Rennlist - Porsche Discussion Forums - Bilt-Hamber Auto-Foam Process

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Once a vehicle has accumulated a significant amount of film traffic dirt and road grime and you run the risk of inflicting sub-surface paint scratches during the wash process. This is due to the greater number of contaminants present that may inadvertently be moved around as they are removed, and the tendency to use more friction on paint surface to get it clean.

You can mitigate these risks by rinsing off as surface much dirt and grime as possible using a hose or a pressure washer before washing the bodywork by hand. Ten to fifteen minutes spent carefully rinsing off in this way is time well spent, the use of a pre-wash foaming solution can help tremendously.