Construction materials placed on this concrete fl oor when it was fresh affected hydration and left circles and lines that only showed up when acid stain was applied. To solve the problem, artisans covered the ruined fl oor with a microtopping, then applied amber-colored acid stain to get the look originally intended.
Photo courtesy of Concrete Solutions, Inc.

The Science of Slim: Polymer-Modified Toppings

Polymers aren’t as colorful as pigments, acids and other raw materials used in decorative concrete. But because they help thin cemetitious toppings hold together, they are just as important.

Decorative concrete is both an art and a science, and nowhere is that more true than in the case of thin overlays and toppings. The art lies in the palette of finishes and designs that make old, worn concrete look bright and new and different. The science lies in the chemistry that makes these toppings possible.

“Thin toppings” in this case means cementitious overlays applied at a depth of 1 inch or less — sometimes as thin as 1/16 inch — over an existing slab. While they have the look of regular concrete, they are not formulated in the same way. “Standard concrete has no strength at that depth,” explains George Henderson, president of PermaCrete/Quality Systems Inc. “It depends on its mass for strength, so it must be 2 inches thick, at least.”

Steve Crast, technical director for Crossfield Products, adds: “Traditional cementitious materials depend on alkali silica reactions and hydration of cement. Minimal thickness is difficult to achieve without shrinkage or cracking. Bonding is also a problem.”