I pressure wash (1300psi) my deck (pressure treated) every 2-3 years
since it was built depending on how dirty it gets. No ill effects yet.
I just use water and it gets everything off just fine. I've sealed it
twice, once when new and once since then. It is due for another
sealing but it can wait till next spring. My deck is 13+ years old and
looks damn near new. Just don't get too close with the washer head.

I have found that washing chemicals can cause discoloration on vinyl
siding, so bear that in mind. Otherwise I've found no problems power
washing anything (deck, drive, walkways, siding, etc.).

Good luck.
`Casper


lbbss muttered:
I head conflicting advise on maintaining my deck. Some say you
damage the deck by pressure washing it. Does pressure washing it
remove the pressure treated chemical out of the wood? Also, If you do
wash it is detergent required? Our deck is in good shape except in a
few shaddy spots, it has mildew. I was going to pressure wash it
then seal it. should I not pressure was the fence if I don't plan to
seal the fence? Thanks.