Myth: blasting parts is the same as cleaning them.
Fact: blasting and washing are two very different processes, with very different results, and you cannot substitute one for the other.
I think social media may be (at least partly) to blame for the confusion. We’re always posting photos of rusty, paint-covered parts side-by-side with “cleaned-up” photos of the same part, stripped down to bare metal.
One looks dirty, and the other looks clean. And, in a sense, that’s partially true.
However, the Kaser blasting booth is not equipped to handle large amounts of oil and grime.
The blasting process is like a very concentrated version of what happens to your face when you’re at the beach on a windy day: you might lose a layer of skin to abrasion, but that’s not a substitute for washing your face in the shower.
We blast dry, using grit (crushed glass, aluminum oxide, or steel grit) powered by air. There’s no water or solvent involved. Since we reuse our blast medium several times, we can’t let it get contaminated with oil and grime, or it loses its effectiveness.
When parts come out of the blasting booth, they have a surface profile, or a sandpaper-like texture designed to grip the coating we’ll apply later on.
On the other hand, washing parts requires a piece of equipment aptly labeled a “parts washer,” or a little basin in which parts can soak in solvent. Solvent does a great job of cutting through oil, not unlike the way dish detergent cleans oil off of a pan.
After washing, we blow the parts dry with compressed air before taking them to the blasting booth. The solvent evaporates off of the part, leaving behind little to no residue. Other than removing oil and grime, the solvent does not affect the part’s surface in any way – you cannot achieve a surface profile through washing, so we don’t advise taking a part straight from the parts washer to the pretreatment booth.
When we’re dealing with a particularly oily part, such as the rear end of a car, washing and blasting are two sides of a coin: washing the part cuts through the oil, but not through the rust, nor does it impart the surface profile we need in order to coat the part effectively; blasting the part removes rust and old paint, and imparts a surface profile, but the blast medium will stick to the part if it’s oily, causing coating adhesion issues down the road.
In short, washing a part is not adequate preparation for coating, because it does not impart a surface profile. On the other hand, blasting is not a silver-bullet solution for cleaning oily parts. We often need washing and blasting in equal measure, to perform two very different functions.