Chris, if you can't do a wall shelf, you have only one alternative and that's to secure the floor. The easiest way to do that is to put two or four posts (depending on the joist spacing) in the crawl space to support the floor joists right under where the rack sits (so that the floor won't bounce, at least in that area!) You need to go into the crawl space and use some (rented) jacks to jack up the floor joists an inch or two, and then slip in some 4x4 posts under the joists (set on those little pre-cast concrete piers so the posts won't rot ;-) It's simpler than it sounds and works like a charm.
Setting something heavy like slate or stone on a floor that already bounces won't help.
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Setting something heavy like slate or stone on a floor that already bounces won't help.
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