The Ultimate Guide To Skim Coating: Mastering The Art Of Wall Transformation

Skim coating is a great way to smooth out or repair damaged walls. It involves applying a thin layer of diluted joint compound (also known as mud) to the wall to create a fresh surface. The process is relatively easy and can be done by novice drywall workers or homeowners. The number of coats required depends on the condition of the wall and the desired finish. Typically, two to three coats are applied, with each coat dried and sanded before the next one is applied. The cost of skim coating varies depending on the size of the room and the extent of the damage but typically ranges from $300 to $1,200.

How Many Coats to Skim a Wall

Prepping your walls

Before you start skim coating, it's important to prep your walls to ensure a smooth finish. Here are the steps you should follow:

Clean the walls: Start by giving your walls a thorough cleaning, especially if you're removing wallpaper paste or paint. Use a wall cleaner such as TSP, Dirtex powder, or Dif, or even fabric softener, to dissolve any wallpaper paste. Then, rinse the walls with clean water.

Scrape and repair the walls: Use a taping knife to scrape off any loose pieces of torn drywall paper. Grab the edges of the loose pieces with your fingers and tear them off. Pay special attention to areas with gouges or holes, and make sure there isn't any torn drywall paper above the surface.

Sand the walls: Once the walls are dry, use an orbital sander with fine-grit sandpaper or a drywall sanding sponge to sand the walls smooth. This step is crucial for achieving an even finish.

Prime the walls: Priming your walls is essential before skim coating. Apply one to two thin coats of a suitable primer, such as Zinsser's Bulls Eye 1-2-3 primer, to seal any loose paper and promote better adhesion for the joint compound. Let the primer dry thoroughly before proceeding to the next step.

Mix the joint compound: Choose an all-purpose or lightweight joint compound, depending on your needs. Mix the compound in a bucket according to the manufacturer's instructions. Aim for a consistency similar to mayonnaise or yogurt—not too watery or chunky.

Apply a base coat: Before skim coating, consider applying a thin base coat of the joint compound to the entire wall. This will help fill in any small holes or imperfections and create a more even surface for your skim coat.

By following these steps, you'll ensure that your walls are properly prepared for skim coating, which will help you achieve the desired smooth and seamless finish.

Applying a skim coat

First, prep your walls by covering furniture, woodwork, and floors with plastic sheets or drop cloths. Move all your furniture to the centre of the room or out of the room. Then, cover doorways and your woodworking with plastic sheets held in place with painter's tape. Remove cover plates from light switches and wall sockets to keep them splatter-free.

Next, fill in any holes or cracks in your wall with spackle. Use a putty knife to press the spackle into the holes, cracks, or nicks to repair your walls. Give the spackle about 1-2 hours to dry before moving on with your repairs. If you're doing a skim coat on plaster with cracks, apply joint tape over them to keep them from spreading. If you're repairing holes larger than 1 inch (2.5 cm), apply a drywall patch to fill it in.

If your walls have glossy paint, sand them with 220-grit sandpaper to scuff it up and remove the sheen. Skim coats work fine over any primer or matte paint, but glossy paint prevents them from sticking to the surface. It's okay to apply a skim coat directly to drywall even if it doesn't have paint or primer.

Clean your walls thoroughly with a damp sponge or towel to remove any dust or residue. If your walls have stuck-on grime or residue that you can't remove with a sponge, apply a commercial surface-cleaning product and gently scrub the surface. Rinse the wall with clean water after using any cleaning product.

Now, it's time to mix your joint compound. Mix the joint compound with water until it has a yogurt-like consistency. Follow the directions on the package and use an electric drill with a paint paddle attachment to mix the compound. Gradually add water until there aren't any solid lumps. Mix your compound in small batches since it could start drying out before you apply it.

Apply the compound to a section of your wall with a paint roller. Start with a 3 ft x 5 ft (0.91 m x 1.52 m) section and press the roller firmly against the surface. Apply firm, even pressure as you roll the joint compound up and down your wall. Rewet your roller when it dries out and keep spreading until you completely cover the section.

Smooth out the skim coat with a drywall knife. Hold the knife along the leftmost edge of the section, with the left side of the knife slightly closer to the wall than the right. Pull the knife straight down to smooth out the joint compound, slightly overlapping the area you just smoothed. Continue working in columns across the section of your wall.

Continue applying the skim coat in sections across your wall. After you finish one section, move on to the next, applying the compound with your roller and then smoothing it out with the drywall knife. Keep working until you've applied a single coat to your entire wall.

Let the first coat set for 4-8 hours, or overnight. It will normally be dry enough for a second coat in about 4 hours, but it may take a full day if the coat was thick or humid.

Sand the walls with 220-grit sandpaper to smooth out any rough or raised edges. Shine a light from the side to help you see any imperfections. Wear a face mask and protective eye gear when sanding to avoid irritating your eyes or lungs.

Apply a second layer of joint compound in the opposite direction. Roll the compound on horizontally so it's perpendicular to the first coat. Work in small sections, putting compound on and smoothing it out. Once you've coated the entire wall and it looks smooth, let it dry overnight.

Keep adding new coats of mud until your wall looks smooth. Lightly sand your wall with 220-grit sandpaper before each coat, switching directions between coats from horizontal to vertical. Just make sure to let the compound dry overnight before applying the next layer. It usually takes 3-4 coats to smooth out your wall completely.

Finally, put a coat of primer on your wall before painting it. Joint compound and drywall absorb paint and hold colour differently, so apply a coat of primer to the surface. Use a roller to spread a thin layer of primer over the wall and let it dry for a few hours before applying a second coat.

