The Full Monty: Cold, hard facts about paint stripping

Ask most body shops how often they strip a vehicle’s finish before making a repair and the answer is likely to be “practically never.”

Or, as Kevin Kemp, co-owner of Crown Collision Center in Gilbert, Ariz. puts it, “If the paint is checking, cracking or peeling, we’ll remove the finish, but that’s very rare. The only vehicles we have had to strip are some peelers on a truck fleet.”

Craig Admundson, blueprinter at Raymond’s Auto Body, St. Paul, Minn., puts it this way: “If it’s delaminating, we strip it, but that only occurs about one percent of the time. If it’s been painted three times, we’ll probably remove the finish. Otherwise we’ll just scuff it.”

Admundson points out that Raymond’s is a high-volume shop—12 vehicles a day—and therefore can’t afford to spend a lot of time on stripping paint.

That seems to be the attitude among most shops. Paint stripping is time consuming and almost always unnecessary. What’s more, as Admundson points out, “Insurance companies usually won’t pay for stripping, so the owner winds up paying.” And that, of course, does not make for great customer relations.

Admundson adds, “You have to remember that the factory paint will adhere to the surface better than anything we can apply. They can bake at a higher temperature, for one thing.”

The 12-mil Rule

Many shops follow the 12-mil rule—i.e., the total finish, after the repair should not exceed 12 mils. Kemp figures it this way: “We normally apply 4.5 mils on a basecoat-clearcoat and 5.5 mils if we’re doing a pearl. The factory finish is generally 3.5 to 4.5 mils and 5.5 on pearls, and some of the late model Lexus and Infinitis are getting up to 7.5 mils.”

An instructor for one major paint manufacturer agrees that the collision repair industry has generally adhered to the 12-mil rule. But that could be a mistake. “Most paint companies’ warranties require paint to be applied to the OEM finish or a bare substrate,” he says. (A quick check with several other paint companies confirmed that this is generally true.)

What’s more, he explains, some OEM finishes total more than 12 mils, depending on what goes into the finish, such as anti-chip coatings, flexible primers and powder coatings. “I just measured a Dodge Stratus and it has 14 mils,” he says.

I-CAR recommends partial or complete removal of the finish if any of the following conditions exist:

excessive film thickness
cracking or checking
blistering
peeling
unrepairable environmental damage

Methods of Removal

The three methods of removing the finish, in order of popularity in the collision repair industry, are: abrasives (sanding), chemical stripping and media blasting.

“How the finish is removed is more a matter of personal preference, but there are some things to take into consideration,” says Jerry Goodson, I-CAR technical writer.

Most shops seem to go with the old, reliable dual-action (DA) sander. Some vehicle makers recommend against the use of chemicals, and media blasting requires special equipment. That leaves sanding, which is inexpensive and won’t harm the surface unless the technician is too aggressive.

No matter which method is used, the repair area should be washed with soap and water, rinsed and wiped dry. Then you should clean the repair area with the wax and grease remover recommended by the paint maker. Finally, mask and protect the areas where paint is not to be removed.

Goodson notes that when using a chemical stripper, the technician should also remove any body filler. “The corrosive characteristics of chemical paint remover can be absorbed into the porous filler and lead to contamination of the metal substrate,” he explains.

If it’s a delamination problem on an older vehicle that doesn’t have a full-body anti-chip primer, then aerosol chemical strippers are effective, according to Daryl Porter, manager, paint steering team, service technical support for DaimlerChrysler. Older vehicle is the key word here, because, Porter says, “We’ve been applying the anti-chip primer for several years.” (If the vehicle does have an OEM anti-chip primer, Porter recommends media blasting or sanding.)

He notes that there are a number of such aerosol products on the market. “They’re not as aggressive as aircraft strippers, but they’re very effective. You can just back-tape the panel, apply the aerosol stripper, and 20 or 30 minutes later you can literally vacuum the paint off. Then you scuff sand the e-coat and prime and paint.”

At Crown Collision Center, Kevin Kemp uses chemicals only if he can remove the part. “That way, there’s no danger of another part being damaged by the chemical. If it’s a roof or another part that can’t be removed, we DA it.”

Neatness Counts

Craig Admundson agrees. He also notes that neatness counts. “If you use a chemical, don’t let it run into jambs or holes. For instance, if you remove a hood scoop, be sure to mask up the holes. Same with door handle holes. You have to be really neat.”

Chemical stripping has the advantage of being less labor intensive than sanding. After the technician brushes on the stripper, he or she can go to another job while the stripper does its work.

Media—It’s a Blast

Media blasting is rarely employed by body shops because it requires special equipment and, often, a containment room for the operation. The abrasive, especially if sand is used, also creates a significant amount of waste that must be disposed of. That’s why when a shop does opt for media blasting the job is often outsourced.

Media blasting can be tricky, according to DaimlerChrysler’s Porter. “It depends on the equipment and the technician,” he says. “You don’t want to take the finish down to bare metal, you want to retain the e-coat. Some technicians just take it right down to metal. And some equipment is easier to control than others.”

Dry Ice, Anyone?

John Hughes, refinish paint specialist, Ford Custom Service Division, generally recommends plastic media blasting. “Aluminum oxide is only used for rust removal because it will remove phosphate metal coatings, causing flash rust from finger prints and humidity. Dry ice can also be used but facilities are limited.”

Did he say dry ice? Yes, he did. While media blasting is rarely used, dry ice is even rarer as the medium of choice. It does, however, offer a significant advantage: Because it converts directly from a solid blast pellet to a vapor (carbon dioxide), the media reclamation requirement normally associated with sand and wet-blasting systems is eliminated. That same advantage also removes the need for a containment room.

But, as noted, it’s expensive. To start with, there’s the equipment, which costs $10,000 to $30,000, according to Bob Foster, a marketing specialist for Coldjet, Inc. a supplier of dry ice for industrial purposes. “To use dry ice,” says Foster, “you need at least a 20-hp air compressor. The ice itself is 25 cents a pound and media blasting uses about two pounds a minute.” What’s more, he says, dry ice is not highly abrasive, so the operation may take longer than other media blasting methods.

This characteristic may be an advantage, however, in the rare instance where a shop is working on aircraft. The metallic skin of an airplane is thin and expensive to replace. The tiny dry ice particles will remove the paint, but leave the surface undamaged.

Yet another medium is sodium bicarbonate. That’s right, baking soda. While generally more generally more aggressive and less expensive than dry ice, soda blasting also requires specialized air preparation and blasting equipment.

Ford’s Hughes, however, is not a fan. “We don’t recommend sodium bicarbonate,” he says, “because you can’t clean it out of the pores of the metal well enough.”

Water is another option. Under pressures of 50,000 pounds per square inch, water will remove surface dirt, grime, grease and paint. But then the used water, contaminated as it is, becomes a waste problem.

Once the stripping step is complete, you need to inspect the surface to make sure all the finish is removed. Also check for the following: