A joint former for hardenable material such as concrete comprises two essentially identical web members which are releasably attached to each other by a two-part friction coupling to form an assembly which is generally a T-shaped assembly. Each web is configured along at least one edge to form a first coupling part and along a central portion of at least one surface to form a second complementary coupling part so that any two of such webs can be attached to each other to provide a T-shaped assembly. In use the web forming the body of the T is inserted into the hardenable material, the bar web serving to align and position the inserted web. The bar web is then detached from the inserted web and releasably attached to another essentially identical web to form another T-shaped assembly suitable for use in the manner just described.