We're placing a cementitious topping on an industrial floor, and the specifications require an epoxy bonding agent. The bonding agent must be wet or tacky when the topping is placed. After placing the bonding agent on a section of the floor, our mixer broke down and the epoxy dried. Can we reapply the same bonding agent over the section that has dried? If so, what sort of surface preparation is required?
If you apply a second coat of the bonding agent soon after the first coat has dried, you shouldn't have a problem. Just make sure that the dried epoxy surface is clean. If, however, you wait more than a day or so, most epoxy bonding agents will develop an amine blush on the surface. The amine blush feels oily and will prevent bonding of the subsequent epoxy coat. In this case, you should clean the dried epoxy with a solvent such as acetone or toluene, then apply the second coat after the solvent has evaporated. If the second epoxy coating dries before you are able to place the topping, you should seriously consider removing the bonding agent and starting over. Thick bonding agent layers are more likely to cause delamination of the topping due to differing thermal and structural movements between the epoxy and concrete.