Bilt Hamber Auto-Foam is an alkaline but non-caustic pre-wash you apply before the contact wash. You dilute it, lay it over the cool paint and rinse off the loosened road grime after a few minutes. That means you touch far less grit during the wash, which is what prevents scratches. You will find Bilt Hamber Auto-Foam in the shop.
What Auto-Foam does
Auto-Foam softens the layer of grit, dust and road film that builds up on your car after a drive. It works through the cleaning chemistry, not through the thickness of the foam: the surfactants surround the dirt so it lifts away when you rinse. Bilt Hamber stresses that the product is alkaline but non-caustic, and that last part matters. Caustic cleaners based on sodium hydroxide can attack the paint film; Auto-Foam is safe on most surfaces treated with wax or polish. Bilt Hamber backs that up with their own Double Speed-Wax, which survives dozens of washes with Auto-Foam. On a ceramic coating, do a small test spot first, since the maker cannot test it against every coating on the market.
Why a pre-wash prevents scratches
Most swirls and fine scratches do not come from the shampoo, but from dragging grit across the paint during the contact wash. Every particle still sitting on the panel when your wash mitt passes over it is a fine scratch waiting to happen. A pre-wash like Auto-Foam chemically removes most of that loose dirt before you touch the paint. The less that is left, the safer the actual wash. On a dirty car in winter, that is the difference between clean paint and paint full of light marring you have to polish out later.
How to use it
Dilute. Mix around 4% Auto-Foam with water. A lightly soiled car may need only 1%, a heavily soiled car moves toward 5%.
Cool and shaded. Work on cool paint, out of direct sun, so the product does not dry on. Pre-rinse the car first to flush off the loose grit.
Apply. Lay down an even layer with a foam lance on your pressure washer or with a simple pump sprayer. Work bottom to top so you cover everything.
Dwell and rinse. Leave it for a few minutes, around five works well and longer is fine. Then rinse thoroughly with the pressure washer before you start the contact wash.
Foam lance or pump sprayer
A thick blanket of foam looks impressive, but it is not needed for the cleaning to work. Auto-Foam cleans just as well applied as a thin solution from a pump sprayer, without a foam lance. The cleaning is in the chemistry, not the bubbles. So if you do not own a lance, an ordinary garden or pump sprayer is a full alternative. If you prefer to work out the dilution exactly: 4% in one litre of water is around 40 ml of Auto-Foam, so for a larger mixing bottle you scale that up in proportion.
Auto-Foam or a pH-neutral snow foam
Auto-Foam is a stronger, alkaline pre-wash for when the car is genuinely dirty. If you want the gentlest possible pre-wash on a coated or waxed car, a pH-neutral snow foam such as the Koch Chemie GSF Gentle Snow Foam suits weekly upkeep better. Not sure which approach fits, then read how to use snow foam first for the complete pre-wash step. You will find more pre-wash options in the snow foam and pre-wash category.