Auto Laundry News - August 2013

IDA Certification — Study Guide: Prep Wash

By Prentice St. Clair

In this month’s column, I would like to cover the information needed to successfully complete the “Prep Wash/Wash Bay” portion of the detailing certification exams offered by the International Detailing Association.

The International Detailing Association offers its Certified Detailer program to both members of the association as well as non-members. The program currently consists of 10 tests that assess the taker’s background knowledge of detailing. This month’s column is one in an on-again, off-again series that is designed to present a study guide for those who are interested in taking the tests. Get more information or sign up for the tests at

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. This is a seemingly simple step in the complete detailing of a vehicle, but as we will see, it is a very important one.


The purpose of the prep wash is simply to prepare the vehicle exterior for detailing procedures — like waxing and paint correction — 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 (like tar) and surface contamination but will get most of the loose stuff off so as to clear the way for the use of other detailing chemicals that can remove the 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. A thorough prep wash will actually help to save time in the overall detail process.


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 type of approach tends to be very efficient, given that it is accomplished 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 the car through the tunnel. Nonetheless, you may need to spend some time pre-tunnel applying extra cleaning agents to the front grill, wheels, and wheel wells.

Be aware also that the automatic car wash typically does not remove as much of the surface contamination that a thorough hand wash does. So you may have to spend a bit of 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, 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 coming off of these areas will splash onto the “cleaner” areas, so it makes sense to wash the cleaner areas last.

Even the most careful wash, using the best available tools and chemicals, will cause some micro-scratches in
the paint. Fortunately, use of good tools and chemicals will reduce such micro scratching to an almost unnoticeable quantity. Nonetheless, it cannot be denied that after repeated washing, a car’s paint surface (especially dark colors) will show accumulations of washing scratches, sometimes called “cobwebs.” Using the procedures described herein will help to greatly reduce such accumulations.

Most agree that the prep wash begins with an initial vehicle rinse-off, which will take off the loose dirt and dust, thus reducing the amount of scratching that occurs while continuing the 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 spit onto the remainder of the vehicle. So 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.

However, 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. For example, a common problem is bug splatters on the front exposures of the vehicle; a bug sponge or scrub block will work best for this.

As you clean the “lower third,” make your way around the vehicle, working 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 third 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. The wash mitt should have its own dedicated bucket of car wash shampoo. Change the solution in the bucket often to reduce the amount of grit that might accumulate from previous washes. If the wash mitt is dropped on the ground, it should be thoroughly rinsed to remove any sand or grit before being returned to use. Utilize a good, stable step stool for larger vehicles and a soft truck brush with a telescoping handle. Then rinse the vehicle thoroughly.

If your detail procedure includes removing environmental fallout, this might be good time to do so. Environmental fallout is a broad term that describes any contamination on the surface of the paint that does not come off with normal washing. It’s what makes the paint surface feel “gritty” or rough, even after thorough washing and drying. Most environmental fallout can be safely removed using detailer’s clay or a surface prep towel/pad while the car is still wet in the wash bay.

When the surface contaminant is paint overspray, it is sometimes better to perform the removal process after the car has been washed and dried. This allows for easier monitoring of the working area, which can ensure that all of the contamination is removed.

Another example of surface contamination is industrial fallout, sometimes called “rail dust” or a ferrous oxide deposit, which is basically tiny pieces of iron that are stuck to the paint surface. Light concentrations of industrial fallout can be removed with detailer’s clay or a surface prep towel. Heavier concentrations of industrial fallout will likely require a more aggressive approach. The approach of choice for most operators is to use oxalic acid washing procedures in the wash bay.

At this point, you can use detailer’s clay or a surface prep towel 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.

Upon completion of surface contamination procedures in the car wash bay, give the car a final rinse, top-to-bottom.
Some technicians prefer to dress a cleaned engine compartment at this point in the prep wash, so that the dressing can be sprayed across the entire engine bay without worrying about overspray getting onto the fenders and bumpers. Such dressing overspray would be removed while the vehicle was dried. Make sure to use non-silicone, water-based dressing for the engine compartment. Silicone can contaminate and disable some vehicle sensors. Solvent-based dressings are flammable and might ignite while operating the vehicle as the engine and exhaust manifold heat up.

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.


The prep wash should be distinguished from the “full service wash.” A full service wash is just that: a car wash without any surface contamination removal, paint correction, or waxing. Many of the stronger chemicals used in the prep wash will not be used for a full service wash because these stronger chemicals can strip away the protective chemicals (like waxes and sealants) that may be on the vehicle.

Instead, use a car wash shampoo that contains “wax.” This will give the car a few days of protection as well as adding to the gloss. Although using “car wash shampoo with wax” is not a substitute for the multi-month protection offered by standard waxing procedures, it does tend to leave a better look than straight car shampoo.


The prep wash, at first glance, seems like it should be a fairly straightforward process. But as you can see by this discussion, there are actually several issues and variables that make it a complex project. The most important thing to accomplish in regard to the prep wash is to set up standard operating procedures so that it 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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