INDUSTRIAL FALLOUT-PAINT DAM. FINESSE TYPE REPAIRS

SUBJECT: INDUSTRIAL FALLOUT/RAIL DUST DAMAGE TO BASE COAT/CLEAR COAT PAINT (FINESSE TYPE REPAIRS)

VEHICLES AFFECTED: 1992 AND PREVIOUS MODELS --------------------

The following information regards the use of finesse type repairs to environmental (industrial fallout) and rail dust damage of base coat/clear coat paint finishes.

Since the severity of the condition varies from area to area, PROPER DIAGNOSIS of the damage extent is CRITICAL TO THE SUCCESS OF REPAIRS. Diagnosis should be performed under high intensity fluorescent lighting, on horizontal surfaces (hood, roof, decklid) after they have been properly cleaned.

INDUSTRIAL FALLOUT (ACID RAIN)

There are three basic types of acid rain damage: - Surface level contamination, - may be repaired by simply washing the vehicle, cleaning the surface with a wax and grease remover, neutralizing acidic residue and finesse polishing. - Clearcoat etching, - slight etching still noticeable after the above washing and finesse polishing procedure. - Basecoat etching, - severe etching beyond the clearcoat into the basecoat.

PROCEDURES FOR SURFACE LEVEL CONTAMINATION REPAIRS

1. Wash the vehicle with standard car detergent and water and dry thoroughly.

2. Clean the affected area with a wax and grease remover. 3. Neutralize any left over acidic residue by cleaning the damaged areas with a mixture of baking soda and water (one tablespoon per quart of water), rinse THOROUGHLY and dry the panels completely.

4. Apply a finesse type polish with a foam pad.

CLEAN AND INSPECT THE SURFACE

A. If the damage has been repaired, remove any swirl marks with a dual action orbital polisher and foam pad. B. If some damage remains, proceed to step 5.

SLIGHT CLEARCOAT DAMAGE - WET SANDING, FINESSE POLISHING

5. Select a small test area on a damaged panel.

6. Wet sand the damaged area with an American Grade ultra fine sandpaper of 1,500 to 2,000 grit and a rubber sponge sanding block. During the wet sand process; a. Use ample amounts of water b. Go slow to prevent removing too much clearcoat.

Note: Be sure to use American Sandpaper. European Sandpaper has a "P" before the grit number and European grits do not align with American grits the majority of the time.

7. Remove the excess water with a rubber squeegee and inspect the area. A. If this has repaired the damage, continue the sanding procedure on the entire panel, apply a finesse type polish with a foam pad and remove any swirl marks with a dual action orbital polisher and foam pad. B. If (during the repair) it is suspected or observed that; - etching has penetrated into the basecoat OR - too much clearcoat has been removed during sanding OR - base color is transferred to pad during polishing,

THE AFFECTED AREAS MAY REQUIRE RECLEARCOATING/COLOURCOATING OR REFINISHING.

8. In any case, once the proper repairs have been made, the final step in the repair process involves polishing the vehicle.

A WORD ABOUT CLEARCOAT THICKNESS

The clearcoat on the vehicle is typically 1.5 to 2.0 mils thick (one mil equals .001" or 1/1,000 of an inch). At least one mil thickness is required to provide lasting protection to the vehicle basecoat.

PAINT GAUGES

The best way to accurately measure how much clearcoat has been removed is to use a paint gauge before, during and after the sanding process. Paint gages measure the total thickness of the finish and when used, can determine how much clearcoat has been removed during the repair process. Paint gages range from magnetic pull types to sophisticated electronic types, are available from a variety of sources, and can cost from $30 to $1800.

The older magnetic type gages, at best, a +/- 5% accuracy range and are not sensitive enough to detect removal of .5 mil clearcoat. The newer type magnetic gages have improved accuracy ranges. Most gages are confined to checking either a ferrous metal (steel) or non-ferrous metal (aluminum) panels. At this time, there are no viable gages for reading film thickness on non-metallic panels.

A more sophisticated gauge is the digital Elcometer 300 fn Paint Thickness gauge (or equivalent). It has an ability to read film thickness on both ferrous and non-ferrous metal panels. This instrument has an accuracy range of +/- 1% and has thickness standards included for recalibration. Approximate cost = $1750.

An alternative (for use on steel panels only) would be the digital Elcometer 246 model, or equivalent. This gauge has a +/- 3% accuracy range and include thickness standards for recalibration. Approximate cost - $575.

REPAIRING RAIL DUST DAMAGE

Rail dust damage comes from the tiny iron particles produced from the friction between the train wheels and the track. It can also be deposited on vehicles if stored near any operation producing iron dust (steel ore yards, etc.). This dust can either lay on top of, or embed into the paint surface. It is usually diagnosed as; - bumps in the paint surface OR - rust colored spots in the paint.

PROCEDURE:

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1. Wash the vehicle with soap and water, dry it and clean the affected area with wax and grease remover.

2. Keeping the vehicle in a cool or shaded area, rinse the surface with cold water.

CAUTION:

RAIL DUST REMOVER (OXALIC ACID) IS AN ACIDIC SUBSTANCE CONTAINING -------- CHEMICALS THAT WILL BREAK DOWN THE IRON PARTICLES EMBEDDED IN THE FINISH. WHEN WORKING WITH IT, USE THE NECESSARY SAFETY EQUIPMENT, INCLUDING GLOVES AND GOGGLES. FOLLOW THE MANUFACTURER'S DIRECTIONS CLOSELY BECAUSE IT MAY REQUIRE SPECIAL HANDLING AND DISPOSAL.

3. Soak several terry cloth towels in a container of rail dust remover solution and, after the damaged areas have been rinsed with cold water, lay the wet towels on the damaged areas.

4. Allow the towels to remain in place for 20 minutes, keeping them moist by spraying with water and not allowing to dry on the surface of the vehicle.

5. After 20 minutes of applying the towels, remove them and rinse the area thoroughly with cold water. Inspect the affected area to ensure the dust has been removed. Use both touch (feeling for bumpy surface) and sight (magnifying glass for close inspection).

6. If, upon inspection, some particles are still present, the process of applying the towels can be repeated 3 times.

7. Select a test area and hand wet sand with American ultra fine 1,500 grit to 2,000 grit sandpaper to repair damage (surface pitting from dust). a. Use ample amounts of water. b. Go slow to prevent removing too much clearcoat.

NOTICE - USE A PAINT GAUGE TO DETERMINE THE AMOUNT OF CLEARCOAT REMOVED. IF TOO MUCH HAS BEEN REMOVED, ADDITIONAL CLEARCOAT WILL HAVE TO BE APPLIED.

IF RAIL DUST HAS PENETRATED INTO THE BASECOAT, THE PANEL REQUIRES REFINISHING. MAKE SURE ALL RAIL DUST HAS BEEN REMOVED PRIOR TO REFINISHING OR THE RUST SPOTS WILL RETURN, CAUSING CUSTOMER COMEBACKS.

8. If the damage has been repaired, complete the repair to the entire panel.

9. Once the damage has been repaired, the final step in the repair process involves polishing the vehicle.

PREVENTING INDUSTRIAL FALLOUT DAMAGE

Customers should be urged to wash and dry their vehicles frequently and garage them, or at least cover them with a quality car cover when not in use.

Vehicles in dealer inventories should be kept clean and dry. A vehicle that sits unattended, especially after the sun has dried any water on the body surface, is a target for acid rain damage.

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.