Synthetic latexes are made by dispersing polymer particles in water to form a polymer emulsion. When these emulsions are added to portland cement concrete, the spheres of polymer will coalesce or come together to form a film that coats the aggregate particles and the hydrating cement grains and seals off voids. The resulting mixture develops higher strength, bonds better to existing concrete, has a higher resistance to chloride penetration and is more resistant to chemical attack than plain concrete. The three basic polymers used as latex modifiers for concrete or mortar are acrylics, styrene-butadiene rubbers (SBR) and polyvinyl acetates (PVA). Defoamers are incorporated into the polymer emulsions when they are manufactured to inhibit formation of excessive air that would be caused by foam generated during mixture of the mortar or concrete.
To obtain a high bond between the latex concrete overlay or mortar patch and the base concrete, a bond coat is brushed or broomed onto the prepared concrete surface. This bond coat can be the mixture used for the overlay or patch, or may be made by mixing undiluted latex with portland cement.
A polymer film formed as a latex coalesces helps to maintain high levels of internal moisture in the concrete. Because of this, prolonged curing is neither necessary nor recommended. To prevent shrinkage cracking before the film has formed, however, all finishing operations must be completed and the surface covered with a single layer of wet burlap as soon as the surface will support it.
