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Ask the Carpenter: Getting mold off cedar shingles, paint off brick

Ask the Expert Home Improvement
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Q. The cedar shingles on all sides of our house have mold. My husband has used a power washer on the house over the years. Does that spread mold? How can we get this under control? We have also been told that we have too much insulation in the attic and plan to take some out. What do you suggest? Thank you.

ROSEMARIE DEBENEDETTO, Reading

A. Mold and algae grow on wood surfaces over time. This is normal, and these organisms do not break down the structural components of wood.

Evidence does suggests that a pressure washer can spread mold if you don’t take the steps to kill it first.

My painting contractors all recommend using commercial cleaners containing sodium percarbonate or other oxygen bleaches because they are gentler on wood than chlorine bleach. Chlorine bleaches tend to cause excessive pulping of the wood, giving it a fuzzy surface. For wood shingles, you’ll want an antimicrobial cleaning product.

NOTE: Some cleaners contain strong concentrations of sodium hydroxide or potassium hydroxide, which can accelerate paint removal. You also want to protect your plants and lawn before applying any cleaner.

It’s best to wet the surface, and then apply your cleaning solutions with a garden-type sprayer or a soft-bristle brush dipped in a bucket of solution. Keep the surface wet, making sure you allow the solution at least 15 minutes to do its job.

CLEANING TIP: Some of my painters swear that adding a few drops of dishwashing soap helps the cleaner stick to the wood siding. The dish soap acts as a surfactant, meaning it lowers the surface tension of the liquid in which it’s dissolved, allowing the cleaning solution to penetrate porous surfaces.

Rinse with a garden hose, keeping the stream pointed down. I start at the top and clean downward to avoid streaking. You do not need a pressure washer.

 

Q. I have an L-shaped ranch on a slab. The home is 60 years old and has a wood shake and red-brick facade. Over the years I have painted the shakes many times and have splashed paint on the brick. How do I remove the spots before I sell my home? Are there products I can get from the hardware store that will work?

DONALD MINER, Framingham

A. I spoke to Dan Frost of H.D.F. Painting, and he said it is difficult to remove paint from brick. If the paint is latex, you can try spraying the spots with Krud Kutter. Soak the spots well, let the product sit for five minutes, and then power-wash it off. Gently scrubbing with a wire brush may also help.

If the paint is oil, use 5F5 paint stripper and then power-wash. It may take a few applications and discolor the surface, creating a “cleaned’’ area.

Your last option is to paint the brick. I’m not a fan of that.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.