There are lots of people asking about Dustless Blasting lately. To be clear, dustless blasting uses crushed glass + water + a water additive. I am no expert on dustless, but as always, there is no magic.
We prefer to blast indoors in a blast booth. This allows us to completely clean a body shell and do the both sides of body panels, put it up in the air and do the underside, etc. In other words, we provide a complete media blast for someone doing a full restoration. Yes our customers usually disassemble most, if not all, of the car.
In my opinion, the benefit of dustless is they will come to you and provide you with an outside blast of the car. For someone that does not want to dis-assemble their car, I believe this is the biggest benefit.
Like the marketing behind soda blasting 15 years ago, Dustless is getting a lot of press as manufacturers of the systems promote selling it. Here are my opinions surrounding some of the hype of dustless blasting:
1) As noted here, the equipment / start up costs are high
2) It is marketed as "environmentally clean." Clarification: they are still blasting with a media (crushed glass, which is clean), but the car is still being stripped, meaning that all of that old material is going somewhere...now it is just mixed with water and going into the ground! It does make a mess.
3) It is not any cheaper and is frequently more expensive based on local quotes that I have seen.
4) You typically do not get a complete blast (inside, outside and underneath).
5) No warping. Where this may be true, there is a lot of misunderstanding about media blasting and metal warping. It is not because of how "cool" the process is. More on this below...
6) Metal profile: you want a slight profile for good adhesion...not a smooth surface!
...not a myth, but do you really want treated water seeping into all of your seams and panels?
Anyway, back to warping. As mentioned by someone in an early post, we do not blast at a high enough pressure with a large enough abrasive to create heat (black beauty [aka coal slag] at 150 psi will cause plenty of heat). I can stand on the opposite side of a panel being blasted and hold my hand on it... no heat. However, blasting the under side of a hood, underside of a trunk, underside of a roof can STILL CAUSE WARPING. So why can this happen on thinner metal (sheet metal)? It is caused by the abrasion of the metal which molecularly changes the metal. An even pass over the metal causes no reaction at low psi with a "soft media." However, if you do the underside of that same piece of sheet metal and it is not a consistent even pass (such as the "triangles" inside the frame work of the underside of a hood) it will cause these sections to "drop." Or if you blast right up to the underside of a roof frame, these frames will "ghost" into the sheet metal above it.
Therefore, we do not blast the "triangles" on the underside of a hood (we do the frame work only) and we don't blast right up to the roof frames...we stay back a few inches.
And yes, you need a LOT more air than you think! Here is a chart for reference:
Sorry for the long post...I hope this is helpful!