For many years one of the biggest problems in the construction field has been the bonding of plastic concrete to hardened concrete. This problem crops up when new toppings are applied over old concrete floors or bridge decks and when general repair work is performed on broken or spalled concrete. The earliest solution to the problem was the use of a plain cement grout. Later the polyvinyl acetate lax and other latex type bonding agents came into being. Then came the epoxies. There are now many epoxy polysulfide alloy bonding compounds, as well as some recently developed epoxy systems, on the market which will cure under water. This they must be capable of doing when wet concrete is placed against them. A good epoxy mortar should meet the following criteria: (1) the fine aggregates must be thoroughly dry and properly graded. Some formulators furnish a three-component kit consisting of the resin, the curing system and the aggregate. (2) the grading should be obtained from the manufacturer of the epoxy resin system since the requirements will vary from manufacturer to manufacturer. In general, however, a fine aggregate of the crushed stone variety, i.e. having angular particle shape, will provide the best troweling surface. (3) The volume of sand that can be mixed with any of these epoxy bonding materials is again dependent upon the material and actual figures should be obtained form the manufacturer.