Primers and sealers provide an extra measure of assurance that the paint you use will adhere to its surface. In effect, primers and sealers are preparatory products that give the surface tooth that the paint can grip. Because of their importance, there are aisles dedicated to primer and sealers at the hardware store. To figure out what you're looking for, check out our guide to paint primers and sealers. We'll help you get the job done right, the first time.
Primers are formulated to adhere to the substrate and create a uniform surface for the finish coat. Primers stick to the surface; finish coats stick to the primer. Primers penetrate unpainted surfaces, smoothing out any porosity. Primers for wood, whether they are latex or oil-base, contain specialized ingredients that topcoats don't necessarily have, or have in lesser amounts. Stain-inhibiting tannin blockers or preservatives that are found in primers, for instance, are designed to soak into raw wood and seal it so the tannins don't bleed through and stain the finish paint. Primers for other surfaces have similarly specialized ingredients. Latex primers are best for unfinished drywall.
On raw interior wood, oil-base primers may be a better choice because of their surface penetration. On the exterior, a latex primer will last longer because it's more flexible, expanding and contracting with changes in temperature instead of cracking. There are a number of different kinds of primers—oil-base, shellac-base, water-base—and each has its own specialty. Ask your retailer for a recommendation on which product to use on the surface you're painting.
Many homeowners, in a rush to complete a project, skip the primer and go right to the color coats. This shortcut often backfires because it may take an extra coat of color to get complete coverage. Because primer is cheaper than paint, that represents both wasted time and money.
Primer is specially formulated to bond to raw wood and to seal porous surfaces such as drywall. Drywall and drywall joint compound soak up paint fast, and if you've invested in a high-quality paint, you want your investment on the wall, not in it. Prime all drywall joint compound and let the primer dry. Then prime the entire surface of the wall.
Primer typically dries rapidly so you apply the finish coat sooner. So a good primer saves time, effort, and money. Consider tinting your primer to the color of your paint so the paint covers better. Your paint retailer can tint the primer.
Sealers, closely related to primers, are formulated to make a porous surface non-porous. They are also used to cover knots and mildew to keep them from showing through the finish coats. You'll find oil-base sealers, as well as products with reactive resins and epoxies. Most of these products clean up with strong petroleum solvents.
Primers and sealers come in an array of formulations. It's important to choose the right one for your job.
Most interior primers are designed for specific applications and come in both latex and oil-base formulations. You may prefer latex products because the reduced odors are an advantage when working indoors.