To effectively prevent seal cutoff of a joint formed by a construction ceramic based wail material 1 and facilitate construction.

An elastic string-like solid joint sealing material 6 having a sectionally easy-to expand shape is fitted into a joint portion in the way of shrinking its width after sealing adhesive 5 is applied thereto, so that the joint sealing material 6 easily follows a joint width, if spread by the shrinkage of a wall material in future, joint cutoff is avoided and the entry of water or others is prevented. In addition, sealing agent is solidified for easier handling and more simple construction.