Bonding agents are used for cold joints and they distinctly improve the adhesion of the new concrete or mortar to old surface.

In several cases, wherein traditional repairs are executed by replastering gunniting, it is often seen that new concrete mortar mass separates from the old concrete. This obviously happens due to dissimilar behavior patterns of the old, already set concrete, and the subsequent new concrete which is undergoing stresses and strains while stiffening. Mainly due to shrinkages. In such a case, the use of bond coat between old and new concrete is the best solution.

Liquid epoxy in tacky condition is found to be an excellent bonding coat However, sometimes if a large area is to be concreted, the time lag between application of epoxy bond coat and subsequent placement of new concrete increases and it results in epoxy being partially or fully set and consequently separation cracks at the interface can be seen. This is not because of failure of the material but due to two pack epoxy not being utilized properly. Hence, use of user-friendly materials is necessary and this should preferably be a one-pack system.

Bonding polymers which are based on polymer latexes, when used along with cement give equally excellent adhesion both to old concrete as well as new one. There is substantial reduction in cost too and one pack nature of the polymer keeps the tackiness of the surface for a long time. It also helps to keep the conditions around the exposed steel and exposed concrete generally alkaline thereby preventing corrosion of steel and carbonation of adjacent and concrete. Pure acrylates, modified acrylates modified SBR and SBR are most commonly used for bonding purpose.