Is Waterborne Paint Better Than Solvent

Oct 27, 2023

Related Video

Painting a car is much like framing a house. Once paint hits the car, or those two-by-fours get up, the project feels almost done. Though that's not the case, paint is still a big step in any project, so we were really happy to finally be putting color on our '68 Camaro project, dubbed "Track Rat." Now, originally, we were going to cover the car in a satin finish, but we found that although the car would have looked great when first done, it would have been all downhill from there. Get a scuff, say from a poorly placed cone, and it's not like you can buff it out. The same problems arise from environmental contaminants such as bee pollen and gifts from our fine feathered friends. So, we wanted durability and that meant a traditional high-gloss finish.

There was a time when shops in California could still shoot solvent-based paints, but over time they were all forced to switch to waterborne paint systems. Like all new things, this change was met by most shops with apprehension. After all, most of the new "green" products out there might be better for planet Earth, but they tend to not work as well as their "dirtier" predecessors.

The truth is, waterborne paint isn't really new and the technology has been around a long time. Heck, Western Europe made the switch to water decades ago, and most new automobiles have waterborne basecoats. In the case of what we're using, Cromax Pro, it's Dupont/Axalta's third generation of waterborne paint.

There are two other things to note. First, today, only the basecoat is water-based. The primers, sealers, and clears are all just as they've been for a long time now: solvent based. The second tidbit of truth is that waterborne basecoats aren't all water. Water replaces a large portion of the solvents, but some solvent (about 10 percent) remains in the paint. This mixture of water and solvents acts as a carrier to move the "color" from the spray gun to the surface of the car. The water and solvents then evaporate, leaving behind the pigments and resins that give a car its color. The processes and techniques employed between the two systems are very similar; it's just that one sheds far fewer chemicals into the atmosphere. Specifically, water-based paints give off almost 90 percent less VOCs compared to solvent.

The main difference between solvent and water is how the two evaporate. The key with solvent is temperature, whereas water is driven more by humidity. Because of this, airflow is the key to faster drying times. The irony here is that the older cross-draft booths are better than the newer downdraft type. The reason is that as the water evaporates from the paint surface, the air molecules near the surface become saturated and can't hold more water, slowing the process. If air is kept moving across the surface that is drying, the saturated air is constantly being replaced with "fresh" air. The equipment needed to switch from solvent to waterborne paint is fairly minimal. Stainless-steel spray-guns are not optional, and fans can be used, but it really only speeds up the drying process. Also, make sure the compressed air is clean, since oil and water are known to not play nice together. The DuPont/Axalta paint we chose to use is also quite a bit different from other waterborne paints on the market. First, it uses a wet-on-wet process rather than the typical coat-flash-coat method. Second, it has a higher solid content (the color that's left behind once all the other stuff evaporates) of 20 percent, compared with 15 percent in other brands. This means that less paint has the ability to cover more car. Using less paint saves money on the supply side, and not having to wait for the paint to flash means money is saved on the labor side. Also, due to the higher solid content, coverage can be attained in as few as 1.5 coats, compared to the three to six coats needed with other paints. This results in a thinner film-coating that Axalta says makes Cromax Pro more resistant to stone chips.

Our painter, Jon Lindstrom of Best of Show Coachworks, was "forced" to make the switch to waterborne paint years ago. At first, the shop was a bit reluctant, but after working with the product they've found it superior to solvent based paints in many regards. They've also noticed that the colors seem more vibrant, which is a very good thing when you're shooting custom cars. The biggest issue is that it's somewhat harder to do repairs on older cars originally shot with solvent, since the waterborne paint shoots differently. But as time ticks by, and more shops move to waterborne paint technology, this will become as uncommon as coming across a car shot in lacquer.

With all the bodywork done, Jon Lindstrom did one final pass with 600-grit 3M paper. If the car wasn't going to get a sealer coat, then he would have used 800-grit.

All taped up and ready to go. One nice aspect of shooting a solid (i.e., non-metallic/pearl) is that panel orientation isn't critical, since we didn't need to worry about how the flake or pearl would lay down, or "flop." It also meant we didn't need to worry about shooting all the panels at the same time. Those other parts will be shot later, once we have the Chassisworks subframe back under the car and the panels in place so that we can lay down the graphics.

Before spraying, we made sure all of our seams were properly sealed with some Evercoat Maxim Flow Control. After all, it's not something we could do after painting.

In the paint booth, Jon used a lint-free towel and wiped the car down with some wax-and-grease remover.

