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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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