Professional painters and home remodelers will definitely recommend that you remove the wallpaper first before painting the walls. However, wallpaper that is firmly adhered to can be difficult to remove. If this is the case, the best option is to paint over the wallpaper. If you have decided to paint the wallpaper, clean the wallpaper first, then apply a primer and sealer. After that you can paint the wallpaper with the paint of your choice.
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Part 1 of 3: Cleaning and Setting Up Wallpaper
Step 1. Practice basic safety
You must come into contact with chemicals when cleaning walls. To protect yourself, wear a mask or ventilator (a device to help breathing), safety glasses, used clothing, and thick gloves. Also open windows and doors so that the room has good ventilation.
Step 2. Clean the entire surface with TSP thoroughly
TSP (short for trisodium phosphate) is a cleaning agent that is able to effectively remove chemicals and oils from the surface of the wallpaper so that the surface becomes clean before applying paint. Mix cup of TSP with 8 liters of water. Use a soft brush or sponge to wipe the walls with the cleaning solution.
You can buy TSP at a paint shop or construction store
Step 3. Allow the TSP to dry
It is important to allow the TSP to dry completely before proceeding to the next step. The drying time will vary depending on the amount of TSP used and the room temperature. It is recommended that you wait at least 24 hours for the TSP to dry completely.
Step 4. Rinse off the wallpaper
When the wall is completely dry, wipe it with a clean damp cloth. Continue wiping until all remaining TSP is gone.
You should use a damp cloth, but not soaking wet. If the cloth is too wet, the walls or wallpaper may be damaged
Step 5. Cover the joint area of the wallpaper with joint compound (a gap filling material made of gypsum)
You do need to cover the joints of the wallpaper so they don't show through the paint (unless this is fine with you). Use a caulk (putty dab) to apply a thin layer of joint compound over the wallpaper joints. Let the coating dry before you sand it.
Joint compound and kape can be found at building and home supply stores
Step 6. Repair the damage with putty and adhesive
You can buy both of these materials at hardware and home supply stores. Check the wallpaper for holes or peeling spots. Cover any holes with putty and apply adhesive to the peeling paper to keep the wallpaper firmly attached.
Use the tools that came with the putty and adhesive product to apply both materials to the wallpaper
Step 7. Sand the area that looks rough
Base paint and wall paint will stick better to the surface that has been sanded. Gently rub the sandpaper over the entire surface of the wallpaper. Pay special attention to areas, such as joints of paper that have been smeared with joint compound, areas that are caulked, and areas of wallpaper that look rough.
Step 8. Remove the remaining dust
After the final sanding, use a cloth to wipe off any remaining dust. Dust and sandpaper can ruin the final appearance of the walls when you paint them.
Part 2 of 3: Applying Primer and Sealer
Step 1. Choose an oil-based primer/sealer mixture
A mixture of primer and sealer can be found at hardware stores. This mixture will prevent the wallpaper from peeling and make it easier for the paint to stick to the walls. When painting on wallpaper, use an oil-based primer/sealer, not water.
Step 2. Apply primer/sealer on the wall
You can use a brush or roller to apply primer/sealer to the wallpaper. Do it the same way you applied the paint, and make sure all nooks, crannies and crevices are covered. One coat of primer/sealer is sufficient.
Step 3. Wait for the wall to dry
You should not paint the walls until the base paint has dried. The drying time will vary depending on the type of primer/sealer used. The approximate drying time will be listed on the can of primer you are using. Some primers/sealers can take a few days to dry.
Part 3 of 3: Applying Paint
Step 1. Apply the tape to the areas you don't want to paint
Protect the baseboard (the board that sits where the wall meets the floor) and window trim using masking tape or duct tape before painting. Make sure everything is covered with tape, as paint can seep and stick to unwanted edges and corners.
Step 2. Use a small brush to reach the corners
Take a small brush (preferably one with angled bristles) to reach hard-to-reach areas first. Target areas such as wall corners, near windows, and along the baseboard.
Step 3. Brush the paint with the letter "M" pattern
Use a roller to apply the paint in an "M" shape. Next, make another "M" overlapping the previous paint stroke. Continue to do this pattern of painting the letter "M" until the entire wall is covered with paint.
Step 4. Wait for the first coat to dry
The paint may take a few days to dry. You should let it dry completely before applying a second coat of paint. The drying time is usually listed on the paint can.
Step 5. Apply an additional coat of paint if necessary
You will usually get better results by applying 2 coats of paint. Apply a second coat if the paint isn't as dark as you'd like, or if there's still some visible part of the wallpaper under the paint.
Step 6. Remove the tape from the wall and check your handiwork
When the paint has dried, remove the tape. If there are still areas that have not been evenly coated with paint, or there are certain areas that have been missed, you can apply paint to those areas specifically.
