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Water Vs. Solvent

Even picking the material to paint your car with is no longer easy, but it's not hard to understand

By , Photography by Courtesy Of PPG

No one wants to harm the environment, not even the most hard-core Bow Tie nut. We do our best to keep our Chevys running right, disposing of the nastier aspects of our hobby in the most environmentally safe and friendly ways possible.

When it comes to painting a car, the quest for environmental cleanliness has had dramatic effects, right down to the materials used. Lacquer-based paints gave way to solvent-based paints, which have now given way to water-based, or waterborne, paints. The methods of spraying paint have changed too, with higher filtration and HVLP (high-velocity low-pressure) paint guns helping to reduce the amount of airborne contaminants released into the atmosphere.

For our Project XS '70 Chevelle, we went to the folks at PPG for the paint and related materials to spray our ragtop in its two-tone red and black hue. In North Carolina, where Classic Automotive Restoration Specialists is based, spraying solvent-based paint is still allowed, so we went with materials from PPG's long standing Deltron line. But during the process we got to thinking, what about our readers in California and other areas where the environmental laws are more, shall we say, inflexible?

California is one of several states that has outlawed solvent-based paints in automotive use. This has required a serious adjustment for automotive painters, several of whom had become so used to spraying solvent-based hues that they could almost mix it in their sleep. Waterborne paint has been in the works for about 20 years, but only in recent years has it come to the forefront because of tighter environmental laws.

How does waterborne paint compare to solvent-based? Is one better than the other?

To find out more, we talked with Tom Place, the PPG rep who helped us pick out the materials for Project XS. He gave us the lowdown on some of the differences between the two paint bases, and some of the misconceptions people have of each one.

When you're painting a car from start to finish (starting with bare steel through primer, color, and clearcoat) there's very little difference in the application of both materials. Primers and epoxy sealers (referred to as substrates) in either application are still solvent based, because these materials already meet the tougher environmental rules for airborne pollution. Where waterborne comes in is the application of actual color to a car.

There are two basic types of waterborne paint. One is solvent-based, a "Band-Aid" version that helps shops comply with the tougher EPA rules. PPG's waterborne paint lines, Aquabase Plus and Envirobase, are fully water-based latex paints that meet EPA requirements but provide more stable materials for painters to use.

Waterborne paint is a heavier-viscosity material that covers differently from solvent-based paint. In an application of three coats, where solvent will spray on at a thickness of about 2-3 mil, waterborne will spray three coats of coverage in about half a mil thickness. This difference has an advantage when it comes to spraying a car in multiple hues or one with stripes. Because it covers in a thinner application, it takes less application of clearcoat to even out the surface because of the different layers.

A disadvantage is waterborne is much more sensitive to what's underneath it. If the bodywork and paint prep isn't near perfect, any imperfections will show up almost instantly because of the thinner mil thickness. Air line filtration is also critical. Any contaminants in the air lines will show up worse after spraying than with solvent-based paint.

Another aspect of waterborne is its sensitivity to humidity. We know you're saying "well, duh!" right now, but it's not as obvious as you'd think. The lower the humidity, the faster waterborne paint dries. Like with any paint, too fast a dry time affects the overall result.

For its waterborne lines, PPG has developed different versions for the different environments around the country. The mixture used by a shop in Florida, where the relative humidity is fairly high, is different from that used by a shop in Arizona, where humidity is almost nonexistent.

Airflow is another critical factor when it comes to waterborne paint. For optimal dry-through, an ideal paint booth will flow about 200 feet per minute of air. When it comes to airflow, waterborne and solvent-based paint share a lot of the same aspects when it comes to airflow sensitivities though.

When painting with waterborne paint, when wet it will tend to have a different hue from its true color. At first this can freak out an inexperienced painter. Once it dries though, the waterborne paint will take on its true hue. An interesting thing when it comes to the actual color with waterborne is that it comes out cleaner/brighter than a solvent-based paint.

Another interesting advantage of waterborne paint is the lack of leeway for painters to go into "mad scientist" mode when mixing in the thinner for final spraying of the paint. Currently there is only one thinner for use with waterborne paint, opposed to several different recipes used by painters for solvent-based. How a paint is thinned for spraying can greatly affect how it turns out, and each painter has his/her own method/recipes for thinning.

In the end, you can't say that one medium is better than the other. It's more about a different way of doing things. With ever tightening restrictions on airborne solvents of all sorts, it won't be long before other states adopt waterborne-only paint laws. As that time comes, waterborne will continue to be developed by companies like PPG, and much like how lacquer was replaced by solvent-based paint, waterborne will replace solvent, and everyone will adapt and learn how to create the same masterful paintjobs.

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