TILE BOOST will save tile setters time, frustration, and money by boosting thin mosaic tile out to plane (while keeping it super flat) AND boosting thick field tile up (allowing same-day tiling above the mosaic). And having the mosaic tile mortared tightly (with a V-notch trowel) to the Tile Boost avoids both sagging down and sagging in of tiny pieces. With small mosaic tile less mortar behind it is better.