PURPOSE: To shorten the working period by making thrust parts removable so that at least two interengageable surface forming parts which can be assembled for forming a desired shape may be moved from a set settable material.

CONSTITUTION: A set of parts 1 for use in building is constituted of a plurality of surface forming parts 2 and 3 which can be assembled freely to form a desired shape in a set settable material and thrust parts 4. The thrust parts 4 which hold at least the interengageable surface forming parts 2 and 3 in an assembled position is made freely removable so that the parts 2 and 3 may be removed and, consequently, the desired shape may be left in the set settable material.