Abstract: A plug which fits into the top aperture of an air vent to be mounted on an air flow pipe or flume prevents cement flowing into the vent when a concrete floor is laid. The vent has a peripheral protrusion and a top flange. The plug protrusion snap fits into a in the top of the vent aperture and can be pulled out when the concrete is set. The plug has sides which extend upward an outward from the vent top so the laid concrete floor has a slot communicating with the vent and the vent top is installed below the floor and thus cannot be easily damaged by storing and removal of produce. The vent is inserted into a plate covering a flume where the plate has ribs and protrusions locating the required rebar and end tabs holding the plates end to end.

Abstract: A plug which fits into the top aperture of an air vent to be mounted on an air flow pipe or flume prevents cement flowing into the vent when a concrete floor is laid. The vent has a peripheral protrusion and a top flange. The plug protrusion snap fits into a in the top of the vent aperture and can be pulled out when the concrete is set. The plug has sides which extend upward an outward from the vent top so the laid concrete floor has a slot communicating with the vent and the vent top is installed below the floor and thus cannot be easily damaged by storing and removal of produce. The vent is inserted into a plate covering a flume where the plate has ribs and protrusions locating the required rebar and end tabs holding the plates end to end.

Abstract: Two slab bolster elements having rails supported on legs for carrying rebar during casting are connected end to end by a blade for sliding longitudinally of the rail into a female receptacle and a releasable locking mechanism which acts to lock the blade in the female receptacle. The locking mechanism comprises a notch on one side surface of the blade and a projecting portion of the female receptacle engaged into the notch. The projecting portion is carried on the female receptacle by a portion which can flex to cause the projecting portion to move away from the side surface of the blade. The female receptacle includes a manually depressible member on a side of the female receptacle opposite the projecting portion which when depressed provides motion toward the female receptacle which causes the projecting portion to move out of the notch.