I know its just pressure treated lumber but has anyone cleaned with chemicals the frame work of a check and what was your method/technique?
Pretty much everything you could ever need to know about cleaning wood can be found in this thread.
I do it and some turn out good and some not so good. We use our dedicated pump if it’s a big deck but mostly use a pump sprayer. I usually do a strong mix of 50/50 water and SH. I’ve had some come out clean with just a strong house wash mix too. Just hit it and if it doesn’t come out to your expectations increase your sh.
A couple of months ago I discovered by accident that going back and hitting the boards with SH a second time often pays HUGE dividends. AND, after the second treatment I don’t need to hit each board again, just rinse off the SH and follow with OXALIC ACID. I typically use my downstream system and go 4-6 boards ahead, then hit each board usually 1/2 width moving quickly from one end to the other, return in the other direction cleaning the other half. If still ugly, I follow that with another treatment of SH, rinse, and brighten,
I would think SH it all , wash it pretty good with higher pressure if you can because the treated can handle it. then ox acid after . I guess it all depends how dirty your boards are