Black mold patches on wood siding

14 years ago

We purchased an older house that is overall in VERY good shape. However, a sprinkler-placement on the front lawn, plus mold spores in the air, teamed up to turn some areas of the vertical wood siding black. To be more specific, the lower 4-foot portions of about eight boards are stained black. Yet, after a scrupulous inspection, I've determined that all this siding is handsome and sound.

This siding is rough sawn (actually, bandsawed) 11-inch-wide wood boards 7/8" thick - hard to get a replacement for in my area. So because the boards are functionally in good shape and the problem is strictly on the surface, I want to do a cosmetic clean-up.

I remember hearing that household bleach can be used for this purpose. I've also heard that oxalic-acid products can be. (And I remember reading you should never mix these two, since very toxic fumes are yielded.)

I know these chemicals may be used in brand-name products, but the brands may vary with region, so I need to know about what chemicals we're talking about. Are the ones I've mentioned the best products? Anyone know how effective either of them is? Or have another procedure to recommend?

What would be the best thing for me to try on a 'test-patch' area? Thanks.

Comments (10)

graywings123
14 years ago
Buy a box of TSP. There is a recipe on the box for cleaning mildew from decks and siding. It works great. It is something like 1 cup TSP, 3 quarts water, and 1 quart of bleach.

Here is a link that might be useful: TSP
PRO
Christopher Nelson Wallcovering and Painting
14 years ago
Buy a box of TSP. There is a recipe on the box for cleaning mildew from decks and siding. It works great. It is something like 1 cup TSP, 3 quarts water, and 1 quart of bleach.

I would read the directions before applying a QUART od bleach to anything.
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joel_bc
Original Author
14 years ago
graywings, thanks. You say 'It works great' Does this mean you have used it yourself? (sounds like it)

I think I've got a box of TSP in my basement somewhere, so maybe I can find it. Directions should be on the box, eh?
joel_bc
Original Author
14 years ago
Oh, yes... I should ask: I asked this last question because I'm trying to determine how well the TSP/bleach mixture works not only for killing the mold (which I do want to do) but getting rid of the black color.
calliope
14 years ago
Do you think you may be dealing with artillery fungus?
brickeyee
14 years ago
"Do you think you may be dealing with artillery fungus?"

This.
Is there any mulch on the ground under the areas that are blackened?

TSP (you need the real stuff, not a substitute), bleach, and hot water will clean up typical mold and mildew stains.

If you have plants in the area that the mix could drip on, wet them down with water before working in the siding, then rinse them heavily after rinsing the siding.
joel_bc
Original Author
14 years ago
calliope wrote: "Do you think you may be dealing with artillery fungus?"

Haven't been able to do a biological analysis or identification. And I'm living in a remote region, so it's doubtful I could readily find the needed expertise to pin that down.

As far as I can tell (and learn from previous owners of the house), it's a common black mold that has been gradually growing on the surface. The boards are quite sound & solid. So my concern is cosmetic. I'd like to be able to bleach it back to a reasonable "wood tone". Could possibly follow a chemical cleaning/bleaching treatment with a bit of wire brushing using my angle grinder, since the boards have a semi-rough bandsawed texture to begin with.
calliope
14 years ago
Mulch, has there been mulch below the area where you are seeing the black "mold"?
graywings123
14 years ago
graywings, thanks. You say 'It works great' Does this mean you have used it yourself? (sounds like it)

Yes, I have used it. I recently bought a house which was built in 1919 and am using a similar formula on the exterior, since my problem is a combination of dirt and mold. The formula I am using is:
2/3 cup TSP
1/3 cup of laundry detergent (e.g., powdered Tide )
1 quart bleach
3 quarts water

I mix it in a 1 gallon hand pump sprayer and spray on the house and let sit for about 5-10-15 minutes, keeping it moist. Do it in shade. I scrub what I can reach with a brush on the end of a pole and then rinse. I have noticed that it works well on vinyl and metal gutters as well.
Billl
14 years ago
I've used the tsp/bleach/water mix to remove random mold/mildew outside with success as well. I also tried just bleach and water. The bleach and water worked ok in areas that were pretty clean except for the mold. eg a covered porch. However, for the siding and roof, the tsp mixed worked much better.

Also, expect some scrubbing. This is a cleaning product, not a magic wand. I'd start out with a less abrasive brush though, not metal.