Prepare for Dust—Lots of It!
Drywall sanding is one of the worst jobs in construction. It’s not only dirty and grueling, but also stressful because now you have to fix any earlier mistakes. Good sanding results are built on the foundation of good taping, and the final sanding is your last chance to get the whole job right. The paint job will reveal the truth: Either you succeeded—all the fasteners and seams look uniformly invisible—or any taping and sanding flaws are now glaringly apparent forevermore. No wonder so many homeowners choose to hire out drywall work. Take heart: If you’re patient and pay attention to detail, you can tackle this job! We’ll show you the sanding steps and finishing techniques the pros use to get sanding done quickly with excellent results.
Drywall dust is fine, like flour, and will travel to other areas of the house. To prepare your house for the work ahead and reduce this dust, follow these steps:
- Lay dropcloths. Use plastic sheeting and masking tape to seal off cold-air return ducts and doorways. Mount box fans in windows (exhausting out) to ventilate the room. Remove the screens from your windows and doors before starting work to avoid having to clean drywall dust from them afterward.
- Get the proper safety equipment: a two-strap dust mask (changed every half hour if you’re working in under-ventilated areas) or a respirator—both types rated for drywall work—plus a hat, glasses (goggles fog up) and comfortable clothing.
- Don’t forget the psychological aspect of drywall sanding: The work goes much quicker and easier if you recruit a helper and turn on your favorite music!
“Map” Walls and Ceilings First
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Photo 1: Map the wide seams
“Map” all wide seam work on ceilings and walls to plan how much to sand each seam. With a backlight positioned on one side of a wall or ceiling, place your taping blade across the end of a seam, slide the blade along the seam, then, every 4 ft., label the spots “high,” “fill” or “even.”
Before sanding, round up a “shadow light” (Photo 1), a wide taping blade and a pencil (not a felt tip pen; it bleeds through paint). Using these tools, survey (“map”) the flat seams and outside corners throughout the room. I use the following labeling codes:
High. If lighting reveals a high spot in the middle of the seam, sand the high spot down so the seam is uniform and even. Avoid sanding off so much joint compound that you expose and scuff the underlying drywall tape. If that happens, use a wide blade and more mud to build out the seam from the high spot to both outside edges, let the mud dry, map the seam again and then sand it.
Fill. If light shows only at the middle of the blade, the seam needs more “mud” fill. Recoat with more mud and let it dry before you sand it. Use an “easy-sand” joint compound, which is available at home centers and hardware stores in 25-lb. bags of powder that you mix with water. Add the mud, let it dry, then sand the seam; you can usually do it the same day.
Even. If light is uniformly blocked along the length of the blade, sand the seam minimally and evenly.
Two Tools Handle the Bulk of the Sanding Work
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Photo 2: Apply even pressure
Apply an even-pressure, push-pull motion to work a hand sander inside the flat seams and along the narrow vertical nail/screw patterns called “strips.” Work the edges of the seams or strips with this push-pull stroke or use a circular, buffing motion to “feather out,” or smooth, the transition edge between the seam and the bare drywall.
Note: We used water-resistant drywall because its green color provides more visual contrast between the drywall, the taped seams and the strips. Don’t use water-resistant drywall on ceilings (it sags). Also, check with a building inspector; many areas do not permit its use on exterior house walls.
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Photo 3: Using a pole sander
Use a push-pull stroke with a pole sander. Your arms may turn to rubber, but using a pole sander is faster and easier than working a hand sander from a ladder. Turn the head of the pole sander wider to work across seams or narrower to sand along fastener strips. Carefully sand the transition edge between the taped seams/strips and the bare drywall to avoid scuffing the drywall’s paper face.
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Photo 4: Three common problems
Be aware of three common problems as you sand: Hide a protruding screw (or nail) by first setting the fastener properly below the drywall’s surface and then applying two coats of easy-sand mud. Knock off a ridge of dried joint compound on a seam with a small taping blade and smooth the surface with one thin coat of easy-sand mud. If you have a thick buildup on a transition edge, avoid heavy sanding because you’ll likely scuff the adjacent bare drywall. Instead, use a 6-in. blade to feather another layer of easy-sand compound around the inside corner where these two seams meet.
