Great idea. Thanks!Water down some white glue, paint it on where you want the texture, put on a bunch of baking soda and then when it's dry, rub it off. The remnants should be very fine. Very GENTLY drybrush.
clay based cat litter, I made some small sieves out of plastic pots (yoghurt pots would do) with different size holes in each, I can grade the cat litter from 'boulders' to 'fine sand'