Good point. In general, the more filler you have, the less shrinkage there is during curing. Once cured, the cross-linked molecules in a clear epoxy theoretically should keep their shape, but the reality is that the small amount of shrinking that occurs during curing puts the hardened resin under a certain amount of stress that will tend to relieve itself over long periods presenting as additional shrinkage.
Also a common mistake is thinking that epoxy that has set is nearly cured. Very often an epoxy that takes just a couple of hours to set will take a week before it's fully hard, and you don't want to be shooting it before then or it will be prone to loosening up and failing prematurely.
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