SMOKINCHOICES (and other musings)

July 30, 2013

Can remove Stucco stains

Black stains on stucco removable

Ask the Builder

Tim Carter

Q: My house was built in 1985, and I have never painted the stucco. I plan to do it this year. Other houses in the neighborhood have a black bleed coming through the stucco. Should I use a special type of paint or prepare the surface?

  • A: I’m going to do my best to talk you out of painting your stucco. You’d be transforming a maintenance-free surface to one that requires upkeep.

Bushes and trees growing near a stucco wall could fuel mold and mildew from aerosol sugars being emitted from the leaves. Shade creates a breeding ground for mold because it raises the humidity level. Mold and mildew need water to flourish.

The black stains you see could be an accumulation of the dead, dark-colored cells of the hardy algae Gloeocapsa magma, which feeds on the calcium carbonate in the unpainted stucco mixture.

But it’s easy to remove the black stains — whether they’re mold, mildew or algae — with oxygen bleach. (Do not use chlorine bleach, which will kill the bushes and trees next to your home.)

Dissolve the oxygen bleach powder in water and put it in a hand-pump garden sprayer. Saturate the stucco and keep it wet with the solution for up to 30 minutes. Use a stiff scrub brush dipped in the solution to remove the black stains. Adding regular liquid dish soap helps the cleaning. Rinse immediately with clear water from a garden hose.

To keep the stucco free of mold, mildew and algae, periodically clean it with liquid dish soap and water. If the stains are caused by mold and mildew, this removes the invisible food they’re feasting on.

  • If the stains are the black algae, you have to introduce copper, a natural biocide that inhibits the growth of mold, mildew and the algae. You can attach small copper strips to the upper parts of the walls or put the strips under the last row of shingles. Then, each time it rains, a miniscule amount of copper washes down the walls, keeping the stucco looking fantastic.

Tim Carter is a columnist for Tribune Media Services. He can be reached via his website,

(This post of course is not for your body’s health either – tho it could be, – – but rather, the health and well-being of your house. And it sounds to me like you’d save a lot of money and time and effort if you take Tim’s advice.   Just sayin’ . . .   .  Jan))

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