by Jim Kerr
Warm weather brings out classic cars, cruisers and hot rods again. Some of these cars are fully tricked out with suspension and engine modifications and wild paint schemes. Others are completely stock, preserving automotive history. All of these vehicles garner their share of oohs and ahs as they roll down the street, but what many people don’t realize is what some of these vehicles looked like during their rebuilding stages. Many of them looked absolutely terrible, and that is where my project car is right now.
Regular readers may remember I purchased a 1964 Impala coupe as a project last year. Over the winter, slow progress was made and now the car is stripped, with the body ready to be lifted off the frame. Like most 40 year-old cars, there has been wear and tear and some rust. Most of the body is sound but there are a couple rust spots to clean up and several layers of paint to deal with. The next step is to strip off the paint and rust and see what actually lies deep beneath the surface.
Sandblasting is a common method of stripping paint and rust off metal but it is often not the preferred method for automotive repair. There are several disadvantages to sandblasting. The first problem is that it can be hazardous to those doing the blasting. As the sand hits the metal surface it breaks down into crystalline silica. Typically, sandblasting sand has 70% Crystalline Silica and inhaling it can cause Silicosis, a dreadful lung disease. Blasting personnel need to wear bulky fresh air breathing hoods while sandblasting. A dust mask isn’t enough.
Another problem with sandblasting is that it can easily warp thin automotive sheet metal. Using fine sand and low air pressures will do the trick but up the air pressure and those good body panels can quickly become twisted junk.
There are two parts of my car that I will have sandblasted. The frame is a heavy chunk of metal that has lots of surface rust. Sandblasting works well here. Another area is inside the car on the floor pans. This area is unseen when the car is finished and slight warpage here is not noticeable. There is a small rust area on the rear floor pan and sandblasting this area will clean it up in readiness for welding in a replacement repair panel.
The outside of a 1964 Impala is made of long flat panels. Sandblasting these would be a recipe for disaster, so I am going another route – soda blasting.
Soda blasting is an environmentally friendly way of removing paint, dirt and other surface contaminants without damaging the surfaces being cleaned. It is non-abrasive so there is no heat build up that would warp body panels. Initially, Soda blasting was developed by New York State engineers looking for ways to clean and restore the Statue of Liberty. They had many concerns involving issues of the environment, waste disposal, and protection of the Statue of Liberty itself.
Soda blasting uses sodium bicarbonate similar to baking soda but with a larger particle. The particles are propelled by compressed air and when they hit an object they explode, releasing energy that cleans the material away. Air pressure can be varied from 20 psi for blasting soft materials to 120 psi for harder surfaces. Unlike sandblasting, the metal is not worn away. In fact even plastics and fibreglass can be soda blasted. Glass is polished by the process and stainless and chrome trim retain their lustre.
Another advantage of soda blasting is that it acts as a rust inhibitor, leaving a protective coating on metal surfaces. When the time arrives to paint the surface, the protective coating (soda) can be removed by an application of a vinegar/water mixture.
Finally, waste disposal is much easier with soda blasting. Sodium bicarbonate has a pH of 8.4 and can be disposed of in most wastewater treatment systems. It can be neutralized by either a vinegar/water solution or just water dilution. The only material that needs to be disposed of are the coatings removed, which can be separated by dissolving the blast media in water and the use of a filter or centrifuge to separate the coatings from the now dissolved soda.
The only disadvantages of soda blasting are that it does not remove rust and it can be difficult to remove all the soda from boxed or concealed body structure areas. One friend had the soda “bleed” out of his car every time it rained for several months after it was painted, so that is why I will use it only for the large outside panels.