I've been cleaning a lot of sand and gravel for aquariums (I had a couple of hundred once upon a time...), fill a bucket with sand and just dig down a water hose to the bottom. Let the water flow, when it's clear the sand is clean.
In the epoxy business we are very often "boosting". After 10-20 hours of curing, the object is heated to 100 degrees Celsius (it depends on the epoxy though) for another 20 hours. It raises the heat resistance and the mechanical properties very much.
Good luck with the experiments!