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, getting more information, or signing 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 paint correction and waxing — 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 and clear the way for the use of specialized 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. A thorough prep wash will actually contribute to time savings in the overall detail process.


In a facility that processes several vehicles a day, 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 left over 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 connected with an automatic car wash, don’t assume that the car wash tunnel will be sufficient to “prep the car for detailing.” An automatic car wash cannot substitute for the intricate manual brush work that is necessary to thoroughly clean doorjambs, front grills, wheels, and other areas.

As such, 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 onsite car wash. Still another approach is to pre-wash the dirtiest parts of the vehicle, like the engine bay, wheel wells and wheels, and doorjambs with a pressure washer, then run the vehicle through the automatic car wash.


If the detail job at hand includes work in the engine bay, wash the engine first. This falls into the notion of “wash the dirtiest parts of the vehicle first.” As you are blasting the engine with chemicals and rinse water, the rest of the vehicle is going to get sprayed with dirty, greasy water. So, it makes sense to get this done before proceeding with the prep wash.

Of course, if you are working on a relatively new vehicle that has mostly plastic covers across the top of the engine, it may be possible to simply wipe these off with a damp towel.

But in the case of a dusty, oily, greasy engine bay, the cleaning procedure is fairly straightforward. You may want to moisten the entire vehicle with a quick rinse. This will protect the rest of the car from staining in the event that some degreaser splashes on it. Then, as you work on the engine bay, be careful around electronics like fuse boxes, the alternator/generator, and after-market electronics like alarm systems. Otherwise, most engine and transmission components should be able to be carefully cleaned and rinsed without issue.

Rinse the engine bay first. If you are using a pressure washer, it is recommended to set the pressure somewhere between 800-1200 psi. Any more than this can cause damage and any less is not effective. Next, mist the engine bay with your favorite heavy-duty degreaser. It may be necessary to use some brushes to agitate some of the larger flat areas and grease accumulations on some components. Then perform a final rinse. Use compressed air or a leaf-blower style machine to blow off the excess water.

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.

From an operational standpoint, one of the issues with engine compartment cleaning is adherence to The Clean Water Act. The runoff from engine cleaning (and normal car washing) cannot be allowed to go into public storm drains that end up draining to a body of water. If you are in a fixed location, make sure the drains in your prep wash area actually go to the city’s water treatment plant. If you are cleaning engines on a mobile basis, you may have to use a wastewater containment system and reclaim the dirty rinse water for proper disposal.


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 “cob webs.” 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.

Then, work on the other typically dirty areas of the vehicle, like the doorjambs. 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 terrific soft-bristle 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; bug removing chemical, along with 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 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. Some technicians prefer to load the car with car wash shampoo using a foam cannon. The wash mitt should have its own dedicated bucket — with a dirt screen — 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.

Some technicians like to also have a second bucket (with a dirt screen) of plain water to rinse the wash mitt before reloading it with shampoo solution. Utilize a good, stable step stool for larger vehicles and a soft truck brush with a telescoping handle.

After washing the main body of the vehicle, rinse it thoroughly, from top-to-bottom.

Per your preference, dry the vehicle with chamois, squeegee, a large microfiber towel, or a combination of these. When using deionized water or water treated with reverse osmosis, it may be possible to let the vehicle drip-dry, saving some time on the physical drying step. Then blow out the seams and crevices with compressed air (not greater than 60 psi, please!) or a leaf-blowing type machine. The vehicle is now ready for further exterior detailing.


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. We will continue the prep wash discussion with some specialized procedures in next month’s column.

Prentice St. Clair is an International Detailing Association Recognized Trainer and Certified Detailer. As the president of Detail in Progress Inc., he has been providing training and consulting to car washes and detail shops since 1999. He is available at (619) 701-1100 or