Hi, Debbie. If the tub really is in good shape, sandblasting should not hurt it. If it is basically rusted through, yes, the sandblasting will make a hole. Your best defense against a problem is to find a sandblasting professional that knows what he is doing. Many people can do sandblasting but not everyone knows how to do it well. Your best bet is probably someone that does this industrially every day. And a pro might suggest glass bead blasting which is less abrasive than sand.