Using a roller or sprayer

Skim coating with a roller or sprayer is a popular application method. The drywall compound can be applied quickly, and cleanup is easy. You can also use a drywall knife to smooth down the drywall compound after application. However, this can be a slow and laborious process.

Before you begin, it's important to prepare the work area. Cover any areas that will not be skim-coated. Shut off electrical circuits to outlets and light switches, and remove faceplates. Tape the outlets and switches with painter's tape. Lay down drop cloths and tape them to the wall baseboard.

Next, you'll need to mix your drywall compound. Use a light-body compound and follow the mix ratio instructions on the product. It's often better to use slightly less water than specified to create a heavier, stickier product. Mix until you have a stiff, yogurt-like consistency.

Now you're ready to roll out the drywall compound. Work in sections of about 2 feet wide by 8 feet high. Press the roller firmly into the wall to remove any bubbles. Keep the compound consistent across the surface to avoid drying at different rates.

If you're using a roller, you'll need to apply 2-3 coats, letting each one dry in between. Use a 1/2-inch nap roller to apply the compound in small sections of about 4 feet square. Try to keep the application as even as possible.

If you're using a sprayer, rent a texture sprayer rather than a standard paint sprayer. You'll still need to follow the same process of smoothing the compound with a drywall knife after application.

Once you've finished applying the compound, let it dry. This should take about 1-2 hours. Then, finish with a light sanding using fine-grit drywall sandpaper.

Smoothing the compound

The first coat won't be perfectly smooth. The compound is filling the voids around the raised surfaces in the existing texture. If you have a really heavy texture, you'll need more layers of joint compound. Each coat of mud should be smoothed in the same direction as it was applied onto the wall with the roller. Alternate the direction of each consecutive coat. If you rolled the mud onto the wall vertically on the first coat, switch to horizontal application for the next coat.

After rolling the mud onto your first section, use a trowel to smooth it out. The trowel is like a squeegee and does come with a cover over the blade. Make sure to remove the blade cover! Use a damp rag or spray bottle to wet the blade before use. Pull the trowel over the compound, smoothing it out. Squeegee the mud in the same direction that you applied it with the paint roller.

You can lightly sand between coats, but it's not necessary. Each consecutive coat with the trowel will make the wall smoother. If anything, you may have lines created by the excess mud sliding off the edge of the trowel as you skimmed over the wall. These lines are easy to get rid of with a quick sanding. If you find a big blob of dried mud, you can scrape it off with a drywall knife.

Shining a light at an angle on the wall you're working on will help you see imperfections. This is true when priming and painting, too. When you think you're done, move the light so it shines from a different angle. You'll be surprised to see how many areas you missed.

Tips for Smoothing the Compound

• If you're using ready-mix mud, add a little water at a time so you don't end up making it too runny.
• If the mud does end up too runny, add more of the dry mix.
• Work in small sections at a time. The mud is watered down, so it will dry fairly quickly, and you'll have to apply it to the wall and then skim it smooth.
• Using a roller allows you to get more compound on the wall faster than if you were scooping it out with a putty knife.
• You can pour joint compound into a roller tray or dip the roller directly into the bucket.
• The bucket method is faster but messier because the excess mud drips off the roller as you pull it out.
• If you have really heavily textured patterns, the first coat won't produce perfectly smooth walls. The trowel may create gouges or new lines. Don't worry—the next coat will fix that.

Sanding the dried skim coat

Allow the skim coat to dry

Before you begin sanding, make sure that the skim coat is completely dry. Depending on the temperature, humidity, and airflow in the room, the drying time can vary. Typically, it should take around an hour or two for the skim coat to dry. It is important to be patient and not to rush this step, as starting the sanding process too early can lead to uneven results.

Choose the right sandpaper grit

For sanding the skim coat, it is recommended to use fine-grit sandpaper. Specifically, you can opt for 120-grit sandpaper. However, if there are too many peaks and valleys on the wall, you may need to start with a coarser grit, such as 100-grit, to initially level out the surface before proceeding with the finer grit for a smoother finish.

Prepare the work area

Sanding can create a lot of dust, so it is crucial to take the necessary precautions. Cover any furniture or items in the room with drop cloths or plastic sheets to protect them from dust. You can also tape the drop cloths to the wall baseboards to ensure that they stay in place. Additionally, it is recommended to wear a dust mask or respirator to avoid inhaling the dust during the sanding process.

Start sanding

Begin sanding the skim coat using gentle, even strokes. Follow the direction of the skim coat application for a more effective sanding process. If you alternated directions with each coat, focus on sanding in the same direction as the final coat application. This will help achieve a smoother finish.

Pay attention to edges and corners

When sanding, pay close attention to the edges and corners of the walls. These areas can be tricky, so take your time and be careful not to apply too much pressure, which could result in sanding through the skim coat or damaging the underlying wall. Use a smaller piece of sandpaper or a sanding block to carefully sand these areas.

Vacuum and wipe down the wall

Once you have finished sanding, thoroughly vacuum the room to remove the dust generated during the process. Use a soft cloth or a slightly damp towel to wipe down the walls, ensuring that all dust is removed. This step is crucial, as any remaining dust can interfere with the painting process and affect the final finish of your walls.

Apply primer and paint

After sanding, you can proceed with priming and painting the walls. The primer will help seal the skim coat and provide a better surface for the paint to adhere to. Follow the manufacturer's instructions for drying times before applying the paint. Typically, you will need to wait until the primer is completely dry before painting.

Frequently asked questions