Many sand blasters aren't used to working on thin sheet metal.
They're used to working on stone and heavy iron. Cosequently they
use to coarse a sand, too high a pressure, and work one area too
long if it doesn't come clean right away. The problems with
coarse sand and high pressure is easy to understand. The concept
of working to long in one area isn't. It's like welding a seam
in sheet metal. You have to do it in short tacks, skip around,
and let things cool otherwise you warp the panels. Time is money,
and the less time they spend on it, the more money they make.
They don't want to work beyond the time estimate as then they
have to bill you more than what the estimate was and hear you
scream.
Blake
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