Abstract: The invention relates to a two-part insertion member for use in the production of contraction or warping joints in continuously laid concrete slabs. The insertion member comprises a rigid lower part (to act as crack-inducing fillet) and a flexible upper part (to act as a sealing member) connected together, the lower part including an upstanding section which extends close to the uppermost extremity of the member. The invention also includes a method of forming sealed joints in concrete slabs.