Adhesion of new concrete to old depends on a number of factors, including sur~ face preparation, mechanical compatibility of the two concretes, temperature of the concrete substrate, and ambient temperature conditions at the time the new concrete is placed. Successful bonding also depends on the care exercised in placing the fresh concrete. Some practitioners and building product manufacturers promote the use of bonding agents to augment the bond at the interface. These products reportedly increase adhesion by enhancing wetting and sealing of the concrete substrate, thereby minimizing water loss from the fresh concrete to the substrate. Whether bonding agents effectively improve adhesion bas been debated. Some practitioners contend that they are too often used as substitutes for good concurring conditions and varying fresh concrete slumps.