Any ideas? I've read about WET & FORGET, but it takes like 6 months to work. And the other idea with a pressure washer just ends up making the concrete rough and takes some of the coating off.

Any other ideas?

 

If it really is mold, bleach will kill it. It will also probably kill the surrounding vegetation, so care is needed. Mix in varying strengths according to how bad the mold is. Bleach will not act as a degreaser, so if there is oil, that will need a different product.

 

Thanks. I just really didn't want to wait 6 months for wet & forget to work. I still can't believe it does.

 

Jason if you pressure wash at a lower pressure it will not rough up the concrete much. Like Blue said use bleach after the pressure cleaning. Plus wet the area next to the area that will get the bleach and this will reduce or eliminate the killing of the surrounding vegetation. TSP (tri sodium phosphate) is another chemical that works very well. Can be bought at any paint store or Home Depot.

 

Pressure washer will do it. Just need 3000 PSI or better to make the job easier. I have used spray and forget and it does not take a full 6 months. It only take a few days to a week to fix green and black spots I get by my AC units and gutter splash pads.

 

What about forcing the mold farther into the porous concrete with the pressure washer? I don't know if this is true for a fact, but I've heard with softer stone (limestone, soapstone) that pressure washing is a bandaid and could even make it worse. Same guy said you need to spray with some sort of an herbicide while doing it to really kill the mold.

Any professionals?