Q. October 22, 2011. I have a question regarding mold on the exterior wood siding on my house.  I own a 1950's rambler style home in Minnesota and in a few areas I am seeing a black mold on the exterior siding.  It of course tends to be in areas under the eaves where the sun is not on the house.  We also live across the street from a wetland area but we are set up on a hill from there.  What can I use to remove the mold before I want to repaint the house?  Also, are there things I can do to help keep it from coming back.  The worst area on the house is the east side and this happens to be the wall of two bedrooms.  Could that mold being outdoors still effect my health?  We have not seen any trace or signs of mold in the interior of the house. Please let me know what you would recommend.

A. You  are smart to worry about the siding mold growth, especially since airborne mold spores from the mold growth can travel in the air to enter nearby bedroom windows.  The most effective and safest (non-toxic to use) mold remover product is boric acid powder mixed with hydrogen peroxide in the mix formula explained in the boric powder page on Mold Mart http://www.moldmart.net, wherein you can also buy five to ten pounds of boric acid to carry out the mold remediation of your moldy wood siding. Use a hand-pumped garden sprayer (low cost from a hardware store or home improvement center) to spray the boric-hydrogen peroxide mix onto the moldy areas plus two feet beyond in all directions from the mold growth.  Let the spray work on the siding for about one hour (or earlier if dried). Then, use a hand-held wire brush and hard bristle brush (both of which you should keep continually dripping-wet with lots of boric-hydrogen peroxide mix) to remove the mold growth physically until you get to clean, no visible mold-growth wood. When you repaint the dried and cleaned siding surface, use paint into which you have thoroughly mixed two cups of boric acid powder (not mixed with hydrogen peroxide) per gallon of paint. The boric crystals will be an excellent mold preventative.  The siding mold grows because it has paint and wood to eat, but also because airborne mold spores and organic dirt settle on the surface of the siding to enable mold to grow thereon.  At least every two or three months, you should use a high pressure sprayer to power wash accumulated surface dirt and mold spores off of all of the siding on that section of your exterior house wall. You would also be helped if you read two my mold advice ebooks Mold Health Guide and Do It Best Yourself Mold Inspection, Testing, Remediation, and Prevention, only $15 each for email attachment delivery to you from Mold Mart. If I can be of further help, please email me. Thanks, Phillip Fry, Certified Environmental Hygienist, Certified Mold Inspector, and Certified Mold Remediator