I think it chemically prepped the black areas, but it left a slight white film. Maybe it's supposed too. The instructions say to spray off with pressure washer until no more bubbles. I used a soft brush on a medium handle and a spray hose, and it took literally about 10 passes to get it to stop making bubbles when spraying off. A lot of work!The first couple passes I used a regular restaurant detergent similar to simple green. I used this product full strength on part, and then just spread it around with the brush on top of already wet surface for the rest. I don't think it needs to be full strength, because it acted the same at least from a macro level and it doesn't look like it is highly pH dependent, though the msds did say an acid in it. It stinks quite a bit and so it seems to be some chemical activation.Anyway, it takes forever to get the bubbles to stop, but I wanted to do it 'right'. It definitely cleans it better compared to scrubbing with rubbing alcohol, so it was doing something. I wouldn't recommend skipping it before any of the acrylic based roof coatings. I've heard of them peeling up without good prep from an honest dealer repair shop. There are a couple of actual 'rubber roof coatings' that are made of rubber, not just acrylic to coat a rubber roof (see the ambiguity of that name?). They are more expensive, but could probably save from a full roof redo. Don't use the silicone coatings like the Henrys Tropicool at home depot, because nothing will ever bond to it without some major chemical activation.Time will tell. I'll try to update if I see any major differences in the test areas after 5 or 10 years if possible.
Rating: [5 of 5 Stars!]