LESLIE: Alright, next up we’ve got Rick in Delaware who’s dealing with some stains on the roof. Tell us about them.
RICK: I was told they’re algae stains or black stains; the little stains that you see on rooftops.
RICK: Yeah. I’ve got some information; different ways to get rid of it.
RICK: I wanted your opinion.
RICK: I was told zinc – some kind of zinc strips or copper strips. Would that be right?
TOM: Yep. Mm-hmm, that’s correct. But that’s only part of the solution. What you want to do first is you want to treat it with a mildicide. You can get a commercially-available mildicide at any home improvement store or hardware store; sometimes they’re sold as siding wash or deck wash. And that’s going to treat the plant growth itself that’s causing this.
You apply the mildicide, let it soak for a little bit; maybe get up there with a broom if you can walk on it and abrade it. Rinse it off and, after the roof is clean, then you can add zinc strips or copper strips; perhaps across the ridge vent. And the reason you’re putting that there is because as the rain water hits it, it releases some zinc, it releases some copper into the rainwater; it washes down the roof and that acts as a mildicide as well and keeps it clean for the long run.
That’s why sometimes when you look up at a roof that has a chimney and, say, copper flashing or zinc flashing, you’ll see like white streaks under it. That’s the effect of the water hitting the flashing and washing down over that roof. It’ll clean that spot.
RICK: Oh, I see. Yeah, you’re right because I do have copper around my chimney.
TOM: Yep, and that’s what’s going on.
RICK: OK. Thank you.
TOM: You’re welcome. Thanks so much for calling us at 1-888-MONEY-PIT.