If the tile

First of all, you should prepare the surface — clean it of dust dirt. If there are already tiles on the walls, it must be knocked down-for this it is best to use a punch with a nozzle-lobe (in the absence of a perforator, you can perform this operation using a hammer and a chisel). Then you need to align all the irregularities of the walls with the help of plaster. If the tile is placed on the floor, it can be leveled using a special solution. Check the level of surface level. It should be remembered that the permissible tilt of the wall or floor should not be more than half a centimeter.