Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

We got off to a late start this year but my grandfathers pool has finally been opened.

Anyway, the patio surrounding the pool consisting of 1 foot cement tiles hasnt been cleaned by more than a hose for nearly 40 years. Some of these stones, which probably used to be whitish, are black, and the remainder are thickly covered in moss. My question is this, if we were to rent a powerwasher(or more likely borrow a 9HP unit from my contractor), what amount of power would be neccesary? Also, what type of cleaning solution is needed, if any, to get these cement squares back to there original color, and to try to keep the moss away? What rates do the high end units rent at? Is their anything else I should know(other than don't touch the stream)?

Thanks,

Mike