FORD chemical deposition and its' effects on automotive finishes

The pH condition of a car's painted surface is critical to the appearance and ability to sell a new or used car. Acid rain, water marks and bird droppings have caused damage to automotive paint finishes costing car manufacturers many dollars in repairs and repaints. 

Environmental factors have played a role in these concerns. Basecoat/clear-coat paints were developed to help reduce the solvent emissions that low solids (high solvent) paints systems released as they cured.  However, the high solids resin system in clear-coats were not as chemically resistant as the older paint systems. At the same time, nitrous oxide and sulfur dioxide emissions from power plants, car exhaust and air pollution from industrial plants are now trapped in rain water and deposited on the new car finish. 

This acid rain is a very dilute form of nitric and sulfuric acids. The sun dries water droplets containing these acids; and, as the water evaporates, the acids concentrate. The concentrated acid then penetrates the clear-coat dissolving the resin and forming a pit. Left untreated, the concentrated acid can continue into the basecoat destroying the pigment. 

Bird droppings contain a byproduct called uric acid. This alkaline, if left non-neutralized, can penetrate the clear-coat and cause damage. 

Alkaline water marks are also a common paint problem on today's automotive finishes. Hard water spots are calcium and magnesium salts that deposit on the paint after the water has evaporated. These are white rings of minute crystals that bond to the paint. They are not re-dissolvable in water. Harsh detergents found in some car wash soaps contain sodium silicate or sodium hydroxide may etch the surface of the clear-coat leaving white residue or dulling the entire finish. 

The pH is the technical measurement of the acidity or alkalinity of aqueous solutions. The scale ranges from 0 to 14. A pH measurement of 7 is neutral (neither acid or alkali) which is the reading for distilled water. A pH reading from 0 to 6.99 is an acid while a solution that has a pH from 7.01 to 14 is alkaline. The following list shows the comparison of acid rain to common known chemicals and other household products. 

TYPICAL pH OF COMMON CHEMICALS

Currently, the paint manufacturers are developing clear-coat systems that are more resistant to environmental damage. However, knowledge of the pH condition of a car's paint surface will continue to be important for proper pre-treatment prior to paint sealing and to prevent damage to stored vehicles.