As we know the Contraction Principle in the Physics, the same as tiles. Keeping space between tiles can avoid the deformation problem because of contraction.

              Firstly, let’s look at some improper construction pictures:

              It looks ugly, right? Under this kind of situation, we have to lever up the tiles and buy them again. It is lucky if we can buy the same tiles. Even if we buy the same one, maybe they look the same as we bought before, but it will be little different after paving them. Some perfect pursuit person may not accept it and need pave them again from the beginning. It is suggest that during paving tiles, we need reserve mortar joint. Generally exterior wall tiles need reserve 3MM, antique tiles need 5-15MM.