Embedding Powder in Resin Surface

Hi y’all,

I work for a campus research lab, and the project we’re on now heavily involves resin. Long story short, I need to embed a fine powder partway into a UV resin so that it stays there, even when the resin is placed underwater.

The method I’ve been using is to warm up the resin bottle in a water bath, fill a large (~8.5×11″) rectangular mold with as thin a layer as possible, cure it in a foil lined box for 3-4 min, sprinkle the powder on top with a sifter, and cure for another 10-12 min.

Sometimes the method works great, and after washing off the excess, the resin layer is quite tough underwater and doesn’t stick to itself. It has a leathery sort of texture, and can be re-used.

Lately, though, I can’t seem to recreate this. The resin is not well cured, and the back stays slimy. If I cure it longer to compensate, it becomes brittle and cracked. Even after rinsing off the extra and air drying, it remains very sticky, sticking to itself and its glass container.

Any thoughts on how to increase consistency in the process? What’s the right cure time to get the powder to stick, and the right secondary cure time to fully cure without cracking? What’s the right amount of resin to use to avoid liquid bottom side after unmolding? Any secret tips or tricks that might make my life easier?

Thanks a bunch.