G.K. BOWLER*, P.J. JACKSON** and M.G. MONK*** * Hanson Brick, ** Sampling and Scientific Services, *** Blue Circle Cement

The incidence of water penetration of masonry subject to wind driven rain appears to have increased in recent years. Various factors have been blamed, including climate change, increased use of cavity insulation and, above all, workmanship. Traditional lime mortars were reputed to provide excellent workability and good sealing properties. This paper considers the role of mortar cohesivity in producing weathertight joints. Laboratory tests on small masonry panels have shown that different mortar compositions produce widely differing resistance to water penetration with the most cohesive mortars providing the best sealing properties.