Declan's paint course: Is the wall painted or not? Wall pain is never oil based if painted, oil or water? Oil paint for wood, (only really applies to wood) What material is the paint being applied to? What environment will the paint be subject to? 1. Paint a door 2. Sugar soap 3. Sandpaper 120 grit. Giving it a key (Keying it) 4. Prime it, paint attaches to primer, primer attaches to wood. Paint does not apply to the wood 5. Paint it. Water paint you need to paint several layers Oil paints start to appear yellow, this applies to all of them. The time it starts turning yellow depends on the ingredients and the environment the paint is subject to, but the yellowing of the paint is guaranteed to happen. This is due to the oil in the paint rising to the surface.