Wood fillers aren't cheap. I used to feel like every month I was throwing down ten bucks for a new tub when my current one was still 75% full…just crusty.
Anyone else have this problem?
Now the way I keep my glaze and filler soft, is to store the tub or tube in individual ziplock baggies with a little water.
Adding a tablespoon of water to a ziplock bag helps keep the moisture in and prevents hardening.
I store my fillers inside and that also help to keep them pliable.
If you've got a tub of filler laying around that's already pretty crusty, try adding a little water to remoisten it.