For 80 percent of your work, you’ll use a hand sander on the lower walls (Photo 2) and a pole sander on both the high portions of walls and all ceilings (Photo 3). NOTE: All the drywall tools discussed here are available at home centers and most hardware chains. Set up work lights so they shine across the seams to highlight flaws in the taping work. Spend the time now to perfect your sanding; it’ll pay dividends once you paint and must live with the results.
Use an even-pressure, push-pull motion to work the hand sander. To smooth out shallow scratches in a seam or screw/nail pattern (called a “fastener strip”), use light pressure on the hand sander and move it in a circular buffing motion. Pole sanders are more difficult to control; use either the push-pull motion or a side-to-side sweeping motion. Twist the handle to control a ball joint on the sanding head that will shift the movement of the head and allow the sander to both switch directions and turn around the inside corners where seams meet. Avoid scuffing or chafing the paper surface of the drywall—those flaws may be visible after painting. The edges of all seams and fastener strips should look soft and smooth after they’re sanded.
Confine hand and pole sanders to the “field” of a wall or ceiling. If you work too close to inside corners, these tools may slam into adjacent walls, denting or gouging the finish. The pole sander, with its ball joint in the sander head, is prone to flip over (“jackknife”) and cause damage. Both tools accept disposable, custom- sized sanding screens (which come in one choice of surface coarseness, or “grit”) or sheets of sandpaper (various grits). Use these tools to quickly grind down high spots or smooth the even spots on all flat seams, outside corners and fastener strips.
Some pros use “open mesh” sanding screens, but most do-it-yourselfers should avoid them. The open mesh allows the drywall dust generated during sanding to pass through and off the sander. However, screens are prone to leave scratches on the finished surface and wear out faster than sandpaper.
Most workers get the best results from 150-grit drywall sandpaper. The pores of drywall sandpaper may appear to be clogging during use, but drywall dust actually becomes an additional abrasive to both grind and polish the taped surface, yielding a smoother finish and extending the life of the sandpaper. However, for easier and speedier sanding, you’ll still need to change sandpaper sheets frequently (an average-size bedroom will take three or four sheets of sandpaper).
Certain problems crop up during this stage of drywall sanding. Use the tips in Photo 4 to solve them.
Final Sanding Work and Preparation for Painting
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Photo 5: Sand with a light touch
Control sandpaper with an easy, light touch to avoid scuffing and gouging the surface finish. If your sanding does uncover and then scuff joint tape, apply more mud, feather it out, let the mud dry and carefully sand again.
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Photo 6: Using a sanding sponge
Firmly grip an angled sanding sponge, apply steady pressure and move it up and down inside corners for a straight, well-defined edge. Then move the sponge in either a push-pull or circular motion to feather the transition edge of the finished corner seam.
Once you’ve done the bulk of the sanding, switch gears and tools to finish tricky “finesse” areas like those around electrical outlets or lights, and inside corners. You can choose a hand sander for finesse work, but a better choice around outlets is handheld sandpaper (Photo 5). Hand sanders work great on inside corners, but while smoothing one side, you may end up over-sanding the opposite side, cutting a deep channel that will require a touch-up of mud to fix. Instead, use a fine-grit, angled, wet/dry sanding sponge to work each side of the inside corners (Photo 6).
Preparation for Painting
In the past, after sanding my drywall, I prepared for painting by either sweeping the surfaces or vacuuming them to clean off all the dust. Wrong, say many experts. They advise minimal wall and ceiling cleaning. Sweep off the accumulated dust from the inside corners and any dust balls from wide taped seams and fastener strips. Otherwise, leave an even coat of dust over the entire drywall surface, especially along the transition edges of the seams and fastener strips. The dust will bind with the paint and provide a filler to mask scratches, pinholes and chafed surface paper.
Dust—your opponent throughout the early stages of drywall work—ironically becomes an ally at the end to improve the paint job and help deliver the fine results you’ve worked toward.