Washing a white car: what to watch for

The grey film along the bottom

On a white car, you can see exactly how high road spray reaches. After a week of wet driving there is usually a grey band along the rocker panels, the lower doors and the rear bumper. It is a mix of brake dust, tire rubber, oil and fine grit. In winter it turns pale and crusty because of the salt.

This film comes off with a normal wash if you do not leave it too long. Left for weeks, the oily part bonds to the clear coat and a touchless wash may only lighten it. Washing regularly is easier than scrubbing it off later.

Tar spots

Small black or brown dots behind the front wheels and along the lower doors are usually road tar, flung up from freshly paved or patched roads. London has plenty of those in construction season. On a dark car you might never see them. On white they are obvious.

Tar does not dissolve in car soap. Use a tar and adhesive remover made for automotive paint: apply it, give it the time on the label, and wipe gently with a soft cloth. Do not pick at tar with a fingernail or scrape it, because that drags the grit inside the tar across the paint. Wash the area afterwards so the solvent does not stay on the clear coat.

Orange specks that will not wash off

If you see tiny rust-coloured dots scattered across the paint, mostly on the rear and lower panels, that is usually iron fallout. Hot particles from brake rotors and from rail lines settle on the car and embed in the clear coat. Then they rust. Run your fingertips lightly over the paint after a wash: if it feels rough like fine sandpaper, there is bonded contamination.

An iron remover spray dissolves the particles chemically. It typically changes colour to purple as it reacts, which is satisfying to watch on white paint. A clay bar with lubricant removes what is left. Both are worth doing once or twice a year, and they leave the paint smooth enough for wax to bond well.

Yellowing

Modern white paint under a clear coat does not usually turn yellow in itself. When a white car looks yellowish, it is often a film of road grime and old wax that has built up, or yellowing on plastic trim and headlight lenses. Older cars with single-stage paint, which has no separate clear coat, can genuinely oxidize and chalk. If a cloth with polish turns white when rubbed on a hidden spot, you probably have single-stage paint, and a professional is the right person to restore it.

How often to wash

White cars look dirty sooner on the lower half and later on the top. A good rhythm is every week or two in winter and every two to three weeks the rest of the year, adjusting when you see the grey band forming.

• Wash regularly so road film never bonds to the lower panels.
• Include the underside in winter: salt goes where you cannot see it.
• Use a tar remover on black dots rather than scrubbing.
• Decontaminate with an iron remover and clay once or twice a year.
• Protect the paint afterwards so the next wash is easier.