I used spray foam on egg crate that was laying on a piece of acrylic (to provide a flat smooth surface on the back), then let it cure for a day. Then smear silicone over the whole thing, and press in aragonite. I tried 3 different kinds of sand on mine, and liked the roughest one the best. Then I saw greeneyedgirl's foam wall with aragonite, and I like it better. Looks a lot more natural. Then pop the egg crate off the acrylic and put it in place. Mine was cut to fit, and it pushed into place pretty tight. Then we siliconed around the edges just to be extra sure.