Proper surface preparation is essential for a successful paint job, and primer is the key to good surface preparation. Using the right type and amount of primer helps ensure a vivid, even color that lasts for years. Exactly how many coats of primer you need depends on what you’re painting, but most paint jobs call for one or two coats.
Why the Right Amount of Primer Matters
Primer is made largely of solvent and resins along with some pigment. The resins seal porous surfaces to create a smoother surface that helps your paint cover more evenly, adhere better, and last longer. It also limits the amount of paint a surface absorbs, protecting the surface and reducing the amount of paint you need for an even finish. Skipping the primer or using too little allows the surface to soak up too much paint, leaving you with dull, blotchy results.
Too much primer causes a different set of problems. Too many layers or an excessively thick layer increases the risk of the primer cracking, crazing, or chipping. It also takes longer to dry, slowing down your redecorating work. In the worst case scenario, it can damage drywall by causing it to bubble and peel.
Applying primer with a standard roller should give you good coverage. If the primer is dripping off your roller as you apply it, you’re using too much. You can expect some of the old base color to show through the dry primer, but the primer will prevent this color from bleeding into your new paint.
It’s equally important to choose the right type of primer for the surface you’re painting and the type of paint you’ll be using. Get it wrong and you might still see stains, marks or prominent color bleeding or blotchiness in your new paint even after applying the recommended amount of primer.
If the surface you’re painting is heavily stained or has been stripped of wallpaper, leaving stain-causing glue behind, a stain-killing primer will give you the best results. Some surfaces, such as masonry and concrete, require a separate sealer to be applied before the primer.
When to Use One Coat
A single coat of primer is all you need if you’re painting over white or very light paint. A painted surface is already prepared to accept another layer of paint, and you won’t have to worry about the light base coat showing through the final coat.
If your old paint color is a medium-light tone, such as sky blue or mint green, and your new color is white or very light, start with a single layer of primer. If the old color shows through after this layer is dry, add a second coat of primer.
Using a tinted primer is another option. By neutralizing the underlying color, tinted primer can cut the amount of primer you need from two layers to one. Factory tinted primer isn’t always easy to find, but most paint stores can tint a primer for you. Adding pigment reduces the primer’s ability to do its job of creating a smooth surface for your new paint, though, so primer should never be tinted more than necessary.
Self-priming paint, as the name implies, doesn’t require a primer, but there’s no harm in using one coat.
When to Use Two Coats
Most unpainted surfaces require two coats of primer. On a surface that’s never been primed or painted, some areas are more porous than others. These areas will absorb paint at different rates, leaving you with a blotchy paint job.
Using two coats of primer solves this problem because the surface will absorb most of the first coat, while the second coat finishes the work by filling in any remaining thin spots.
Wood – For bare wood that’s never been painted, apply two coats of an oil- or water-based primer. Oil-based primers generally perform better on bare wood, but water-based primers can work well on smooth softwood surfaces. For painted wood, use an oil-based primer.
Apply the first coat, then allow 12 to 24 hours of drying time for an oil-based primer or 1 to 2 hours for a water-based primer. When the first coat is dry, apply the second if necessary. A second coat is almost always necessary because wood is highly porous, and few primers contain enough resins to fill the wood’s pores and grain sufficiently with the first coat.
If you choose a water-based primer, lightly sanding the wood after the first coat is dry helps create a smoother surface, but let the primer dry for 24 hours before you do so.
Medium-density fiberboard (MDF) – After sealing the edges, apply two or three coats of an oil-based primer. Avoid water-based primers, which can roughen the fibers in a way that won’t sand out. Because MDF doesn’t absorb primer as quickly as wood, allow at least 24 hours of drying time between coats.
Drywall – Start with one coat of drywall primer-sealer. You’ll get better coverage with a high-build drywall primer, which is thicker than the standard formula. After this layer dries, check for imperfections such as bumps and nicks as well as thin spots. You’ll most likely need a second coat to cover these, but if you’ve used a high-build primer, you might find the wall is smooth enough to paint after one coat.
Plaster – Because plaster is prone to lime stains that can bleed through your final coat of paint, you’ll need an oil-based stain-blocking primer for this surface. Apply one coat, let it dry for 12 to 24 hours, then apply the second coat.
Masonry – Start with one coat of water-based latex primer, let it dry for 1 to 2 hours, then apply another coat if stains still show through. Masonry affected by efflorescence or mildew usually needs two coats. If the wall has prominent stains, use a stain-killing primer.
Concrete – Apply a total of two coats of water-based primer. Acrylic primer is popular for concrete, but polyurethane and epoxy also work well.
Most primers are dry to the touch within a few hours, but for best results, wait at least eight hours before applying your final coat of paint over a water-based primer and 24 hours before painting over an oil-based primer.
With the right type of primer applied in the right amount, you’ll get true, even color that lasts five years or longer. If you’re unsure about how many coats of primer you need for the surface you’re painting, a paint store can advise you. Otherwise, start with one coat and check the surface after it dries. If it still looks rough, porous or heavily colored, apply another coat.