Solvent Popping
Solvent popping or boiling as it’s sometimes known can be recognized by groups of small bubbles or crater-like openings in the paint surface. This condition is often caused by solvent getting trapped in the paint film when it skims over before all the solvent is allowed to evaporate. The solvents left under the paint film rise up ultimately “popping” through the surface leaving pinholes or craters. This is caused by the paint film skinning over because either too fast a reducer/thinner was used, or there was excessive air movement over and around the vehicle that dried the surface before the before the buried solvents had time to evaporate. This situation can be fixed by allowing the effected area to dry or cure fully and then sanding and refinishing as needed, or if it’s severe you may have to strip the effected area and then prime, seal, and recoat as needed.

Discoloration
Discoloration, or bleed-through is a yellowish stain that appears in the topcoat over areas repaired using glazing putty or body filler. It’s usually caused by too much, or in the opposite, too little hardener in the putty or filler. It can also be caused by incomplete mixing of either, or from priming before the filler/putty is fully cured. In minor cases it may disappear as the topcoat fully cures, but normally you’ll have to sand, seal, and refinish the area. You can usually eliminate the bleed-through by making sure you don’t use excessive amounts of crème hardener, by mixing fillers or putty completely, or by sealing any repair areas before painting.

Blistering
Blistering, sometimes called pimples, are bubbles or swelled areas that show up in the paint surface weeks or months after a paint job. They’re caused by moisture that’s been trapped under the paint surface and is sometimes caused by spraying during really high humidity conditions. It can also be caused by contaminated air lines, failure to drain your compressor, or by painting over an unclean or contaminated surface. Blistering can sometimes be repaired by sanding the affected area and refinishing, but usually one has to actually strip the area to its bare substrate and start from scratch. This malady can be prevented by always draining your compressor and air lines, proper cleaning and prepping before painting, making sure everything is totally dry after wet sanding, and making sure you use the correct thinner/reducer for your spray conditions

Blushing
Blushing is a common problem when spraying in high humidity conditions. It happens when the air and evaporating solvent from the spray gun lowers the temperature of the surface being painted to below the dew point (the temperature at which air becomes saturated and produces water). This condition causes condensation in or on the paint layer producing a smokey or milky looking cloud on the paint surface. Blushing can normally be corrected by adding a bit of retarder (a slow evaporating solvent) to your paint mixture and then recoating, or by letting the finish cure and then compounding and buffing. You can help prevent blushing by using a good-quality thinner/reducer that’s correct for your conditions, adding the recommended amount of retarder when spraying in humid conditions, or by applying heat after application to help evaporate excess moisture.

Crazing
Crazing and cracking is a condition in which cracks (or lines) of different lengths and direction form in the finish. This is caused by excessive film thickness of either the topcoat or undercoat. It can also be caused by shooting over a previously crazed surface, using too much hardener in either your primer or paint, not thoroughly mixing your spray materials, or using off-brand or another brand of reducer or hardener in your mixture. The only way to correctly fix this paint problem is to strip the area and refinish it. You can usually prevent crazing by always following the material manufacturers label instructions, by always using a manufacturer’s complete line of products (no intermixing of different brands), and making sure you mix your coatings completely before spraying.

SOURCE
PPG
11276 5th St #500
Rancho Cucamonga
CA
http://www.ppg.com/coatings/refi
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