Suggestions for pressure-washerconcrete pre-cleaners

[Uncle Cracker]

Looking for a good pre-made or homebrew pre-cleaner/treatment for use on outdoor concrete (driveway & sidewalk). Must be safe for runoff onto the lawn. I'm loaning my washer to my neighbor, and he has areas with substantial shade that are darker (black, not green) than anything I have to deal with on my property. I suspect some kind of algae in these areas. My neighbor would rather spray/spread something in advance of washing, rather than use the chem injector on my washer.

Anybody got any suggestions/recipes?

[LCHIEN]

on my patio, i get black mold from dampness.
I periodically clean it with mold and mildew remover i spray with a simple hose- attached sprayer. What I find really helps is to take a bucket of water and mix about 5% bleach and slosh that over the patio to kill most of that mold - let it sit for a while to kill the mold before spraying the mold and mildew cleaner on it. It didn't seem to hurt the grass adjoining the patio too much. It may not be perfect but it will lighten considerably over the next few days.

I have borrowed a pressure washer and that just blasts the mold off one square inch at a time, very slow and laborious and you end up with streaks.

p.s. With the mold and mildew cleaner concentrate (by Zinser?), you mix bleach into the sprayable solution as well.

[tommyt654]

Ditto on the bleach and I use some Simple Green mixed in with it as well, but its slippery as heck with that brew on top of wet wood, I,d advise some shoes with tread of some sort and old jeans as the bleach will splatter.

[Tom Slick]

Try a 1 cup of Borax (found in the laundry detergent aisle) and a tablespoon of soap per gallon of hot water.

It works great on my fence and is cheap. It can be a little rough on the lawn but with plenty of water shouldn't hurt it.

[cabinetman]

I haven't found any pre-spray cleaner that won't kill the grass. Clorox for sure will do a number on the mold and algae, but will also kill the grass. If you offer a suggestion as a good will effort to accompany your pressure washer, it may turn out to bite you. It's that neighbor thing.

Personally, I would leave decisions like that up to his own devices. You are nice enough to lend your equipment, and suggesting he find out on his own. The bonus points for suggesting a solution that works isn't worth the liability of finding out it doesn't.

I just use the best tip and get the distance right not to leave streaks.
.

[Uncle Cracker]

Thanks guys... Yeah, the bleach thing was worrying me. I figure any strength enough to kill algae would probably not be good for the grass (and his grass ain't in such great shape to start with). As for the nozzle, I have one of those 16" rotary rigs with wheels and two spinning tips. It works fine on mine, but I don't have anywhere near the "soot" that he does. Maybe I'll just tell him to plan on doing his twice...