another interesting thing about ashes when spreading them in water is that they don't float lightly on the water like you would expect. they sorta just dense up in one spot and begin to sink. the water turns dark and non-transparant. one must stir the water to get 'em moving. and there are an unexpected and startling number of bone fragments. those sink immediately, of course.
I wouldn't describe them as sandy though, more like heavy flour. a little denser than bread flour, but not grainy like corn meal, more like corn flour.