W. H. HARRISON Building Research Establishment.

Many changes in masonry materials, design and workmanship have taken place in the last hundred years. Wide variations in composition of materials and their use can be tolerated in terms of durability. Greater mobility of labour and materials can lead to improved materials and designs, satisfactory in one area, being incorrectly used in areas of more severe exposure. The effect of these changes on weatherability are reviewed and the risk of insufficient durability in the future considered, particularly with respect to mortar.