A car wash is a facility used to clean the exterior, and the interior, of automobiles. While there are many different types of car washes, most fall into three main groups:

Self-service facilities, that are generally coin-operated

In-Bay Automatics, which consist of an automatic machine that rolls back and forth over a stationary vehicle while washing it

"Tunnel washes", which use conveyors to push or pull the vehicle through a series of fixed cleaning mechanisms.

Mechanized car washes, especially those with brushes, were once avoided by some meticulous car owners because of the risk of damaging the finish. This perception of vehicle damage was the motivation behind the rise of the touch-free car wash facility. Touch-free car washing, however, proved to be an extremely difficult endeavor with many types of touch-free machines and extremely harsh, even dangerous chemicals that are used in order to get a vehicle clean. Many of these chemicals have the potential to cause more damage than the brush type washes they replaced. Today, buffered chemicals, improved hydro-dynamic cleaning systems and modern foam based materials for friction washes have greatly reduced the chance of vehicle damage in car wash facilities.

In a modern car wash facility, whether automatic, in-bay automatic or self-serve, soaps and other chemicals used are based on milder acids and alkalies designed to loosen and eliminate dirt and grime. This is in contrast to earlier times, when hydrofluoric acid, a hazardous chemical, was the most common cleaning agent used in the industry. There is currently a strong move in the industry to shift to safer products and rely more on friction to clean a vehicles finish. Many car wash facilities are now required by law to treat and reuse their water, in contrast to less elaborate facilities where wash water simply ends up in the storm drain and eventually into rivers and lakes.

Self Serve Car Washes

A simple and automated type of car wash is a coin-operated or token-operated self-service system. The vehicle is parked inside a large bay that is equipped with a house cleaner sprayer and a scrub brush. When customers insert coins or tokens into the controller, they can choose to have soap or water dispensed from the sprayer, or to scrub the vehicle with the brush. The number of coins or tokens inserted determines the amount of time customers have to operate the equipment, however in most instances, a minimum number of coins are necessary to start the equipment. These facilities are often equipped with separate vacuum stations that allow customers to clean the upholstery and rugs inside their cars.

The first automatic car washes appeared in the mid 1950s. Mechanized car washes consist of tunnel-like bays into which customers drive their cars. Some car washes, following the exterior express trend, allow their customers to pay through a computerized POS, or point of sale unit, also known as an "automatic cashier", which in many cases may take the place of a greeter. The mechanism inputs the wash PLU into a master computer or a tunnel master automatically. When the sale is automated, after paying the car is put into a line-up often called the stack. The stack moves sequentially, so the wash knows what each car purchased. After pulling up to the tunnel, an attendant usually guides the customer onto the track or conveyor. At some washes, both tires will pass over a tire sensor, and the system will send several rollers. The tire sensor lets the wash know where the wheels are and how far apart they are. On other systems, however, the employee may have to guide the customer on and hit the 'Send Car' button on the Tunnel Master.

While on the conveyor or track, the attendant will usually ask the customer to put his or her vehicle into neutral and release all brakes. Failure to do so will inhibit the conveyor. The rollers catch the tires, pushing the car through a photo eye, which measures vehicle length, allowing the computer to tailor the wash to each individual vehicle. The equipment frame, or arch, vary in number. A good car wash makes use of many.

The customer will first encounter one or two arches, or often called pre-soak arches. They either apply a low ph with a mild alkali, then a high ph with mild alkali. It can vary in reverse in the industry depending on chemical suppliers and formula used. Some use a kick like running it 'hot' with hot water feeds during dilution into a hydrominder of some form. Others go corrosive some being level eight and above using sodium hydroxide, phosphorus, or hydrofluoric acid which can melt glass. Of course, however, ethically, car washes are designed not to harm a vehicle's paint.

The customer next encounters tire and wheel nozzles, which the industry calls CTAs.

These will apply either a degreaser with a high alkalinity solution, or even an acid. These remove brake dust and build up from the surface of the wheels. The next arch should be entrance wraps usually made of neo-glide material. This gentle cloth, despite popular belief, will not scratch the vehicle unless something is caught in them. This is why most washes will not allow anything in the back of a truck go through their wash. These should rub the front bumper and, if programmed with a good cloth pattern, will make a swipe on each side of the rear of the vehicle cleaning the license plate. Past the first wraps or entrance wraps is a tire brush spinning at a high RPM that will scrub the tires. This is usually located beneath the mitters or top brushes.

The mitters cloth can vary greatly between perma color, micro-fiber, or more gentle neo-glide. After the mitters, the car passes through exit wraps which are just like the entrance wraps. This is where the water works begin with high pressure streams of water. The customer either passes over an under carriage wash or gets high pressure nozzles pointed up on a mounted base. Next, if available, is a tire spinner or omni spinner. These are high pressure nozzles angled and mounted on a spindle. When high pressure is forced through, it causes the nozzles to spin rapidly. If timed, programed, and adjusted correctly, the nozzles will follow the front and back rims. Past the omni spinners are the omnis-- high pressure nozzles mounted on the sides and top of an arch. These will move side to side and up and down blasting dirt from the cracks of the vehicle (not yet in the rinsing phase). After passing the omnis, the vehicle may triple foamers, usually red, blue, and yellow.

There are two types of foam: polish and wax. Polish is cheaper and may be harder to rinse off, sometimes becoming solid matter in its holding tank. Wax is more expensive, but rinses well and covers the vehicle with a lighter and puffier foam. It does offer more protection than the polish, but is not what protects overall. The next arch will be mitters to rub the foam on the vehicle. Some washes have multiple rinse stages, usually offering a protectant. Protectants vary greatly with some making water bead (or gather) and some making water sheet (or spread to a thin layer) before being blown away by a dryer. Near the rinse is where a tire shiner, which is made of foam pads that retract and have a thick oily substance pumped through them like glycol to rub across tires producing a wet or new look. Finally the vehicle encounters a spot free rinse of soft water that has been filtered of chlorine and sent trough semi permeable membranes to produce highly diluted water that will not leave spots. After using spot free water, the vehicle usually does not require hand drying. The wash often finishes with this drying, and a light usually indicates for the customer to leave.

Old-style automatic washes used rotating brushes with soft nylon bristles, but these tended to put faint scratches in the vehicle's paint. Some brushes are made of soft cloth, and these will not harm a car's finish. The most current technology is a foam based brush (called a "wrap"), which is resistant to this when properly lubricated with water. In order to avoid scratching issues, "touchless" or "no-touch" car washes were developed. They use high pressure water and strong chemical detergents (higher or lower on the pH scale), particularly hydrofluoric acid to clean the car. Touchless car washes may not fully clean very dirty cars, similar to washing your hands, but never scrubbing them together.

At "full-service" car washes, the exterior of the car is washed mechanically with conveyorized equipment, but attendants are available to dry the car manually, clean any spots the equipment has missed, and to clean the interior (normally consisting of cleaning the windows, wiping the front and side dashes, and vacuuming the carpet and upholstery).

Some car washes now are “no touch.” This means the car is washed with high water pressure instead of actual machine equipment. This new type of car wash may seem better for your car because no cloth is touching the paint. But, it really does not clean a car as well because some dirt needs cloth to get it off and water pressure will not do that. Also, manually drying you car will get off that dirt that does not seem to want to come off. It gives you the opportunity to give extra attention on places that need it.

For areas where water conservation has been implemented, it may not be possible to wash the car with water, and hence a method of waterless car wash has become popular.