I would start with 64oz per 40 gal mix and increase as you see fit, and yes all the additives hurt the potency of the SH except TSP which strengthens it and fights it at the same time. But Surfactant such as dawn only hurts the potency a little and you probably won't even notice.
Too much surfactant or TSP on a tile roof will leave a noticeable film behind, hopefully one of our Florida tile roof cleaners can comment on this and give you some more info as well.
cheers mate...ill start with that ratio you mentioned...
this film you were talking about...is it common...
hard to remove??
The film you sometimes get on Tile Roofs goes away with a couple of rains. On most all Tile Roof Cleanings you will never see a film. The ones that you will see it on are the ceramic type Tiles such as these.
I agree. There is always film left over and it will go away with a few hard rains. Too much surfactant will bog down your application. You'll just have to find the right mix that allows you not to use too much chemical and keeps it on the roof longer. Wish I could tell you exactly how much to use but it also depends on your set up. I'm shooting out of 12V FATBOYS.
Personally, I would rather shoot a bit more chem on a tile roof than bog down my flow.