On wood I used a brush to apply. It was mostly to apply evenly than to actually scrub. Scrubbing was not necessary. I tested a few out of sight spots first and determined that leaving it on there more than a minute(60 seconds) and it did too good of a job (if that makes sense) I had a charged water hose handy for quick rinse. stone/cement will surely take a little longer. I would do like I did and find an out of sight test spot if that's possible to experiment with initially. Sure hope it works for you. Good Luck.
"The Poor Fish" circa 1930's: The Poor Fish wouldn't have been caught if he'd known enough to keep his fool mouth shut.
"Opportunity is missed by most because it is dressed in overalls and looks like work"- Thomas Edison, businessman/inventor