CHECKING CLEAR COAT THICKNESS BEFORE & AFTER PAINT FINESSE

IMPORTANCE OF CHECKING CLEAR COAT THICKNESS BEFORE AND AFTER PAINT FINESSE OPERATIONS - ALL VEHICLES WITH BASE/CLEAR COAT PAINT(Section No. 10-1)

Finesse procedures such as polishing or removing minor imperfections (refer to the Service Guild article in the February 1988 issue on page 45 titled "Polishing Techniques for Base/Clear Coat Finishes", the Service Guild article in the March 1988 issue on page 62 titled "Removal of Chemical Spotting and Other Minor Paint Imperfections Without Repainting, and Service Alert Video 89-6) may result in a lowering of the clearcoat protective film below the level necessary to provide minimum durability and performance requirements. As time progresses, a severe "whitening:" or degradation of the clearcoat may occur when clearcoat is removed below the minimum GM specification.

Oldsmobile recommends a paint thickness gage be used to determine how much of the clearcoat has been removed by the polishing or compounding process. Readings of the paint film build should be taken prior to the finesse operation. As the finesse operation progresses, additional readings should be taken to determine the impact on the total film build. If the gage indicates the total thickness has been reduced by 0.5 mils, it will be necessary to re- spray clear paint on the repair area to restore the needed ultraviolet protection. If the basecoat is disturbed, a complete repainting process is required.

There are many types of paint thickness gages available to the refinisher in today's market. The older magnetic-type gages, the best of which have a + /- 5% accuracy range, are not always sensitive enough to detect a 0.5 mil removal of clearcoat. Most gages are confined to checking either a ferrous substrate (steel), or a non-ferrous metal substrate (such as the aluminum hood, roof panel, and deck lid on some vehicles). At this time, there is no viable gage for reading film thickness on a non-metallic substrate (such as plastic or rubber).

Engineering recommends the digital Elcometer 300 FN paint thickness gage, or equivalent, for its ability to read film thickness on both ferrous and non- ferrous metal substrates. With thickness standards included for calibration purposes, this instrument is capable of reading film thickness within an accuracy range of + /- 1%. The approximate cost of the unit is $1750.00.

As an alternative unit for the refinisher who deals only with traditional steel components, engineering recommends the digital Elcometer 246 model, or equivalent. The gage demonstrates a +/- 3% accuracy range and comes with thickness standards for calibration. The approximate cost of this unit is $575.00.

Other digital paint thickness gages which demonstrate the same accuracy levels as the recommended Elcometer model are available from the suppliers listed below:

Elcometer, Inc. 1893 Rochester Ind. Drive Rochester Hills, MI 48309 (800) 521-0635 or (313) 651-0500

Defelsko Corp Zorelco, Ltd/Zormco 410 Cedar Street 8520 Garfield Road Ogdensburg, NY 13669 Cleveland, OH 44125 (800) 267-0607 or (216) 441-6102 (613) 925 5987

We believe these sources, their equipment, and materials to be reliable. There may be additional manufacturers of such materials and equipment. General Motors does not endorse, indicate any preference for, or assume responsibility for the products or equipment from these firms or for any such items which may be available from other sources.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.