Hand versus machine: Which is better at the car wash?

From grade-schoolers raising a buck for the band, to an owner in the driveway with a hose and a sponge, the art of the car wash has been around for as long as… well, as long as the car.

Some folks are meticulous about keeping their cars clean. Others wait for the next rainstorm to do the job. But for those of us who question Mother Nature’s detailing skills, what’s the best wash method? Does the TLC of a hand wash in the driveway outweigh the convenience and ease of the automatic/drive-thru wash?

Not a chance, at least according to a study from the University of Texas at Arlington. “The results are depressing, at least to the car owner who, up to now, has firmly believed in hand washing,” stated the study. “…Under the microscope, the paintwork (after hand washing) looked like a cratered landscape. The paintwork was deeply scored and scratched — the result of dirt and trapped sand particles.”

The two cars used in the study (it’s an older study, but one that is still relevant) were each washed 25 times — estimated to be a year’s worth of car washes — one by hand and the other by machine. The paint “scars” were then examined by microscope on both vehicles.

“By comparison, the surfaces of the test vehicle washed with automatic car washing equipment appeared different,” the summary read. “It was remarkably smooth, the result of evenly moving and rotating cloth pads and curtains.”

The study also suggested that the garden hose used by do-it-yourselfers in the driveway is unable to supply enough water or pressure to safely remove dirt without injuring the vehicle’s finish.

Experts say if left unattended — especially in the hot sun — acids in bird poop, bug guts and tree sap can do serious damage to the finish.

And that was our call to action to test out a couple of theories on an Audi R8.

What’s in the foam?

While the University of Texas study indicated automatic/drive-thru car washes are the safest, thoughts of vehicle damage and the great unknown of what the heck is coming out of those spray nozzles might make you squeamish at the wash entrance.

Sure, the colourful foam that looks like regurgitated cotton candy smells curiously nice when drizzled onto your vehicle — usually like lemons or medicinal bubble gum — but what is it?

Wash “soap” is a basic mix of Sodium Dodecylbenzene Sulfonate, Neodol, a surfactant, a little added scent and water. All of which sounds like a mad chemist’s cocktail but is actually benign when mixed properly.

The first mouthful, Sodium Dodecylbenzene Sulfonate, is a common ingredient in laundry detergent that helps to loosen the dirt when mixed with water. Neodol is widely used in surface cleaners and helps give the car a waxy protective finish. And the surfactant helps the water work peacefully with the detergent in the cleaning process.

The familiar conveyor-type car wash has been around since the late 1930s and has been evolving ever since. Today, they operate on with an intricate system of mitter curtains, lasers, computers, scrubbers, nozzles, hydraulics, brushes and dryers.

Mitter curtains are the long, soft, stationary strips of cloth that hang near the entrance of the wash tunnel. Scrubbers are the large, rotating cylinders with hundreds of small cloth strips attached to them. These rotate and a high rate of speed, up to 500 revolutions per minute, and would feel like a whip if you decided to roll down the window for a touch.

Older automatic washes typically built before 1980 used brushes made with soft nylon, but which often left marks on the vehicle’s paint. Newer washers mainly used cloth with a slight pendulum action to wash the vehicle. The cloth is less harmful to vehicle paint, provided it is frequently flushed with water to remove grit from previous washes.

Touchless wash systems use high water pressure to clean the vehicle instead of brushes, perhaps lessening the chance of surface damage. In some cases, the nozzles of each jet are arranged in a pinwheel fashion and the incredible force of the water — up to 1,000 pounds per square inch — rapidly spins these wheels to create a circular pattern and the necessary cleaning action.

Many “full-service” car-cleaning operations include interior vacuuming and detailing as well as hand drying. But be warned because Consumer Reports offers one strong piece of advice for the hand-drying service: if the towel isn’t clean, there’ll be no sheen as a dirty drying towel is an invite for scratches.

Newer high-pressure washes can use hundreds of litres of water per car, but to conserve water and reload for the next wash, the systems usually have a pressure tank situated nearby to recapture and recycle the water through a filtration process.

Once the car is washed, a protective wax is often applied (it’s usually optional) that is different from over-the-counter wax brands because it is formulated to also work on glass, chrome and rubber, though it is unlikely to provide the same level of protection or help to cover up or repair tiny scratches as standard wax does.

Old habits die hard, and the results of one study might not persuade driveway do-it-yourselfers from changing their ways. In our little experiment, the touchless car wash performed surprisingly well, but left brake dust on the wheels and a few bugs on the grille.

But one thing is clear: given the choice between potential hazards from birds, bugs and trees, or those from either type of car wash, always choose the latter.

The vehicle:

A not-quite-white Audi R8 seems like the perfect way to test two wash methods. The passenger side was hand washed (including the roof, hood and hatch), pictures were taken, and then the car was driven through a touchless automatic car wash to compare.

The wheels:

Machine washing left some brake dust on the wheels compared to the cleaner hand wash. When it comes to wheels, hand washing is the winner.

Insects and dirt:

The machine wash did a pretty good job at getting the dirt off the rear, but since the automatic car wash can’t see them, it didn’t get all the bugs off.

The verdict:

Hand power wins over machine.