A. O’ROURKE The Nottingham Trent University

The maximum permissible V-value (thermal transmittance) for a wall is 0.45 W/m2K or 0.6 W/m2K if the trade off provision with double glazing is used. Since July 1995, the Building Regulations have required the inclusion of cold bridges, such as mortar joints, when determining the U-value of an element. As a result, many cavity wall constructions built with ultra-lightweight blocks will be in excess of the statutory requirement. A method of overcoming this problem is to specify a mortar that has a thermal conductivity value that is closer to that of the blocks. This paper outlines the development of a lightweight mortar containing expanded blast furnace slag. The thermal performance is compared with that of an equivalent traditional mortar and physical properties such as air content, flow, water retentivity, consistence retentivity and compressive strength are also compared. The results highlight the superior insulating qualities of the lightweight mortar and demonstrate that these can be achieved without affecting the compressive strength of the mrotar. The mortar mixes containing 100% Ebfs had the best overall performance.