I'm going the John Hyatt route and building coats with TWP on my ipe deck. I put down the deck and did 3 coats late last summer. I was thinking about adding 1-2 more coats now to keep it looking good. Currently the finish isn't 100% like the day I put it on but it's pretty much maintained its color (just seems dirty and a little uneven in the sunniest areas).

Question - is any prep needed? I was thinking of just trying to get the dirt out with water, scrubbing and maybe a little dish soap...then thoroughly rinsing and letting it dry. Do I need oxalic acid or anything like that? Is soap a bad idea if used sparingly? Thanks.