The increased surface area of tiles larger than about 8 x 8 in. makes it critical that you butter the back to ensure a strong bond. It takes only a few extra seconds per tile to spread a thin layer of thin-set on the back of the tile with the flat side of the trowel. Then when you set the tile, this thin layer bonds easily with the layer you've troweled onto the floor or wall and creates a strong connection. It's also a good idea to butter the back of larger transparent glass tiles to provid...