How Water Spots Get Etched Into Paint

We’ve outlined to a great extent just how water beads resting on your finish dry into water spots that stain and etch your paint. But etching isn’t caused by water spots alone—insect remains, bird droppings and acid rain can all etch your finish as well. So how exactly does an etch occur? We’re going to get into the science of it here, using the water spot as an example.

From mineral deposit to stain

When a water spot first dries on your finish, it leaves an accumulation of mineral content not unlike a coffee stain. As we’ve mentioned in previous articles, these are pretty easy to remove since they aren’t bonded to the finish. But the longer the spot sits under the beating sun, the more UV rays react with the minerals in such a way that they bond to the finish. The stain’s bond can be broken down chemically, but mechanical removal through claying and buffing may also be necessary to fully remove the baked-on residue.

From stain to etch

Let’s say the water spot isn’t removed while in the stain stage, and UV radiation continues to hit the bonded minerals. What happens then? UV rays can cause a reaction in the minerals that raises the pH level, which is what determines how caustic (harsh) a solution is. At a high or low enough pH level, a solution will literally eat through solids it comes in contact with, forming an indentation in the surface. That’s an etch mark.

As mentioned above, it’s not just high pH (aka alkaline) solutions that etch. Low pH (aka acidic) solutions also chew through finishes—think insect remains, bird droppings, acid rain, even leaves from a tree!

Breaking the cycle

So how do you keep this process from occurring in the first place? Use a ceramic coating (like Dr. Beasley’s Nano-Resin) that either sheds beads easily or sheets water outright. If there’s no beads, there’s no water spots. If you don’t have a coating like that, you’re going to have to get rid of the spot before it can start etching. How do you do that? Check out our article on how to remove water spots on a car!


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