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I was painting my basement and used a six year old five gallon bucket of paint. It had about 4 gallons of paint in it. The surface was black, but it didn't smell bad. I thought it was the dye separating out. It mixed well. I used it on the wall and went to the second bucket for my finish coat. The first bucket was a flat paint and the second an eggshell finish. The second bucket was clear on top before mixing. I now realize the terrible mistake I made. I painted mold onto my walls. I don't know if I am going to have a problem, but my gut feel is not a good one. What can I do to fix this?

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It sounds like you didn't apply the second coat; is that correct? – Niall C. Apr 1 '13 at 21:41
I applied two coats of the flat paint, but none of the eggshell. – MRB Apr 1 '13 at 21:45
Is this a masonry surface or drywall? – HerrBag Apr 2 '13 at 12:18

Mold need two things to create spores, water and air. You probably killed any active mold when you mixed it in the bucket. However, don't fear. Once that coat is dry, recoat with fresh paint. It will seal over the original coat and any surviving mold should be encased and die. I think you will be fine, just repaint.

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Overcoating with a latex paint would be a mistake. Latex is porous and if conditions were right ( high humidity) the mold would have a head start.

I would seal with a shellac primer (BIN comes to mind) or a oil based primer.

Finally, I would add a mildewcide to the eggshell topcoat. There are aftermarket packets that can be added.

I think the best long term insurance is 3 season use of a dehumidifier in this area.

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Could I just wipe the walls down with an water/vinegar mix before painting the topcoat with the added mildewcide? I am wondering if that would kill all the spores in the paint. – MRB Apr 2 '13 at 11:40
The issue is the porosity of (latex) paint and the embedding of the mold. What percentage of removal could you hope to affect? I've not seen vinegar listed as a mold agent. Do you have a source for this? There is a lot of mold info here : epa.gov/mold/index.html – HerrBag Apr 2 '13 at 12:17
If you haven't seen mold growth, and you keep moisture in check (dehumidifier), you are in good shape. Most literature i've seen encourages detergent over bleach for cleaning, emphasizing removing spores over killing them. Your nose will be a good indication that the time for a washdown is at hand. – HerrBag Apr 2 '13 at 12:57
My mistake, I meant to say a cleaning agent such as bleach. I know this would not remove spores, but would it kill them? The more I think about the paint, I am wondering if I jumped to the wrong conclusion. When I opened the can it did not have a spoiled/rancid smell. There was a black layer on the top of the paint, but it had not traveled up the inside of the can. There was a roller left in the paint that I removed and placed in a bag to dry out. A week and a half later, this roller does not smell rancid or show and black growing on it. Should I be able to smell it if it were mold? – MRB Apr 2 '13 at 13:17
I'm not sure the "smell test" is an approved mold detection procedure, or if it's a good idea to go around sniffing mold. – Tester101 Apr 2 '13 at 18:06

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