Paint - Damage Due to Industrial Fallout or Acid Rain
88peugeot07BULLETIN NO. 314
DATE: November, 1988
SUBJECT: PAINT DAMAGE DUE TO INDUSTRIAL FALLOUT OR ACID RAIN
Acid Rain can damage paint in as little as several hours. "Industrial Fallout," either by itself or combined with dew, rain and sunlight, can also damage paint.
Although present-day clear coat oven-baked enamel paints, as used on most Peugeot vehicles, are the most resistant paints available today, they are however not immune to such damage.
In order to help you when customer complaints of paint damage are encountered, attached are pages describing:
- various types of paint damage from fallout and acid rain
- typical sources of each type of paint damage
- how to protect against paint damage
- how to repair some forms of paint damage
This information, supplied courtesy of DUPONT, may help you to track down a local source of pollution as well as be able to factually explain to customers why the paint on their vehicles is "damaged" and not "defective."
CHEMICAL SPOTTING OF AUTOMOTIVE FINISHES
1. What is chemical spotting?
Chemical spotting is a discoloration or disfigurement of a painted surface through the action of reactive chemical contaminants which fall on the paint surface from air borne mists and/or dusts.
Generally those contaminants that attack a paint film are either acidic or alkaline in nature (e.g., acid rain is a solution of a gas such as sulphur dioxide in water which acts like sulphuric acid; cement dust when mixed with water is very alkaline, forming a material which acts like caustic potash).
2. How is the painted surface affected?
One of two ways, or both. Generally the pigment of the paint film is attacked by the contaminant, causing all or part of the colors in the paint to be damaged.
For example, a red color made from a yellow and a maroon will increase in maroon color, leaving purple or deep red spots if the yellow part of the red pigmentation is attacked and bleached by the chemical contaminant.
However, some chemical fallout materials can mark or disfigure the resin part of the paint, turning it milky or dull. This will show up as light or white spots, or dull patchy low gloss spots.
3. What topcoat paints are affected?
All paints can be affected, however some are more resistant than others. In general, the most resistant paints used today are the polyurethanes whose resin system, because of its chemistry, is least likely to react with air contaminants.
Air Dry coatings are more susceptible to attack than baked coatings, particularly when the coatings are fresh. The longer they dry, the more resistant they become, but they will always have some propensity to chemical attack. The longer the chemical remains on the surface, the greater the chance it will mark or discolor the painted surface.
4. What paint colors are most susceptible to attack by chemical fallout?
In general, metallic colors are most susceptible to chemical attack. This is because of the aluminum flake used to provide the metallic effect. Aluminum is a fairly reactive material with either acids or alkali. However, some solid colors are also sensitive and, depending on the type and concentration of the contaminant and the length of time it remains in contact with the surface, they can also be affected.
Attached is a chart which shows some color groups and the effect of some chemicals on them when they have been left on the paint finish for 24 hours (Chart #1).
5. Sources of Chemical Fallout
Chemical fallout can come from industrial sources such as the effluent from stacks of manufacturing or processing facilities or oil/coal fired power plants. These sources may be nearby or many miles away, with their contaminants borne on the wind or released into the atmosphere where they are dissolved by moisture and returned in the form of rain.
The attached list gives possible sources of acid/alkaline contaminants based on industries that use these types of materials (Chart #2).
6. How to protect against Chemical Spotting:
A. Keeping car finish clean is a key to preventing chemical spotting, although it is not always noticeable when contaminants have deposited oil the car. A routine of a weekly thorough washing is important.
Thorough routine waxing of finishes will help to minimize chemical spotting, but will not guarantee freedom from chemical attack. This will depend largely on the type of chemical, its concentration, and the length of time it is on the surface.
B. Clear coating of cars can provide significant protection against chemical spotting by protecting the pigment from being discolored. However, the clear itself can be attacked by contaminants, leaving a dull or milky spot on the finish. Urethane clears tend to be the best for clear coat application.
C. Freshly painted cars are more susceptible to chemical spotting than aged paint jobs. In the first 2-3 months of a new paint job, care should be taken to regularly hose down the finish to remove accumulated contamination.
7. Repair of Chemical Spotting
Depending on the degree of chemical attack, polishing or compounding may remove the spots; however, if the chemical attack is severe, refinishing maybe necessary. In this case, the surface should be washed thoroughly with soap and water and followed with a wash with solvent designed to remove waxes, oils, and greases. Wet sand affected areas with #500 sandpaper. Re-clean car surfaces and mask car as required. Topcoat to nearest breakline using procedures appropriate to the topcoat label instructions.
To remove acid rain damage, start with the least aggressive procedures. "Finesse"* the area that is damaged. Lightly sand using 1200-3000 grit with water, then polish. After this operation you can decide if you need to proceed. The next step of course is to refinish. The use of water with baking soda or Lux soap and water may neutralize the acid or alkali before any operation is started.
* "Finessing" is a new polishing technique that enables many forms of paint damage to be successfully repaired ratlier than repainted.