Quote Originally Posted by High_Plains_Drifter View Post
It's cement... and I'll tell ya, you wouldn't touch the dark green/black mold that grows on it by just scrubbing. It's on the north side of the shop so it doesn't get much light, and even though it's got a decent pitch to it so the rain runs off, that dang mold still grows. The power washer with 3,100 psi is the only thing that will touch it.
I presumed it was wood.

In this case, get some granulated chlorine from a swimming pool supply place.
Scrub that on. That is how we treated our pool decks at the training center.