Stain Stoppers: Primers That Block Bleed-Through
Stains or bleed-through present special challenges and often call for special primers and/or specialty sealers. An effective blocking product depends upon the problem stain and on the finish material. But with all of the possible stain offenders (wood knots, smoke, soot, ink, crayon, lipstick, tannins, oils, watermarks, rust, etc.) and the vast varieties of primers, what's a painter to do? Here are a few guidelines on how to choose the right primer/sealer to stop the problem stain:
- First, is there a difference between a primer and a sealer? Yes, a primer provides a foundation for adhesion and coverage of the finish material, while sealers are formulated to suppress stains.
- What is an underbody? An underbody is an alkyd or acrylic primer that is heavier-bodied, allowing you to sand it to a smooth finish before applying an enamel paint (typically on wood). Its perm rating (less than 1) means that a film of Alkyd Enamel Underbody not only blocks stains, it also acts as a vapor barrier.
- Which is best: acrylic primers or alkyd? That depends. If the offending stain is an oil-base substance (such as crayon, soot or a build-up of skin oils), a water-base (acrylic) primer is less tolerant. Spot-prime these bleed-through problems with oil (alkyd) sealers. A solvent-thinned primer, such as Benjamin Moore 024 Fresh Start All Purpose Primer suppresses wood knots, smoke stains, and water marks for interior applications.
- Are fast-drying primers best? Fast drying primers have the advantage of being ready to topcoat soon but will become brittle. But slow-drying (alkyd) primers penetrate better into the substrate, and they remain more flexible, offering better penetration and adhesion.