smooth strokes and try to make the compound surface as flat as possible -- not concave or mounded.

It's hard for an amateur to do both sides of an inside corner at the same time, unless you become adept at using a corner knife. We prefer to finish one side at a time. It takes longer in hours, but it may be shorter in terms of actual labor.

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