PURPOSE: To keep a concrete slab completely out of humidity and securely perform ventilation and deaeration by providing bed adjusting boards on the waterproof bed and waterproof the bed with the adjusting boards.

CONSTITUTION: The principal ingredients of a bed adjusting board 7 are composed of blown asphalt, an asphalt felt and inorganic granules. The bed adjusting boards 7 are stuck and secured on concrete slabs 1 or an old waterproof layer 3. The bed adjusting boards 7 are also secured to a rising portion 6. The joint portions 13 are joined and put together with adhesive tape. If any bulged portion is found on the old waterproof layer 3, such portion is repaired by cutting and covered by bed adjusting boards 7 laid thereon. The bed boards 7 are stuck and secured to the old waterproof layer 3 either on the back side 7' thereof through rubber asphalt caulking 8 or on resin mortar provided on the old waterproof layer 3.