Sprinklers
The number one cause on street-parked cars. Landscaping sprinklers run at dawn, spray the same side of the same car every day, and the water is usually harder than tap water.
The tell is a concentrated pattern on one side of the car only.
There are three levels. Mineral deposits sit on top of the paint and come off with a wash or a mild acidic remover. Etching is where the mineral has bitten into the clear coat and left a crater — that needs polishing. Bonded staining is somewhere in between and often responds to decontamination.
The fingernail test tells you which you have: wash and dry the panel, then feel the spot. If it is gone, it was a deposit. If you can feel a ring or a dimple, it has etched and no cleaner will fix it.
San Francisco water is hard enough that this is one of the most common paint complaints we see, and sprinkler overspray on a street-parked car is its most reliable cause.
Water itself does not stain paint. What stains paint is what is dissolved in the water — calcium, magnesium and other minerals in tap water, plus whatever the droplet picked up on its way down. When the water evaporates, the minerals stay behind in the exact shape of the droplet.
That is stage one and it is harmless: a deposit sitting on the surface. The problem is what happens next. The concentrated mineral, sitting under sun on a hot panel, becomes alkaline enough to attack clear coat. Given enough heat and enough time it eats a shallow crater. Now the mark is not on the paint, it is a hole in the paint, and the only way to remove it is to level the surrounding clear coat down to its depth — which is polishing.
Heat is the accelerator. A droplet that dries in the shade on a cool morning usually leaves a deposit. The same droplet on a black bonnet in direct afternoon sun can etch in a couple of hours. That is why the standing advice is never to wash a car in direct sun, and why letting a car air-dry is a bad habit rather than a shortcut.
The number one cause on street-parked cars. Landscaping sprinklers run at dawn, spray the same side of the same car every day, and the water is usually harder than tap water.
The tell is a concentrated pattern on one side of the car only.
Washing and then letting it dry in the sun puts hard water on every panel and then bakes it.
Entirely avoidable, and the reason we dry by hand with towels.
Fog carries salt near the coast. It deposits, then partially dries, then re-wets. Common in the Sunset, the Richmond and along the coast.
The first rain after weeks of dry weather carries the most airborne particulate. It is the dirtiest rain of the year.
Panels get hot enough that water evaporates before it can be dried off. Every spot dries in place.
Parking under a balcony, an air-conditioning unit or a downpipe means repeated deposits from water that has run over concrete and metal first.
Always start at the least aggressive step that could work. Going straight to polish removes clear coat you do not get back.
A proper wash removes a surprising share of fresh mineral deposits. Do this first and reassess — a lot of what people are ready to polish out comes off in the wash.
Feel the remaining spots. Smooth means deposit; you can still fix it chemically. A detectable rim or dimple means it has etched into the clear coat and only polishing will remove it.
A mildly acidic product that dissolves the mineral. Effective on deposits, useless on etching. This is done panel by panel, out of direct sun, and rinsed thoroughly.
Iron decontamination and a clay bar for anything bonded. This catches the middle category — spots that are not just sitting on top but have not eaten into the clear coat either.
For etching. A polish levels the clear coat around the crater until the surface is flat again. This is paint correction, it removes a measured amount of clear coat, and it is quote-only for that reason.
Whatever step you finished on, protect the paint. A sealant or ceramic coating means the next mineral deposit sits on the protection rather than on your clear coat, which is the actual long-term answer.
| What you have | What it needs | Price |
|---|---|---|
| Fresh deposits, smooth to the touch | Exterior wash & protection | $100 / $125 / $150 by size |
| Bonded deposits that survive a wash | Add iron decontamination and/or clay bar | Iron $75–$125, clay $50–$100 |
| Etched spots you can feel | Paint correction, paired with at least a 12-month sealant | Quoted after we see the paint |
| Recurring spots from sprinklers | Fix the parking, then protect the paint | Coating packages quoted |
Paint correction is quote-only and is never sold on its own — correcting paint and leaving it unprotected is not something we recommend, so it always comes with at least a 12-month sealant.
Send us a photo taken in indirect light, plus what you felt in the fingernail test. That is usually enough for us to tell you whether this is a wash, a decontamination or a correction job before you book anything.
It is a genuinely useful distinction, because the price difference between those three answers is large.
More short answers live on the FAQ.
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The fix is drying the car and keeping protection on the paint. We do both, at your address.