What’s On My Walls?
Before applying new paint to your home’s interior surfaces, it’s important to know what type of finish is currently on them. Here’s how to find out: Put a little denatured alcohol — the kind you can buy at hardware stores — on a white piece of fabric (rag, cloth, or T-shirt). Apply the alcohol to a section of the finish you want to evaluate. It will remove acrylic/latex paint; alkyd paint, on the other hand, will remain on the wall.
Why Does It Matter?
If you want to cover a wall with acrylic paint, and it was last painted with alkyd, you’ll need to apply primer first. Specifically, you’ll need to use a primer that can stick to oil-based paint while allowing acrylic to stick to the primer.
In contrast, you can brush or roll alkyd paint over acrylic without priming. If the new paint is oil based, the nature of the old paint doesn’t matter. All you need to do is wash the walls and fix any surface irregularities. In sum, the purpose of testing the paint on your walls before adding more is to determine whether priming is necessary.