I went back last night and used roof mix, scrubbed it all and rinsed with Jrod (800-900 psi) a single board with. Checked today and it is not as yellow but very clean. My concern wasn’t stains but changing its color from grey to yellow. Its a extremely light grey now. Composite is easy to clean but 1st generation Trex is entirely different. It will definitely lighten in color and know I can say it can even change color or bleach out.
Today’s pic
Looks way better!
Now that it’s clean can try hitting it with oxalic - 8oz to a gal. Let it dwell about 15min and then rinse well with hose. Then they’ll have something that is way better and paintable.
I tried that exactly before I hit it with the roof mix and it didn’t do anything. I only did it in a few test spots but I didn’t see any difference. The other thing I had to do was rinse the heck out of it. Dirty water is what contributed to the nasty look after the first wash. It’s so porous the water was staining it after it dried.
It’s a shore home and the owner won’t be down for a couple of weeks. I explained the problem with 1st gen Trex and he understood completely. Hopefully when he sees it he is ok with how much it lightened.
@Racer, is there a way to differentiate, aside from asking age of the deck, between 1st gen or older trex/composites and newer ones? Is it readily apparent or need a well seasoned eye? I have also stayed away from composite for fear of harming them. Great info here.
After you see one you’ll know. They always seem black with mold even though its not all mold. They can feel a rough or more porous than newer composite. I wouldn’t worry too much about changing color because I’ve done hundreds of 1st gen and never had this happen so it is probably rare. Do a test spot with chems, let it sit and rinse. It will lighten just let the customer know.
Read above, newer is fully encapsulated
I understand this is a couple years old (doing my research 
) but I have a very large deck like this coming up this week. When you went back to scrub this, was it with a soft brush just to agitate the mixture and get it down in a little or did you use a hard bristle brush to aid in cleaning? Someone had used a surface cleaner on this deck last year and I can see the swirl marks from where they had gone too fast (missed) and where they stopped under the railings. So, I know pressure will clean some of it but I warned the guy that damage may have been done. I also see the spots that you have shown. I’ve seen them before on older composite. The house/deck was built in 1994 so they aren’t expecting miracles but I want to wow them if possible as it is the founder of a commercial company that I have been doing some work for. It could give me a lock on many future jobs.
The brush was more of a stiff bristle deck brush. It helps to clean not so much get the mix in deeper. I like using the brush instead of a dangerously strong mix or hitting it with more pressure. I won’t scrub the whole deck but just the bad areas. Just remember it won’t look good till it dries. So don’t keep adding pressure or sh thinking it’s not clean enough. (This is all for 1st gen composite)
First gens are old and fragile, I cleaned one for the first time, a red one and I was so disappointed when i couldn’t get the black spots off. Once it dried it was all gone and a bright red color. Looked dang good!
Same thing when I did my first gen deck. I got so frustrated and went on to clean the rest of the house. I came back and it was great. I always say let it dry before you do something crazy.
