
Skim coating over wallpaper glue is possible, but it requires several steps and special tools. Firstly, you need to scrape off any remaining wallpaper scraps using a razor knife and a taping knife. Then, you must remove the adhesive by sealing it with an oil-based primer or surface sealer. Once the primer is dry, you can apply a joint compound or drywall mud with a taping knife or paint roller. Finally, you can make repairs by taping over any remaining tape marks with matte fiberglass tape and applying a thin layer of the joint compound.
What You'll Learn
Seal the glue with an oil-based primer
Sealing wallpaper glue with an oil-based primer is an important step before skim coating, as it prevents the glue from reactivating and creating a clumpy or wavy texture. It also ensures that the paint adheres properly to the wall and doesn't crack or chip prematurely.
To seal the glue with an oil-based primer, start by lightly sanding the wallpaper glue with #220-grit sandpaper to level any high spots. Be careful not to sand too aggressively, as you can damage the underlying drywall paper. Use a brush attachment on a shop vacuum to remove the sanding debris, avoiding the use of water.
Once the surface is prepared, it's time to apply the oil-based primer. This step is crucial in creating an impermeable barrier between the water-soluble wallpaper paste and the water-rich latex paint you'll use for skim coating. Take your time to apply a thin and even coat of the primer to the entire wall, paying extra attention to the corners to ensure complete coverage. Allow the primer to dry thoroughly before proceeding, which typically takes between eight to 24 hours. The longer you can let it dry, the better.
Oil-based primers are effective in sealing the adhesives on the wall. However, it's important to note that water-based primers will not have the same sealing effect on glue. This step may be time-consuming, but it is essential to ensure the success of your skim coating project.
After the primer has dried completely, you can move on to the next step of skim coating, which involves applying a thin layer of drywall joint compound or "mud" with a drywall knife or paint roller. This process will help you achieve a smooth and even surface, ready for painting.
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Scrape off remaining wallpaper
Before skim coating over wallpaper glue, you must first remove the wallpaper. This can be done in several ways, depending on the type of wallpaper you are dealing with.
If you are dealing with strippable wallpaper, simply use a putty knife to lift the corner of the paper and then use your hands to peel the paper from the wall, pulling as close to the wall as possible to avoid tearing the paper. If the paper does rip, loosen another corner and start again.
For traditional wallpaper, you will need to apply a hot water solution to the paper and adhesive backing to reactivate the adhesive and allow the paper to come off the wall. You can make this solution by mixing hot water with either fabric softener or vinegar. Use a spray bottle, garden sprayer, or paint roller to apply the solution to a small section of the wall, wait several minutes, and then use a putty knife or scraper to peel off the wallpaper, working your way up the wall. Be careful not to gouge the drywall as you scrape.
If you are dealing with peelable wallpaper, you can remove the top layer by loosening the corner with a putty knife and pulling the paper off the paper backing. To remove the paper backing, use the same method described above for traditional wallpaper.
If the wallpaper is being particularly stubborn, you may need to use a wallpaper steamer. Follow the manufacturer's directions to prepare the steamer, being sure to wear protective gloves and long sleeves to avoid burns. Hold the steamer to the wallpaper to loosen the adhesive, and scrape the wallpaper off with a putty knife. If the steam isn't penetrating the wallpaper, use a scoring tool to make small holes in the paper.
Once all the wallpaper has been removed, you will likely still have some residual wallpaper adhesive on the wall. This can be removed by lightly steaming one area of the wall at a time and using a putty knife to scrape off the excess glue, followed by scrubbing the rest off with a damp sponge and warm water.
It is important to note that wallpaper glue is tricky, and even when it seems like you've removed it all, there may still be residual glue that can reactivate when you paint the walls, causing your paint job to be compromised. To prevent this, lightly sand the walls and then apply a coat of a problem surface sealer like Zinsser ALLPRIME Water-Base Problem Surface Sealer or Gardz Problem Surface Sealer.
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Remove the adhesive
Removing wallpaper glue can be a tedious task. Here are some tips to help you get rid of the adhesive residue:
Wash the glue off
Create a solution of hot water, liquid dish soap, and a tablespoon of baking soda in a bucket. You can also add vinegar to this mixture if the glue is stubborn. Wearing gloves, soak a sponge in the solution, wring it out, and gently rub it onto the wall. Work in small sections, lightly rubbing the wall to remove the glue residue. Rinse the soap from the walls and dry the surface with a clean cloth or towel.
