Types of Primers
Primers are available in oil, shellac, or latex-based formulas. Each type has differing properties and uses a different solvent for thinning and cleanup. Choosing which type to use is largely a matter of matching the primer’s characteristics to the project at hand.
When to Prime
Every unfinished surface—including wood, drywall, metal, and concrete—should be primed before painting. While it can be tempting to skip this step, the results are almost always disappointing. Paint applied to unprimed surfaces tends to peel, crack, and chalk more than paint applied to properly primed surfaces.
Previously painted surfaces may not require priming unless you’re switching between oil-based or latex paint, or the existing paint is failing. Always scrape and sand any deteriorating surfaces before applying primer. Remember, your paint job is no better than the preparation that goes into it.
Good to use for:
Shellac primers should be used to prime or spot prime:
Latex primers are not as brittle as their oil or shellac-based cousins and provide a more flexible finish that is resistant to cracking. This makes them suitable for priming bare softwoods, though test them first to see if they raise the grain or allow resin to bleed through.
Latex primers are the best choice for unfinished drywall, since they act to even out the texture and sheen between the wallboard and joint compound. They also allow water vapor to pass through, which can make them less likely to peel.
Use latex primers on:
Oil/Latex Paint Test
If you’re not sure whether the existing paint is oil-based or latex, wipe a small area with a clean rag saturated with denatured alcohol, paint de-glosser, or non-acetone fingernail polish remover. If the paint is oil-based, it won’t be affected. If it’s latex, some paint will come off on the rag or the surface will become tacky.