I want to apply Rain-X a water repellent to my windshield. To make sure the glass is clean first I'm going to run the car through an automatic car wash.

  1. I assume I want the cheapest external wash with no added Clear Coat Protectant or Tri-Polish Wax or other superior Premium add-ons which would coat the windshield before I added the water repellent: True or False?
  2. I assume that after I've rubbed on the water repellent (and let it dry) I can then run it through the car wash with their high quality sprayed on wax and/or coatings and that won't impact the repellency of my water repellent coating: True or False?

1 Answer 1


I use these water repellent products frequently. Typically I hand wash my vehicles, however I have used automatic car washes too. In my experience, it doesn't really matter what the car is washed with (including the windscreen) as long as the repellent product is applied properly according to the instructions afterwards.

Subsequent washing reduces the effect of the repellent product, so I certainly WOULD NOT apply it before washing, always after.

For more info, Rain-X have a good hints and tips page: https://www.rainx.co.uk/tips-and-info/

  • 1
    Note that if you apply it after washing, you should skip the wax cycle. I always clean the glass with rubbing alcohol before applying to remove any residual contaminants.
    – Comintern
    Commented Nov 22, 2018 at 16:48

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .