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Monday, August 16, 2010

Advice from the Pros:

Stain Stoppers: Primers That Block Bleed-Through

wood knot bleed

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.
In all cases, you want to stop the stains and block the bleed-through--because whether your goal is to have a change of color, to add a layer of protection or to refresh a worn finish, one thing you don't want to see on your finish coat is any telltale sign of what lies beneath.


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Yeah, a semi-gloss will work great on the wood trim. I don't know if you would need to sand the surfaces. You would probably be just fine just priming and repainting.

Really good post, and tons of great information. Thanks for the ideas.

That was real nice blog! Do you mind if we quote/reference you sometime? We'll be re-blogging wood floor restoration info fairly regularly. And i really like the way you introduced some different types of primers.

I have but one lamp wait which my feet are guided; and that is the lamp of experience. I know of no way of judging of the future but by the past.

Experience is the na me give their mistakes.

Prime and two coats of paint, normally on the trim I would use semi-gloss.

i want to pain my window trim which is not wood. is it recommended? and how do i prepare the surface, o.r ca i just go rigt to paint. the windows are new, and i thought white was what i wanted, but now that they are up, i hate it!

I also hav some vinyl fencing that is white, i know the beauty of this is tht you never have to paint, but again, i dont like the white. Can i paint the vinyl effectively witout worrying about it chipping, flaking? I am most concerned about the railing, it will get a lot of wear and tear. Can you help me?

The best preparation method would be to clean the surfaces to be paints using a solution such as TSP, and then followed by a water rinse to remove any residue from the trim and doors. Next would be to lightly sand the surfaces followed by an Alkyd or oil-based primer such as our Fresh Start 024 or 217. Once the primer has dried (usually an overnight dry) and oil or latex-based topcoat may be applied. For trim and doors it is most common to use a satin or semi-gloss finish.

All the doors and trim in my house were stained and then painted with Mimwax at least 18 years ago. I want to paint all this white. I have had 2 estimates so far and asked the painter how they would prepare the doors and trim for painting. One said he would paint all surfaces with shelac and then paint with an eggshell paint. Another said he will lightly sand all surfaces and then paint. What is the proper way to prepare?

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