Removing Black and Green Mold on Siding & Deck

January 5, 2021 7:13 AM

Our vinyl siding and decks tend to need a good cleaning every few years, we get both black and green mold. Previously I had been doing this myself with a pressure washer I would pre treat the decks with a bleach water mix but use only water on the siding. It was hard work and took me a few days to do it by myself. A couple of years ago I won an exterior house from a Facebook contest from from a local company to clean my siding. The guy walked around the house once with a low pressure hose spraying on some kind of cleaner. Then walked around a second time with a low pressure hose with a water rinse. To me it looked like magic because in the past I was using back breaking brute force to get the mold off. It took this guy less than 20 minutes to do the siding and another 20 or 30 mins to do the deck. House is in need of another cleaning this year and I'd like to do it myself. What was the magical cleaner concoction that he used that only had to sit on the siding for 10 minutes or so before it melted all the mold away and cleaned off with a quick water rinse?
posted by jmsta to Home & Garden (11 answers total)

Very likely it was something similar to the cleaners on this page. These are European products and they work like magic. You will need to wear appropriate protection before using.
posted by einekleine at 7:20 AM on January 5, 2021 [1 favorite]

I don't know what that product would have been, but I've been using a product called "Wet-n-Forget" for years with great success. It doesn't have the quick results, but it contains a long-lasting mildewcide. I retreat it once every 6 months, and live in a perpetually humid environment.

Caution: do not get it on plants. I cover the foundation plantings with plastic before spraying it on and allow the plastic to dry before removing (so, don't do this at 100-degrees in the full sun or you'll cook the plants.)

Initially, after spraying it on, you'll think it doesn't work, but after it dries on, any rain or moisture will activate it. You can hasten this by spraying water on if you'd like, but I never bother.
posted by mightshould at 8:12 AM on January 5, 2021 [2 favorites]

Both einekleine and mightshould's products are very concentrated quaternary ammonium products. While it does eventually break down, it's extremely harmful to nearby aquatic life. It's much in demand right now as it's one of the cleaners that's shown to be effective against COVID-19. It's an irritant and toxic AF above low concentrations, so wear protective gear and keep animals away.
posted by scruss at 8:24 AM on January 5, 2021 [6 favorites]

TSP or borax?
posted by oceano at 10:19 AM on January 5, 2021

I didn't look into how bad it was for my yard and run off, but I poured a combination of warm water and oxyclean on my wood steps outside, and after a few minutes, the gunk and such came off without much work at all, with a regular hose. I don't think I even scrubbed very much. I got some proper mold cleaner for next time. All of this is to say... maybe take a look at oxyclean if these other options aren't available.
posted by bluedaisy at 10:55 AM on January 5, 2021

Best answer: The aforementioned Wet n Forget is what I’ve always heard is best for this kind of thing, but I know you can’t buy it in (or have it shipped to) California (which tends to be strict about environmental matters; make of that what you will).
posted by lovableiago at 11:34 AM on January 5, 2021

Best answer: It could have been 30 Second Outdoor Cleaner. We used it on a north-facing outside wall that gets pretty gross and it seriously worked like magic right before our eyes. We got it at one of the big-box stores (HD or Lowe's, can't recall which). It says not to use it in a pressure washer but we used one anyway basically to spray it at low-pressure on the complete 2-story wall. Wear goggles; it's basically very strong bleach-type stuff.
posted by jquinby at 12:16 PM on January 5, 2021

Can you apply a sealant to the vinyl AFTER you de-mold it?
posted by kschang at 12:39 PM on January 5, 2021 [1 favorite]

I have used Stain Solver to clean both decks and vinyl siding. Mix in a bucket with hot water and apply with a brush, let sit for 15 to 20 minutes, light scrubbing and then rinse. Worked great. The nice thing about Stain Solver is that it is environment friendly and has many other uses around the house.
posted by tman99 at 1:10 PM on January 5, 2021 [1 favorite]

Seconding @jquinby on 30 Seconds cleaner. It's what we use for our complex, and it works like magic.
posted by tamarack at 10:49 PM on January 5, 2021

I didn't look into how bad it was for my yard and run off, but I poured a combination of warm water and oxyclean on my wood steps outside, and after a few minutes, the gunk and such came off without much work at all, with a regular hose. I don't think I even scrubbed very much.

Oxygen cleaners can be a relatively safe cleaner for this sort of thing. OxoBrite Free and Clear probably better than Oxyclean, which is full of additives.
posted by oneirodynia at 7:19 PM on January 7, 2021 [1 favorite]