Heavy duty load wide inner leaf, for cavity widths 70-85mm to accept inner block width of 125-150mm. Lintels can then be propped to facilitate speed of construction and inner leaf block should not overhang the lintel flange by more than 25mm. Blockwork is built tight against the inner face of the lintel. Then place mortar bed on top of blockwork before floor units are laid to provide even distribution of load.