Removing old
car paint
by Jim Ker
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 my 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 fiberglass can be soda blasted. Glass
is polished by the process and stainless and chrome trim retain their
luster.
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.
Not everything can be
cleaned with abrasives. Chemical strippers can be used in some areas
but there is always the problem of waste disposal, fumes and getting
the chemical out of body seams where it can later seep out and damage
a new paint finish. Even for the Pro's, some of the work has to be
done by hand. Wire brushes, sandpaper and elbow grease are all part of
stripping a project.
A project car always looks
really bad when it is all stripped. Fortunately, everything from now
on is aimed at putting it back together for others to admire.
Jim Kerr is a master
automotive mechanic and teaches automotive technology. He has been
writing automotive articles for fifteen years for newspapers and
magazines in Canada and the United States, and is a member of the
Automotive Journalist's Association of Canada (AJAC).
