Soda will remove any seam...
Soda will remove any seam sealer, undercoating, or body filler, which cuts way down on manual labor.
Original Corvette body components have a smooth resin finish without gelcoat, while aftermarket replacement panels are usually gelcoated. "Removing paint from gelcoat is easy to do without harming the gelcoat," Porter tells us. "It takes effort to remove gelcoat using soda. But the resin finish isn't as hard, and can be damaged with the baking-soda process if done improperly."
Sometimes cars have what Porter refers to as "rotten 'glass," and that can be a problem for soda blasters. "This is fiberglass that has deteriorated, possibly from previous chemical stripping where the chemical was left on too long, or sometimes [the fiberglass] just aged. The minute you blast that area, it looks like you blasted cardboard," Porter says. "Normal hand-sanding may not have brought this to light, and the area may have been painted over without anyone knowing it was bad. This would be an area that needs to be repaired, because it can affect the paint further down the road, resulting in a much more costly repair and repaint."
After the blasting process, a residue remains that acts as a natural rust inhibitor for steel, preventing flash-rust for long periods of time (depending on your regional humidity and proximity to the ocean, of course). While this coating is also on the fiberglass afterwards, its rust-inhibiting properties obviously don't come into play there.
The soda is blown through...
The soda is blown through a high-pressure hose, like a supercharged version of your home bead-blast cabinet.
It's this coating that has earned soda blasting a bad name. Soda has a pH value of 8.4, and it needs to be neutralized and washed away before the body can be painted. If the body isn't thoroughly washed, problems with paint adhesion will result down the road.
"The only thing soda blasting has against it is the reputation for paint lifting," Porter tells us, "but that comes down to human error, not the soda. Just like mixing and applying paint or body filler, there is a proper procedure that has to be followed to make the product work properly."
As a dust, the soda can be blown out with an air gun, but no matter how thorough you are, it will remain in really hard-to reach areas. It's water soluble, however, so a thorough power washing will completely dissolve any powder that remains. Initially, end users used straight water, or added vinegar or some other chemical to neutralize the soda, but it didn't get the job done (not to mention that vinegar and water would flash-rust metal pieces in hours).
The soda removes paint layers...
The soda removes paint layers pretty uniformly, showing the joint where seams were bonded. You can see the gray patch of factory plastic filler, and how it's lightly pitted. Unlike some other "soft" media, soda will remove plastic filler.
Soda Works, the equipment supplier Porter uses, recommends using a chemical called "Holdtight 102," a food-grade, environmentally friendly chemical that changes the surface tension of water "so it can microscopically remove contaminants from substrate," says Porter. It also contains a flash-rust inhibitor and salt remover. After power washing the car with the Holdtight solution, you have a 48-to-120-hour window to get steel pieces in primer before it starts to flash-rust; fiberglass doesn't require any other special care. Soda Works trains its technicians to thoroughly wash and neutralize the soda prior to giving the vehicle back to the customer. "Washing and neutralizing the vehicle should be part of the service for the customer," Porter adds.
It's been commonly written that soda blasters can remove one layer of paint at a time. "Well, I'm not going to say it can't be done, but it completely depends on the experience of the man doing the blasting, how much pressure he's using, and a variety of other factors," says Porter. In other words, don't plan on stripping a car down to its original paint.
Corvette-restoration specialist Alley Cats of Georgia has used NuTech to soda blast several Vettes over the years, and it was the shop's first choice when Mark Penk brought in his mother's unrestored '62, which she bought new. We were there while the team knocked the surface down until it looked fresh from the molds.