My favorite DIY project is tiling floors, because tile comes in so many colors and textures and can completely transform the look of a room.
RedGard uncoupling mat membrane is ideal for installing ceramic or stone tile over challenging substrates, such as young concrete or plywood subfloors. It provides a waterproof and vapor-proof barrier and helps prevent cracks in tile and grout by absorbing the stress.
It is available at The Home Depot.