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I just had my mini sandblasted last year for a frame-off
rebuild, and have a couple of comments to make:
If you are doing a full restoration and want a strong bodyshell, then
sandblasting the entire bodyshell is a MUST. It will show areas that appeared
strong metal but are actually quite thin since "surface" rust can slowly weaken
panels. I had this problem with the floors which looked very strong and
relatively rust free. but once sandblasted, showed several small pinholes. This
means that the panels were weak, and just welding the spots would only delay the
ultimate deterioration. Naturally, you can only estimate the REAL cost of
restoring the shell AFTER the sandblasting. Since a frame off restoration is a
lot of work, I prefer to make sure that the basic structure is as sound as
possible. Note that when I started, there were only TWO small rust blisters
visible on the "A" panels, one on each side - NO penetration. Blasting showed
weakness in the scuttles, hinge panels, floors, step panels and rockers as well
as a small area ahead of the rear wheel arches. Now I am confident that Toybox
will not need any major work for another 20 years (1976 Mini)
We chose to chemically strip the shell BEFORE sandblasting. It took about 2 days
to complete, but this removed most of the paint and primer. So afterwards, the
sandblasting was mostly to clean the metal, and remove paint in the hard to
reach areas. This approach minimizes the amount of blasting needing done, which
minimizes the chance of panel damage Removing several layers of paint and
primers (and bodyfillers?) can take a lot of blasting.
Try to use a relatively "soft" sandblasting material like glass bead, fine sand
or walnut shells. This may help minimize the erosion/abrasion of the panels.
Beware some "industrial" shops since they might use very high pressure equipment
which may be more than is needed. Make sure the shop has experience with
bodyshells.
It will take quite an effort to make sure all the sand dust is removed from your
shell. Make sure that you air blast all the small nooks and crannies, or else
this sand dust may appear when you start painting. Naturally, this dust will
make quite a mess. A good clean-up is critical.
You must prime the shell as soon as possible, though I don't think that it has
to be immediate if you are working in a nice dry garage. After all, you will
probably have to do panel replacements and weld repairs before the priming and
painting. I used zinc chromate first followed by epoxy on the bottom and zinc
chromate and urethane primer on the top side.
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