I am planning to restain a roof deck which sits upon a flat, asphalt roof. The deck has previously been stained with an unknown stain. I understand that I will need to clean, strip, and brighten before staining. I am concerned that whatever I use to clean, strip, and brighten will have damaging effects on the roof material. Can anyone recommend products that will be effective on the deck without damaging the roof? I am also looking for recommendations for stain. I have read that oil can dissolve the asphalt so I am leaning away from oil based stains.