Should corrosion be visible it will appear in the form of a brownish-red for steel or white rust in the case of aluminum. This can be caused by contamination of the metal resulting from fingermarks, water, and so on, before the paint materials were applied. It can come from the original paint being removed by chipping off paint or leftover scratches, all leading to improper and inadequate pre-treatment of the metal surfaces. And with older hot rods, especially vintage tin, it can occur because rust wasn’t completely removed before proceeding or the new paint materials were contaminated at some point in the process.

To prevent corrosion from occurring, all metals need to be prepped with a metal treatment and a wash-primer. Make sure all chips and scratches are repaired before rust can set in and make sure to thoroughly clean area to be painted before applying any material. If you do spot water from the wet-sanding process on the surface, make sure to wipe it off and allow ample time to completely dry before proceeding.

If it’s too late and you need to remedy the problem, here are some methods: The paint will need to be stripped and sanded back to bare metal. (Bet you didn’t want to read this!) From here a metal conditioner and a phosphoric acid wash primer (you may be familiar with etch-primer) designed for your substrate (steel, aluminum). Once these steps are complete then it’s on to refinishing.


Often explained as a series of deep cracks resembling mud cracks in a dry pond usually manifested in the shape of three-legged stars and in no definite pattern, they are usually in the color coat and sometimes the undercoat as well.

The cause can occur from excessive film thickness, which magnifies the normal stresses and strains on paints, thus resulting in cracking even what would have been considered normal conditions. Other possible causes are materials not uniformly mixed, insufficient flash times between coats, incorrect use of additives, substrate is too hot or cold, the use of coats incompatible with each other, and lastly the omitting of the activator when mixing a 2K product.

So how does one go about fixing cracking? When applying a topcoat do not over apply material, allow sufficient flash and drying time between coats, do not fan dry by using compressed air from the spray gun (we’ve all seen this at one time or another), and make sure to properly stir (mix) all pigmented undercoats and topcoats. Additives not specifically designed for a color coat may weaken the final paint film and make it more sensitive to cracking. There’s also the obvious: Read and carefully follow recommendations in the Technical Data Sheet(s). These can be obtained from your paint supplier or from online.

To fix cracking once it has reared its ugly appearance you will need to sand to a smooth finish the affected area unless it is extreme cracking, in which case you will need to remove damaged materials and get to bare metal. From here a full refinish is necessary.

Edge Mapping, Shrinkage

We’re pretty sure most rodders are familiar with the term paint shrinkage but it is also known as edge mapping and featheredge splitting. It generally occurs as the result of “piling on” the undercoat in heavy and very wet coats. What happens is, solvent is trapped in the undercoat layers and have not had enough time to set up. It can also occur because the material isn’t properly mixed, especially with high pigment content of primer-surfacer; it’s possible for settling to occur after it has been thinned. Speaking of thinning, the incorrect use of thinner and reducer selection is another cause, as is improper surface cleaning. When not properly cleaned, primer-surfacer coats may crawl or draw away from the edge (shrinkage) because of poor wetting and adhesion. Another sure-fire way to screw up a good paintjob is to employ improper drying techniques. We mentioned earlier in this article about not fanning with a spray gun. Should this technique be employed after the primer-surfacer is applied it will dry before solvent or air from the lower layers is released. Another means to an edge mapping issue is the use of a too coarse of a finishing grit of sandpaper. This can occur when we try and save time, money, and/or our fingers! By skipping a step and not continuing on with the proper grit of finishing sandpaper is another way to create a problem.

The way to prevent this from happing is to properly apply reduced primer-surfacer in thin to medium coats following the prescribed flash time between coats. (Again, look at the data sheets for this info or ask your paint supplier.) Make sure to thoroughly stir all pigmented undercoats and topcoats, select only thinners/reducers that are recommended for the type of conditions you are painting within, and thoroughly clean areas (the shop as well as the surface area) to be painted before sanding. Make sure to use the recommended sandpaper grit before applying polyesters or undercoats.

Should you find yourself in trouble and need to remedy the problem now that it has occurred you will need to thoroughly dry off the surface area, sand, and refinish.

Environmental Contamination

A pair of long words for everyday occurrences attacking your paintjob; acid rain, bird droppings, spotting, pitting, acid marks, blistering, and insect marks. The discolored spots reside in the topcoat and are noticeable by the clearcoat losing transparency and/or its gloss. You will, in most cases, be able to see etching marks visible in the topcoat (probably the clearcoat).

Should you find yourself living in an agricultural area you car’s paint will be subjected to horticultural sprays as well as other regional or even seasonal bird and/or insect populations. The organic etching is accelerated by intensified sunlight (heat), while time and temperature dramatically increases concentration of acid. The damage is more visible on dark or darker colors due to heat absorption. Acid rain is the term given to rain containing effluents from manufacturing, chemical industries, and particularly power stations. Some of the effluents may be acidic or alkaline in the presence of water (e.g. sulphur dioxide will dissolve in water to give an acidic solution; even a mixture of cement dust and water is strongly alkaline).

To attempt to prevent this contamination the answer is obvious but not always feasible. Avoid the contaminated atmosphere. Get out the ol’ water bucket and wash your hot rod (or family car) paints often. After washing it’s always a good idea to protect your car’s paint/clearcoat (topcoat) to use a quality polish or wax; one that doesn’t contain silicone. Should you see the contamination, such as bird droppings, immediately clean with a mild detergent soap (or a car wash solution from a car wax manufacturer) before etching begins.

Should you find the contamination has begun the process then you will need to wash your hot rod (or family car) thoroughly with a water/detergent solution using a soft bristle brush and lightly scrub; keep the brush saturated with water. Afterward go over the affected areas with a rubbing compound and then follow with a proper polishing. Should the contamination be severe you may need to sand the affected areas, making sure the craters are sanded away completely before using a primer and topcoat.