A knockdown structure and assembly method are provided so as to prevent cracking of the sealant, reinforce the junction between sections, and improve the livability of the structure. A structure's body is assembled by using a mortar-powder mixed adhesive to join together a plurality of sections that are made of foam polystyrene and that constitute the parts of a structure having a predetermined shape. The adhesive is applied to cover at least the places where the sections are joined together with a woven inorganic-fiber mesh sheet. A sealant is applied, made by dispersing inorganic fiber and mortar powder in a plastic-type paint, onto the exterior and interior faces of the structure in a predetermined thickness. Onto the sealant of the exterior of the structure is applied, on the exterior of the structure, a paint that is water repellant and can screen out ultraviolet light, and applying, over the sealant of the interior of the structure, a clayey paint made of natural substances.