How do I clean mold and scum off brick and concrete?

October 17, 2016 10:59 AM

I have a concrete carport with a brick trim, and it doesn’t drain well and sometimes has leaves on it, meaning there’s a decent build-up of green mold and some black stuff that’s probably mold or some other fungus. What’s a good cleaner or other stuff to use to eliminate it, without a ton of scrubbing or causing some kind of major environmental damage to my yard?
posted by ivey to Home & Garden (8 answers total)

My first try would be a pressure washer with plain water (don't hold it so close enough you remove mortar). If that doesn't work, I'd try the same with detergent.
posted by ssg at 11:00 AM on October 17, 2016 [5 favorites]

Vinegar kills many kinds of mold and is not environmentally horrible. It won't work without scrubbing (or a pressure washer) though.
Pressure washer with a vinegar-water mix could totally work.
posted by Too-Ticky at 11:07 AM on October 17, 2016 [2 favorites]

I would pressure-wash first and then (if you must) apply a mold-mildew treatment afterwards so you're not aerosolizing anything more into the general breathing/living area (yours, and animals) than you absolutely have to. But really just a pressure washer, or even one of the really good brass sweeper nozzles for your hose (which is what we used in the days before residential power pressure washers ) should do the job. Clean it more frequently in the future so stuff doesn't sit there so long.
posted by Lyn Never at 11:26 AM on October 17, 2016

Pressure washer with plain water should do this, that is what I used on my slightly dank brick patio but you do need to be careful of the mortar.
posted by jessamyn at 11:39 AM on October 17, 2016

Pressure wash, but make sure you have good ventilation that lets it all dry out well (and consider wearing some sort of breathing protection while you're running the washer). You'll theoretically be kicking up a lot of mold-like substance.
posted by QuantumMeruit at 12:25 PM on October 17, 2016 [1 favorite]

Stain Solver or other brand oxygen bleach. Will remove the gunk and not harm plants. It becomes inert very quickly. I use it to clean the wood deck before sealing and other tough stain cleaning jobs around the house.
posted by tman99 at 12:27 PM on October 17, 2016

If it's anything like the concrete patio in the shaded back yard of my last house, the green is primarily algae, not mold. A pressure washer will knock it off fairly easily. I'd steer away from vinegar if possible, because the Portland cement in the mortar is vulnerable to acids.
posted by jon1270 at 1:49 PM on October 17, 2016

Specifically, a hot water pressure washer might be just the thing you need here.
posted by workerant at 8:50 AM on October 19, 2016