PURPOSE: To prevent the cracking and water absorption of a joint and prevent the generation of mildew by forming an upper layer made of a caulking material added with no mildewproof agent or containing a half or below of the mildewproof agent of a lower layer on the lower layer made of a caulking material added with the mildewproof agent.

CONSTITUTION: Tiles 1 are stuck to a backing material 3, and a joint 4 is provided between the tiles 1, 1. A caulking agent added with a mildewproof agent is filled in the lower layer 5 of the joint 4. A caulking agent added with no mildewproof agent is filled in an upper layer 6. The mildewproof agent of the lower layer 5 is gradually shifted into the caulking agent of the upper layer 6, and a trace quantity of the mildewproof agent is contained in the caulking material of the upper layer 6. The generation of mildew is prevented, and discoloration can be prevented.