Mold on exterior primer

[tweaked]

I primed some hardiboard last fall and let it go through the winter. There is some signs of mold. What is best procedure before priming and painting?

Thanks

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[m Ransley]

Use bleach to kill it maybe a 25% mix in water, you probably need to reprime , many primers give 6 mo open time

[Joe Bobst]

How do you know its mold and not just common dirt, grunge, urban smog deposits, or some such?

Celebrate! Now you've got an excuse to buy the hottest yuppie toy, a power washer.

But, if you have proven that it is in fact a mold growth, there are the usual remedies mentioned exhaustively in this newsgroup. For different approach I would clean it (scrub brush, power washer, whatever) and, if the area wasn't obscenely large, use a heat gun to thoroughly dry it, then continue the heat application to a fairly high surface temperature, say 270 F (which ought to kill mold spores dead as Hades), and as soon as it cooled to ambient, slap on a coat of primer, maybe with a mildewcide added. Meanwhile, discussing the problem with the hardiboard customer service people might elicit some helpful information. Perhaps the paint folks, too. Good luck.

Joe

[m Ransley]

Heat to 270 ? bubble the primer and ruin it more likely.