I. H. MURRAY Building Research Establishment, Scottish Laboratory


Loss of adhesion between render and brick is one major reason for the cause of rendering failure. Information is needed on the various factors which affect this bond in order to formulate simple and realistic guidelines for designers and contractors. The sorptivity of bricks from brickworks throughout Scotland was determined. Four bricks were then chosen to represent high to tow sorptivity. The moisture content of the surfaces to be rendered was varied and the adhesion of different render mix designs measured by a simple pull-off technique. Tests were also carried out on small walls (0.3 x 0.3 m) onto which render was applied. These walls had different pre-treatment before rendering. Differential movement was simulated by compressing the brick background only and measuring the strain in both brick and render until detachment occurred.