So what are some tips for pressure washing decks? I'm fairly confident with it comes to driveways and siding, but I'm a little nervous to do my first deck for a paying customer. Case in point: The deck on my house is probably more than 20 years old. It was built before I owned the home. Non-treated boards, no stain or other coatings that I could tell. I used some deck wash detergent, 5 gallons mixed sprayed over probably only 400 sq. ft including a small section of fence. I stayed under 1200 psi, with a 25° nozzle. The manufacture of the deck wash suggested going in a sweeping motion against the grain, but I've read a lot that says with the grain. I basically did a half dozen boards alternating between with and against. I got a lot of marks where I apparently didn't feather good enough going with the grain, yet against the grain looks great. I had enough room I could have done the entire board with one pass, which may have solved the problem with the marks. Another problem was that I seemed to have some residue left over. I went over some of the boards several times and still seemed to push detergent out. If anyone is willing to lend some advice, I would greatly appreciate it. I tried to get a couple before and after pics, but the attachment feature wouldn't cooperate with me.