Matt is a professional painter and freelance writer, sharing his knowledge, house-painting tips, and product reviews.
Skim Coat Drywall for a Smooth Paint Job
Skim coating is the process of applying thin layers of joint compound to fill in gouges and small holes from drywall damage. Skim coating is often done for the purpose of smoothing out textured walls, or fixing damage that occurs when removing old wallpaper. Aggressive scraping and chemical cleaners soften and tear open the paper facing of drywall.
The spiked rollers on those wallpaper remover tools, such as the Paper Tiger, puncture drywall with thousands of tiny holes, and those holes show through new paint when left unfilled. Paint alone won't fill them. Fortunately, you can make your walls look new again with a little elbow grease.
- Canvas drop cloths
- 6-inch taping knife
- 12-inch taping knife
- Empty 5-gallon bucket
- Drywall sanding sponges
- Painter's plastic and tape
- Wall cleaner (TSP, Dirtex powder, Dif)
- Easy Sand powder compound (90 minute)
- Step ladder
Skim Coating vs Replacing the Drywall
If your walls are severely torn open and in terrible condition, especially from water damage, you might consider tearing them out and installing new drywall instead of repairing them. The walls might be too far gone, or if water damaged, you could have mold growth. Sometimes it's better to replace the walls, depending on the severity of the damage.
Walls are not the only surface you can skim coat. Maybe you want to get rid of heavy roller stippling on a painted door, or smooth out noticeable paint brush marks on molding. You can repair almost any painted surface with a skim coat.
Scrape and Clean the Drywall
To get a smooth finish with your coats of joint compound and paint, remove loose pieces of torn drywall paper. If you don't remove all of the loose pieces, air gets trapped underneath and forms bubbles when you prime and paint. Bubbles are a pain to fix because you have to scrape them off, patch again, and repaint.
- Scrape off torn drywall paper. Use a 6-inch taping knife to scrape the wall and remove loose pieces of torn drywall paper. Grab the edges of the loose ends with your fingers and tear them off.
- Clean the walls. Whether you're skimming over textured walls, or removing paste from wallpaper, cleaning the walls is important. Wallpaper paste shows through paint if you don't wash it all off. Sometimes you won't even know paste is there until you paint the walls. There are several good cleaning products to use. TSP, or even fabric softener for clothes, dissolves wallpaper paste. Rinse the walls with clean water.
- Sand the walls. Once the walls have dried from cleaning, use an orbital sander with fine grit sandpaper, or a drywall sanding sponge, to sand the walls smooth. Check the edges around gouges and holes and make sure there isn't any torn drywall paper above the surface. The walls have to be smooth.
Prime the Walls Before Skim Coating
To get the best results, two prime coats are needed for this project. Apply the first coat before applying your first skim coat. The second prime coat is applied over the final skim coat. Painting directly over drywall joint compound without priming first reduces the quality of the paint finish. Drywall mud is very porous and spongy. The primer forms a sealed layer so the paint dries evenly for the best finish.
Why prime before skim coating walls?
Primer is important because it acts as a surface sealer and base coat for the drywall mud. A prime coat is critical for sealing stains and exposed drywall paper. If you scraped the wall too hard and tore open the brown paper beneath the surface of the drywall, the water in the joint compound will soak into the paper and form bubbles, unless you prime first.
The Best Primer for Damaged Drywall
Prime damaged walls first with oil-based primer. Oil primer is messy to work with and smells bad, but it's an amazing sealer for paint. Do not use latex primer on torn open drywall paper. Latex primer will cause the paper to bubble. My favorite primer I've used many times for damaged walls and water stains is Cover Stain oil-based primer. The primer block stains and prevents bubbles from forming over torn open drywall paper. You can skim coat and paint over oil primer without any problems.
For walls in good condition, without water stains, or torn open drywall paper, you can use latex primer. In the case of peeling paint, primer specially formulated to prevent peeling is best, but for basic priming, I really like the latex Prep Rite Pro Block, or the Drywall Primer, both from Sherwin Williams. The Drywall Primer is cheaper and works great for priming new drywall and hole repairs on walls. To prevent problems with damaged walls, spot priming the damage with oil primer is your best bet for the first coat. Use latex primer the second coat over the skimmed walls at the end.
Skim Coat Your Drywall Two Coats
Two coats of drywall compound is usually enough to smooth out textured walls and shallow holes, but deep gouges usually need a third coat to make the holes level with the surface of the wall. Sanding is necessary between coats. The fastest way to apply drywall mud over an entire wall is with a paint roller.
The Best Drywall Mud for Skim Coating
For skimming and most drywall repairs, I use the bagged Easy Sand drywall compound from the Sheetrock brand. Use the 90-minute version to extend your working time, so you're not rushing to get it on the wall before it dries. I'm not a fan of pre-mixed drywall mud sold in buckets. These usually take longer to dry and shrink too much. Easy Sand dries harder with less shrinkage. It also sands easily as long as you don't apply heavy coats.
- Mix up your drywall compound. You'll need an empty five gallon bucket, powder joint compound (Easy Sand), and a drywall mud mixer. Mix up the compound in the bucket with warm water. The consistency of the mixed compound should be similar to cake batter. The mud should not be watered down, or chunky. Make sure it's thoroughly mixed before rolling it onto the walls.
- Roll the compound onto the walls. Use a 9-inch, lint-free, paint roller with 3/4-inch to 1-inch nap thickness. The purpose of the roller is only to get the mud onto the walls. Rolling on the compound is a lot faster and easier than using only a taping knife. Don't apply the compound in thick coats.
- Skim coat the walls two to three coats. With a 12-inch taping knife, skim off the excess compound from the top of the wall to the bottom. Be sure not to leave chunks and heavy edges in corners otherwise it will be hard to sand them smooth after drying. The walls should be skimmed in very thin layers to make sanding easy and the dry time faster. One coat alone isn't enough. I recommend applying at least two coats to get the best results.
- Set up a dust barrier before sanding. Drywall mud produces a ton of nasty dust when sanded over the entire surface of walls. Controlling the dust is critical, especially when working in an open space without doors that can be closed. Seal off nearby return vents so the dust doesn't migrate to other rooms. You can tape painter's plastic from the ceiling to the floor to create a dust barrier, or use extension poles to keep the plastic up without worry. I own and use several Zip Wall poles for drywall repair work and spray painting projects. These poles are well worth the investment if you do a lot of drywall work and sanding. Not having to tape plastic to the ceiling anymore was a game changer for my projects.
- Sand between coats. A light sanding is essential for each coat of drywall compound applied. Sanding the skimmed walls smooths out the rough texture of drywall mud. Don't use an electric sander. It will produce too much airborne dust. Use a sanding sponge to sand the walls smooth.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Matt G.