The last step before grabbing the paint gun was to go over the Camaro with a DuPont Sontara Tack Cloth (PN E-4140). This helped to get the "bits and pieces" off the body of the car so we didn't end up contaminating the sealer.

The DuPont Premier Sealer is a three-part deal, and was mixed at a ratio of four parts sealer to one part Reactive Reducer and one part Activator Reducer.

DuPont has come up with a system for their sealers called value shading. The theory is that a color is described by three dimensions: hue, saturation, and value. Hue describes the dominant wavelength, or "color" (e.g., whether it is green, red, or blue); saturation describes the purity of the color or how much the color has been diluted with white; value, or tone, describes the brightness or darkness of the color. Value is the element of color that most controls the number of coats needed to achieve full coverage. The value shade for our particular color of blue turned out to be four.

By using a primer/sealer that is pigmented to the correct value (shades of gray, from light to dark) the number of coats needed can be greatly reduced, and less paint equates to a lower cost of materials. Even though this is less important with a high-solids, waterborne paint like Cromax Pro compared to solvent-borne systems, it still helps. Here, Jon lays down a nice coat of sealer on Track Rat. As always, he starts at the top and works his way down and around the car. For an in-depth, step-by-step guide to painting your car check out this story: www.motortrend.com/how-to/1504-1969-chevrolet-camaro-step-by-body-and-paint/

One common misconception about waterborne paint is that the whole "system" is water-based, and involves no solvent. This isn't the case. Only the actual color, or basecoat, is waterborne. The rest, such as the sealer and clear coat, are traditional solvent-based products. Still, shooting waterborne does require a stainless gun so the equipment doesn't develop rust. For this job, Jon busted out his Iwata stainless LPH400 gun. The orange tip is what he uses for base coats and sealers. Expect to pay between $400 and $500 for a gun of this caliber, and another $130 for the tip, or air cap.

When paint sits around, it can separate, with the pigments settling to the bottom of the can. Obviously this is bad, so we tossed our paint on the shaker to get it all mixed up proper-like. Our color was chosen from DuPont's Spectramaster Color Atlas and the code is CAS471. Now, be forewarned that the color you see on the little one-inch square may or may not look the same when it's covering an entire car.

The color we were trying to nab was one we saw on a '53 Porsche, which that company called Azure blue. Since we've been swamped, we didn't get a chance to do a spray-out panel before shooting the car. Let's just say we got really nervous when Jon started laying out the first coat of what looked like neon-aqua "Smurf" blue.

Waterborne paint is a lot different than solvent-based, though, in the way it changes shades as it dries. Here you can see the huge color difference between the wet area (the shiny part) and the drier area that is more matte. Cromax Pro utilizes a wet-on-wet application process. What this means is that there's no need to let the first coat of color "flash" before shooting subsequent coats. Also, due to a higher solids composition, you can achieve full hiding in as little as 1.5 coats. This saves money, since most painters typically lay down four or more coats of color when using solvent-based paints, and even some other kinds of waterborne paint. Even so, Jon laid down 2.5 full coats, just to be on the safe side.

With the basecoat color down, we let it dry for 15 minutes before moving onto the clearcoat. Now, the main difference between water and solvent is the way the carrier evaporates. With solvent, the evaporation rate is mainly driven by temperature. This is why there are a variety of reducers. High-temp reducers slow the evaporation rate down so that the paint doesn't "dry" too fast; low-temp reducers speed up the evaporation rate to make the paint dry faster when the temp drops. With water, the evaporation rate is driven by relative humidity and temperature. If the air is drier, the water leaves the paint film faster. Here "desert" controllers slow down evaporation when the air is very dry, and standard or high-humidity controllers speed up the process when the air is very humid. With waterborne paint, air movement is key, since still air becomes saturated and slows down the evaporation of the water.

While the color was drying in the booth Jon started mixing up the clear. The DuPont Premier Clear is a two-part system which is mixed at a ratio of three parts clear to one part activator.

After three heavy coats of clear, the body of our Camaro was looking good. This go-around, we only shot the body and doors. Later, we'll tackle the fenders and other parts, which will incorporate the graphics designed by Ben Hermance. After that, we can tackle color-sanding and buffing.

The paint is dry, and we can start getting ready to put on the Camaro's graphics along with painting the complicated pattern on the carbon-fiber hood. If you want to see the graphics story, click here.

Editor's note: This story was originally published July 25, 2013.