Development of a novel mortar for use with unfired clay bricks

Interest in traditional unfired clay building materials, including cob, earth brick, and rammed earth, has grown in the UK in recent years. Although the use of vernacular techniques, such as cob and rammed earth, has raised the profile of earthen architecture, a wider impact on modern construction is more likely to come from modern innovations such as unfired extruded clay masonry units and premixed plasters. Traditional unfired clay walls often have basal widths of 300 mm or more, providing an inherent stability and resistance to toppling through self-weight. Masonry units extracted from UK brick production lines before the firing process are typically 100 mm wide, which requires good mortar-brick bond strength to meet structural robustness requirements in a typical 2.4 m high wall. In testing, traditional mortars based on clay, cement or lime, have not provided sufficient strength. This paper examines the bonding of unfired clay units with unconventional mortars based on novel binders. It reports on the development of a mortar which appears to be suitable for a wide range of clay types. This mortar can be readily recycled and has a carbon footprint lower than many alternative binders. Results of long-term bond strengths and the structural performance of masonry walls are given, which demonstrate the suitability of this mortar for use with unfired clay masonry units.