How to deal with wall covering wallpaper

It's advisable not to paint over new walls before applying wallpaper. For new houses, the substrate preparation is relatively simple. The process is similar to traditional wall construction, but instead of painting, you apply an interface agent on the plaster layer, followed by two to three coats of putty. Once this is done, you can proceed with other renovations like tiling or painting, and finally install the wallpaper when everything is complete.

If you're working with an old house that has painted walls, it's important to test the existing paint first. Can you directly apply wallpaper over the old paint? This depends on the condition of the original surface. If the paint is firmly attached and hasn't peeled off, you can apply a base film (a key material for wallpaper installation) to strengthen the wall, improve adhesion, and protect the surface when removing the wallpaper later. However, if the paint is loose or flaking, you may need to remove the old substrate entirely.

How can you tell if the old paint needs to be removed? You can do a simple self-test. Take a damp cloth (not dripping) and press it against the wall for a few hours. Check the next day—if the paint remains intact and doesn’t peel, the wall is in good condition and ready for the base film and wallpaper. But if the paint starts peeling or blistering, it’s a sign of instability. Applying wallpaper directly in such cases could lead to poor adhesion and future peeling.

If the entire wall is unstable, you'll need to remove all the old paint and plaster, reapply the interface agent, and then sand and apply putty again. If only part of the wall is problematic, just remove that section, reapply the interface agent, and use a wallpaper knife to score the surface in a crosshatch pattern. The deeper the scratches, the better—this helps the new putty adhere more securely. This step ensures a stable base, reducing the risk of cracks or peeling in the long run.