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Orange Peel as it Applies to C4 Corvette Paint Quality

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Orange Peel:  A paint surface with a texture of "hills and valleys" similar to the skin of an orange. Excessive orange peel is considered a paint defect. It can be reduced by sanding, compounding, and polishing.

- Definition by 3M Corporation

Dan Stauft was a Paint Process Engineer at the Corvette manufacturing facility in Bowling Green, Kentucky back in October of 1995. At that time, he was a member of the ZR-1 Net - an online group of Corvette enthusiasts dedicated to the 1990 - 1995 ZR-1 Corvettes. A common complaint from many of the members was the amount of "orange peel" present in the 1984 - 1995 Corvette as compared to competitive European models. Dan was kind enough to offer the following explanation and we would like to thank him for his time in putting this response together:

The majority of Corvette complaints that I am aware of concern excessive Orange Peel relative to other manufacturers (i.e.) Lexus, Mazda, Porsche...). I would like to explain some of the causes of orange peel and a reason that US cars seem to have this problem more often than the other manufacturers.

Orange peel is the result of an applied coat of paint (basecoat, clearcoat, or both) that doesn't flow out or level fully. Keeping in mind that paint is basically applied as a liquified plastic, the cause of peel is that the paint either doesn't stay liquid long enough to completely flow or the material is to viscous to allow it to flow out. In either case, the paint ceases to flow before the surface is completely level. The result of this is a lumpy orlopey surface that resembles the peel of an orange, hence "orange peel. So, to eliminiate this problem, you lower the viscosity or simply keep the paint liquid longer, right? This may not be a s easy as it seems. Solvent-borne paints are categorized by the ratio of paint solids (resins, pigments, binders, etc.) to liquids (solvents).

1986 Corvette Paint ChipsIn the US, manufacturers are required to use high solids paints, with a ratio of about 60% solids to 40% solvent. To better flow the paint out, we need to add more solvent. The problem is that the EPA won't let us add aditional solvents. These solvent restrictins stem from the EPA's limits on Volatile Organic Compounds (VOCs). VOCs, which are in almost all solvents, are a cause of low level ozone - read smog - forcing these restrictions. In other countries, these restrictions either don't exist or are more lenient, allowing manufacturers to use low solids paints (as low as 30% solids to 70% solvent), which tend to have a smoother appearance. To combat the US handicap generated partially by EPA restrictions, paint companies are developing new technologies.

Waterborne paints, for example, are essentially low solids paints (up to 60% solvent), but they are legal because de-ionized water (not VOC) is a large part of the solvent package. In addition to the low solids aspect, waterborne paints have many other neat properties that help improve the performance and appearance.

As the new technology paints and application methods are implemented (within the next year or so for Corvette, US manufacturers will have the ability to level the appearance playing field between themselves and the international competition.

Dan Stauft
Paint Process Engineer
GM Bowling Green Assembly