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Tough Wall Stain: How to Seal in With Primer

  • Transcript

    LESLIE: Tim in Iowa is dealing with a mysterious stain on the wall. Tell us about it.

    TIM: Well, I got an old 1920-built house with plaster walls. I got dark – I got, in one area where there used to a window at one time, I’m guessing, I got some dark spots bleeding through.

    TOM: OK. And do you think that there’s any moisture behind those spots or is it really just a condition of the paint finish that’s bothering you?

    TIM: I think it’s the paint finish. Actually, the other side of the wall used to be exposed to the outside with a front porch but about five, six years ago I finished off the front porch, so it’s not an exterior wall anymore.

    TOM: OK.

    TIM: I actually took a hole saw and bored through one of the dark spots or two of the dark spots and I don’t see …

    TOM: You did a little surgery there, huh?

    TIM: Yeah, well that was my first thing because I thought, “Oh, my gosh. Maybe I’ve got mold in the wall.”

    TOM: Yeah.

    TIM: But went in there with a bore scope and I don’t see any mold in the wall.

    TOM: Yeah.

    TIM: And actually, to me, the plaster doesn’t even look discolored. To me, it almost looks like it’s maybe how many years ago some …

    TOM: Sure.

    TIM: You know, some odd, lead-based paint or something that had something in it. You know, I don’t know. But it almost seems to be in the corners where this window used to be, so …

    TOM: Right. Well, what happens is if you get a stain in the wall, that will leach through successive coats of paint. The only way to stop it is by using a good-quality primer and in this case we would recommend that you only use an oil-based primer because the oil-based primer will effectively seal in what’s there and give you a neutral surface to go on top of.

    What people don’t understand is that the qualities of a primer and the qualities of paint are quite different. Primer is kind of like the glue that makes the paint stick; and so whenever you have a questionable surface like that, if you hit the whole thing – and you can’t spot-prime this because, if you do, you’re going to get sort of an uneven finish when you put the top-coat on; but you want to prime the entire wall surface with an oil-based primer and that will absolutely seal in whatever is there and then you could put wall paint on top of that. I would try to stay within the same manufacturer family but make sure it’s oil-based. It’ll do a much better job than a water-based or an acrylic-based primer.

    TIM: Alright, thank you very much.

    TOM: You’re welcome. Thanks so much for calling us at 1-888-MONEY-PIT.

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