Masonry building materials are more or less permeable. Water is the most significant factor in building deterioration by capillary water penetration. Impregnation of masonry with water repellents particularly with silicone impregnants is the most successful method of protection of masonry from capillary water absorption. This thesis investigates the various impregnants available for low-cost buildings and measures their effectiveness. It also develops a new impregnant to consolidate mud brick and effect water repellency.