Ask TOH Stained Stucco
The mildew stains under the eaves of this Rochester, N.Y. house should disappear after applying a bleach-activated house cleaner.
Q: We own a magnificent 1926 Tudor-style home, which we've been renovating for two years. But there's one nagging problem we can't seem to solve: The unpainted stucco exterior is stained in many areas, and a pressure-washing with a house cleaner hasn't helped. We're reluctant to paint (we don't want the extra maintenance), and even if we did, we'd have to remove the stains anyway. What do you suggest we do?

— Donna, New York

A: Jim says: Judging by the color and location of the staining, I'd bet that you're battling mildew, which is particularly common under eaves. Pressure-washing with a house cleaner generally removes it, so I'd guess you either used an ineffective cleaner or didn't use it properly.

When we clean stucco, or other kinds of sidings for that matter, we use a concentrated cleaner designed for exterior use only, such as Jomax, and activate it with household bleach. After spraying any nearby plants with water to protect them from the chemicals, I mix the cleaner with bleach (following the directions on the cleaner bottle) and squirt the solution on the walls using a simple pump sprayer. After the stuff has been on for a few minutes, I gently rinse it off with a pressure washer, starting at the top of the wall and working down. Don't blast away with an aggressive nozzle or you could end up damaging the stucco surface.

Although I'm in the business of painting houses, I share your reluctance about painting stucco; you'll have less maintenance and expense in the long run if you leave it "raw" and wash it regularly. (Jim Clark, a painting contractor in Sudbury, Massachusetts, painted the last two This Old House projects.)
Ask TOH users about Cleaning

Contribute to This Story Below