First Deck Wash Before and After Pics + question about green stuff

Question: This is in Minnesota and there is some green stuff on some of the cedar boards. I hit it with a strong mix of Percarb, and the Brightner. When that didn’t work I tried applying and scrubbing spots with a strong mix of SH- nothing worked. In the end, the homeowner was satisfied but the green stayed.

Any advice? What is it?


Cort Pressure Cleaning
Minneapolis/St. Paul

First off the deck looks great Nice job. I don’t see the green stuff your talking about in the picture but if your talking about the knots in the wood looking dark after the cleaning thats common and I wouldn’t worry about it.

Hi Darin,

The only answer that makes sense is you are seeing an existing, old, weathered stain. If it is oil based, a light 6 - 8 oz. of sodium hydroxide / gal. of water should remove it. Re brighten with a subsequent acid wash.

The treatment process can sometimes leave a green tint to the wood. It does not clean off. That deck looks great!



The wood is cedar, not pressure treated SYP.

Not sure how I missed that. Sorry about that!