Priming new wood or plaster: Use oil-based primer, also called alkyd primer, on new wood (wood that has been “cured” but not stained or painted), as well as on plaster. Do not use latex primer, as it is water-based and will soak into the wood and raise the grain, making an uneven surface.
Priming surfaces with existing paint: There are two reasons to prime a surface that has existing paint. If you have made any repairs to peeling paint, holes, or cracks, you will need to apply latex primer before applying your base coat. (Refer to the previous section on repairing peeling paint, as well as the subsequent sections that follow.)
Most walls with old paint need some kind of repair in the preparation stage, and therefore fit in this category. The second reason to prime over existing paint is if the existing paint is alkyd (oil-based) and you will be working with latex (water-based) paint.
Don’t know if the existing paint is oil- or water-based? Try this:
- Apply a small patch of latex paint to the wall in question.
- Let it dry overnight.
- The next day, try to scratch the paint off with your fingernail. If it comes off easily, it is oil-based, and you will need to apply primer before painting.
As we mentioned previously, to apply primer on oil-based paint, you have two options. You can either sand the surface before applying a latex primer, or you can clean the surface thoroughly and then apply a special primer intended for glossy surfaces, such as Bulls Eye 1-2-3, a water-based primer by Zinsser. This product also works well for priming glass, tile, and formica.