Cementitious slab and means and method for forming same with lines of weakness

Claim 1

THE METHOD OF FORMING A LINE OF WEAKNESS IN A MONOLITHIC BUILDING FLOOR OR OTHER LOAD-SUPPORTING SLAB OF CEMENTITIOUS MATERIAL WHICH METHOD COMPRISES INITIALLY AT LEAST SUBSTANTIALLY LEVELING THE SURFACE OF A SLAB-FORM BODY OF FRESHLY POURED WET SOFT PLASTIC CEMENTITIOUS MATERIAL; THEN IMPRESSING INTO THE SLAB MATERIAL WHILE SOFT A JOINT MEMBER EMBODYING AN UPWARDLY PRESENTED CHANNEL HAVING A VERTICALLY MOVABLE WEB PERMANENTLY IN SERVICE PROJECTING FROM SAID CHANNEL ALONG THE LENGTH THEREOF IN SLIDABLE TELESCOPIC ENGAGEMENT THEREWITH, SAID JOINT MEMBER BEING IMPRESSED INTO SAID SOFT SLAB BODY MATERIAL TO COMPLETELY SUBMERGE SAID CHANNEL TOGETHER WITH THE LOWER PORTION OF SAID WEB IN SAID SLAB BODY MATERIAL WITH THE UPPER MARGINAL PORTION OF SAID WEB PROJECTING ABOVE THE LEVELED UPPER SURFACE OF SAID SLAB BODY; SUBSEQUENTLY DEPRESSING SAID WEB INTO SAID CHANNEL, WHILE MAINTAINING CONTACT WITH BOTH SIDES OF THE LATTER, TO ALIGN ITS UPPER WEB EDGE WITH THE SURFACE OF THE SLAB BODY AND THEN ALLOWING THE CEMENTITIOUS MATERIAL OF THE SLAB TO HARDEN WITH THE CHANNEL AND WEB PERMANENTLY IMBEDDED THEREIN TO FROM A LINE OF WEAKNESS IN SAID SLAB ALONG THE PLANE OF SAID JOINT MEMBER.