Self-leveling concrete is polymer-modified cement that has high flow characteristics and, in contrast to traditional concrete, does not require the addition of excessive amounts of water for placement. Self-leveling concrete is typically used to create a flat and smooth surface with a compressive strength similar to or higher than that of traditional concrete prior to installing interior floor coverings. Self-leveling concrete has increased in popularity as the degree of flatness and smoothness required for floor covering products has increased, with vinyl goods becoming thinner and floor tiles becoming larger, for example.
The term self-leveling was coined in the United States by ARDEX, Inc. in 1978 in reference to their first self-leveling product, ARDEX K 15 Premium Self-Leveling Concrete Underlayment. The term was used to differentiate it from traditional concrete, which is typically stiffer and requires more labor to get it into place and finish with a trowel.
In the category of self-leveling concrete there are two main groups of materials: underlayments and toppings. Underlayments are installed over an existing subfloor to smooth it out and correct any surface irregularities prior to the installation of all types of floor coverings, including sheet vinyl, vinyl composition tile (VCT), wood, ceramic tile and carpet. Toppings perform a similar function but act as the actual finished floor without the need for a floor covering. Some typical applications for concrete toppings include warehouse floors, light industrial applications, retail stores and institutional facilities. Concrete toppings can also receive pigmented color dyes, stains, saw cuts or mechanical polishing to produce a decorative concrete finished wear surface.
When self-leveling concrete is poured, it has a viscosity similar to pancake batter. A gauge rake is used to move it into place without spreading it too thin. The finishing is then done by lightly breaking the surface tension of the product using a tool called a smoother. The polymers in the self-leveling mix keep the viscosity of the product such that it remains uniform in composition from top to bottom without the sand aggregates sinking to the bottom of the installed layer. The typical installation thickness of these products is about 0.25 inches to ensure there is enough mass present for the material to flow, although some self-leveling products now exist that can be installed at an average thickness of only 0.125 inches.