Scrape away the glue
Use a putty knife or a drywall knife to scrape away any remaining glue after washing. Hold the knife as flat as possible to avoid gouging the surface. Work quickly to prevent the glue from drying again.
Sand the walls
If the glue is still not coming off, let the walls dry completely. Then, use #220-grit sandpaper on an electric oscillating sander to sand the walls gently. Avoid pressing too hard on the sander, and follow each pass with your hand to check for smoothness.
Prime the walls
Once the walls are smooth and free of glue, apply a primer to seal the surface and prepare it for skim coating. An oil-based primer is recommended to separate the water-soluble wallpaper paste from the water-based paint. Let the primer dry completely before proceeding.
Skim coat
Apply a thin layer of drywall joint compound using a drywall knife or paint roller. A drywall knife will help you achieve a smoother finish. Sand the skim coat once it's dry to create a smooth wall surface.
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Apply a joint compound
Now that you're done sealing the glue, you can start skim coating the wall. For this, you'll need a taping knife (6 inches) and joint compound (preferably drywall mud). Take your taping knife and start applying the joint compound generously over the walls, paying special attention to the corners.
There are many types of joint compounds available, so it's important to choose the best kind. We recommend drywall mud as it is the most suitable joint compound for skim coating. Apply a layer of joint compound generously over the walls, again being careful to pay attention to the corners.
If you notice any tape marks left on the wall from the previous wallpaper, you can use matte fiberglass tape to cover them up. Apply the tape over the marks and then add a thin layer of the joint compound on top. This will ensure that your wall looks as good as new.
Once you're done applying the joint compound, you can move on to the next step of the process, which is sanding the skim coat.
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Make repairs by taping
Before you start skim coating, it is important to repair any damage to the drywall. This includes filling in any holes, cracks, or gaps with a setting-type joint compound. Let the compound harden before proceeding to the next step.
Once the compound is dry, it's time to tape the seams and cover them with joint compound. Choose a high-quality joint compound suitable for your project and mix it to a creamy, pudding-like consistency. You can use a hawk and trowel for this step if you're experienced, but a paint roller and a squeegee knife can also get the job done.
Start by rolling a fast-drying, stain-sealing drywall primer onto the walls. This will seal loose paper and improve adhesion. Then, spread a thin layer of slightly thinned all-purpose joint compound onto the walls using a heavy-nap roller. Work in small sections and smooth out the compound with a squeegee knife before it dries.
Use a 1/2-inch nap roller to apply mud to an area of about four feet square. Try to keep the layer as even as possible for better squeegee work. Use the squeegee knife to smooth out the joint compound, pulling it down in vertical passes and overlapping each pass until you finish the section.
If you notice any cracking on the first coat, simply mix the next coat a little thicker by adding some fresh mud. You may need to go over some areas multiple times to achieve a smooth finish. Once you're done with the top section, move on to the lower half, rolling joint compound and smoothing it by pulling the trowel upward.
Let the first coat of joint compound dry completely before moving on to the next step. You can speed up the drying time by using a space heater and a box fan, especially in humid conditions.
Before applying the next coat, knock off any lumps or proud mud lines with a putty knife to avoid streaks. Brush off the wall, and you're ready for the second coat. Remember to change directions with each successive layer, trowelling at a right angle to the previous one.
If you still see imperfections after the second coat dries, apply a third coat as needed. After the final coat dries, sand the wall with 120-grit paper for a smooth finish. If there are significant peaks and valleys, start with 100-grit sandpaper first.
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Frequently asked questions
Yes, but you need to seal the glue first. You can do this by applying an oil-based primer.
You will need a drywall taping knife, an oil-based primer, matte fiberglass tape, and a joint compound (preferably drywall mud).
First, scrape off any remaining scraps of wallpaper. Then, apply a thin coat of oil-based primer to the wall and let it dry. Next, apply a layer of joint compound generously over the walls, especially in the corners. Finally, if there are any tape marks left from the wallpaper, cover them with matte fiberglass tape and apply a thin layer of joint compound on top.
Fill a spray bottle with water and spray it onto the wall. Wait around 5-6 minutes, then run your hand across the damp areas. If the areas feel dry and not sticky, the glue is gone.
Sanding the walls is not mandatory, but if your wall is damaged and not smooth, you can spray water across the wall and sand it quickly before the water dries.