Auto Detailing - November 2007

Prep Wash—A Seemingly Simple Procedure
By Prentice St. Clair

In our competitive world, detailers can become so focused on technological advances, new product introductions, and the latest management trends that they lose sight of the basics. The prep wash is an example of a basic detailing procedure that deserves to be revisited.

Automotive detailing can be described as the cleaning and protection of the vehicle’s surfaces. So the first part of any detail is cleaning. As far as the vehicle exterior is concerned, the initial cleaning step is the prep wash. There are distinct issues surrounding this seemingly simple step in the complete detailing of a vehicle.


The purpose of the prep wash is simply to prepare the vehicle’s exterior for detailing by removing excess surface dirt and grime. A common misconception is that the prep wash must remove every last spec of grime, staining, and surface contamination from the vehicle. In fact, the prep wash will not remove all stains and surface contamination, but will get most of the loose stuff off, clearing the way for the use of other detailing chemicals that can remove remaining contamination.

The exact procedure that you use to prep wash a vehicle depends upon many factors, including how dirty the vehicle is upon arrival, the configuration of the prep wash area, and the equipment and chemicals that you are using. Ultimately, you will develop a prep wash procedure that is the most efficient and effective for your situation. Even if you have been detailing for some time, my hope is that you will pick up a couple of ideas that will help you improve your prep wash procedure.


If at all possible, the prep wash should be conducted in a dedicated area. It’s awfully difficult to conduct the remainder of the detail in an area that contains the water, dirt, and grime run-off from the prep wash. A higher volume detail operation can have dedicated equipment, chemicals, and technicians in the prep wash area. This approach is very efficient when it is executed with clear standard operating procedures performed by trained technicians.

If your detail operation is part of an automatic car wash, your prep wash is simple — just run it through the tunnel. You may need to spend some time (pre-tunnel) applying extra cleaning agents to the front grill, wheels, and wheel wells, but you are still the envy of those of us who must prep wash cars by hand.

Automatic car washes typically do not remove as much of the surface contamination as a thorough hand wash does. You may have to spend extra time during detailing to make sure that the surfaces are clean. Moreover, some technicians prefer to hand wash vehicles being prepared for detailing, despite the existence of an on-site car wash. Still another approach is to wash the dirtiest parts of the vehicle, like the engine bay, wheel wells and wheels, and doorjambs first with a pressure washer, then run the vehicle through the automatic car wash.


A common mantra among the motoring public is that a vehicle should be washed “from top to bottom.” For the professional detailer performing a prep wash, however, the mantra should be “wash the dirtiest parts first.” As the dirty areas are blasted clean, some of that dirt and grime will splash onto the “cleaner” areas, so it makes sense to wash the cleaner areas last.

Most agree that the prep wash begins with an initial vehicle rinse-off. However, if you are not working in the sun and the vehicle is not very dirty to begin with, you can save time and water by starting the prep wash without an initial rinse. At the other extreme, if the vehicle is coated with mud, the initial rinse is quite important as a means to remove as much surface mud and dirt as possible before continuing with the prep wash.

If the detail job at hand includes work in the engine bay, wash the engine first. As you clean the engine, moisture from the pressure washer as well as oil and grime will splash onto the remainder of the vehicle. It makes sense to get this done before proceeding with the prep wash.

The first place to wash (after the engine bay) is the doorjamb area. Most professionals agree that even the most basic exterior detail includes cleaning the doorjambs. Spray the hinge areas with degreaser and rinse them off. If you are concerned about splashing into the interior of the vehicle (especially if the interior is not to be detailed), you can rinse the doorjambs by closing the door and pointing your pressure washer at the door seams. The remainder of the doorjamb can be cleaned with multi-purpose cleaner and a soft brush and then rinsed.

Next, it’s time to clean what I like to call the “lower third” of the vehicle. This includes the front grill, light groups, bumper and spoiler; wheels, tires, and wheel wells; doors and sides from the trim line down (or approximately the bottom third) and the rocker panels; and the rear light groups, license plate area, and bumper. In some higher-production operations, cleaning the lower third means simply spraying all the mentioned areas with a strong multi-purpose cleaner and immediately blasting the areas off with a pressure washer.

For retail and high-end detailing, I believe that cleaning the lower third areas requires agitation before rinsing. There are some great soft brushes and special sponges that are perfect for this work. Work with one area at a time (e.g., the front end or one wheel area). Spray the area with your favorite multi-purpose cleaner and then agitate it with a soft brush or scrub sponge. If you are working in the sun, you need to rinse the area right away. If not, you can wait until you have circled the vehicle and then rinse all of the lower area at one time.

After the lower third is cleaned and rinsed, rinse the top and then wash it using car wash shampoo and a wash mitt. Utilize a good, stable step stool for larger vehicles and a soft truck brush with a telescoping handle. Then rinse the vehicle thoroughly. At this point, you can use detailer’s clay and a new batch of car wash shampoo to remove minor surface contamination. If the vehicle has extensive paint overspray or ferrous oxide deposits, perform the clay step separately after the vehicle is dry.

Dry the vehicle with a chamois, squeegee, a large microfiber towel, or a combination of these. Then blow out the seams and crevices with compressed air (not greater than 60 psi, please!). The vehicle is now ready for further exterior detailing.

A standard prep wash on a four-door sedan should take one technician about 30 minutes to complete, from first rinse to final dry.


Water Reclamation — One of the major issues that comes along with prep washing is water reclamation. According to the Clean Water Act of the early 1970s, it is illegal to allow any water or chemical (other than rain run-off) to enter storm drains or naturally occurring waterways. The enforcement of the regulation was left up to local municipalities, and in some areas nothing has been done about enforcing the Clean Water Act for decades. This is changing.

If you are concerned about increasing pressure from local enforcement of the Clean Water Act and you do not have adequate water reclamation equipment, think outside the box a bit. Consider accomplishing your prep wash at a nearby automatic or self-serve car wash. Driving the vehicle to the car wash, having it washed, and then returning to your operation should take the same amount of time as performing the prep wash at your own site, assuming the wash is within a few miles. You may even be able to work out a volume discount with the owner of the car wash. By prep washing your vehicles this way, you avoid all of the hassle of water supply and water run-off at your site.

Full-Service Washing — The prep wash should be distinguished from the “full-service wash.” A full-service wash simply cleans the vehicle with results similar to that of a car wash. Many of the stronger chemicals used in the prep wash will not be used for a full-service wash because they can strip away the protective chemicals (like waxes and sealants) that may be on the vehicle.

Pressure Washers — Most technicians agree that using a pressure washer during the prep wash is critical. Pressure washers generally use less water than a standard garden hose and help clean the vehicle with dirt-lifting force. However, it is not absolutely necessary to have a pressure washer, especially if you are performing only high-end extensive detailing. On the other hand, a pressure washer is quite important for engine cleaning and for high-volume vehicle washing.

If you use a standard garden hose, obtain a high-quality multi-pattern nozzle, which will reduce the amount of water needed for the wash. A simple prep wash on a four-door sedan does not require more than 10 gallons of water, including the buckets of car wash shampoo.


The prep wash, at first glance, seems like it should be a fairly straightforward process. But as you can see, there are actually several issues and variables that make it a complex project. The most important thing is to set up standard operating procedures that can be accomplished in the shortest amount of time possible with the best result.

Prentice St. Clair is president of Detail in Progress, a San Diego-based automotive reconditioning consulting firm. To contact him, e-mail or call (619) 701-1100.

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