Car wash or driveway: which is better for your car?

Where scratches come from

Paint gets swirled and scratched by grit being dragged across it. That can happen with a sponge, a towel, a brush or a mitt. The tool matters less than how much grit is on it. In a typical driveway wash, people use one bucket, dip the sponge, scrub the lower doors, dip it again and carry that sand back to the hood. After a few washes the paint shows fine circular marks in direct sun.

A touchless wash avoids this because nothing touches the paint. Soap loosens the grime and water pressure carries it away. The trade-off is that it cannot scrub, so a very heavily soiled car, or one with baked-on bugs or tar, may need some hand attention afterwards.

If you do wash at home, do it properly

A good hand wash is a fine way to look after a car, and many enthusiasts prefer it. The difference between a good one and a damaging one comes down to a few habits.

• Use two buckets: one with soap, one with plain water to rinse the mitt before it goes back in the soap.
• Put a grit guard in the bottom of each bucket so dirt settles under it.
• Use car wash soap, not dish soap, which strips wax and sealant.
• Wash from the roof down and do the lower panels and wheels last, with a separate mitt.
• Work in the shade and keep panels wet so soap does not dry into spots.
• Dry with a clean, soft drying towel or let it drip dry and blot, rather than dragging a chamois.

Where the water goes

Soapy water running down your driveway into the street enters the storm drain, and in most of London storm drains are not connected to a treatment plant. That water flows to the Thames River and the creeks that feed it, carrying the soap, brake dust, oil and road grime from your car along with it. One car does not sound like much, but a whole street washing on the first warm Saturday adds up.

If you wash at home, park on the lawn or gravel so the water soaks into the ground instead, and use a modest amount of biodegradable car soap. A commercial wash bay drains into a sanitary system rather than the storm sewer, which is one of the less obvious reasons to use one.

Winter settles the question

From roughly December to March, a driveway wash in London is either impossible or a bad idea. Hoses freeze, water turns to ice on the driveway, and washing a car in sub-zero air leaves water freezing in door seals, locks and mirror housings. Yet winter is exactly when the car needs washing most, because of salt.

This is where an in-bay automatic earns its place. You can rinse the salt off on a cold evening without standing in the slush, and the underside, which you cannot reach from a driveway at all, gets sprayed too if your wash includes an under-car spray.

A reasonable split

Plenty of people do both. They hand wash on a mild summer weekend when they have the time and feel like it, and use a touchless wash for the rest of the year and for quick clean-ups between. Fast Lane is open 24 hours, which suits the late evening rinse after a day of slush. Neither approach is wrong. A careless hand wash and an infrequent wash are the two things that actually hurt a car.