in the mid-1990’s, with the use of “self-consolidating concrete” (SCC), of which it is also a key ingredient.īesides the differences with concrete, self-leveling overlays also differ significantly from self-leveling “underlays”. Polycarboxylate was introduced into the U.S. One of the main superplasticizers used in self-leveling overlays is a polymer called, "polycarboxylate". The plasticizers used in self-leveling overlays, however, are more complex than those typically used in coatings, rubber and concrete, and are usually referred to as “superplasticizers”. Lastly, self-leveling overlays contain flow modifiers, or “plasticizers”, that help them spread out quickly, and level on their own, when poured onto a floor, and therefore require minimal finishing. Self-leveling overlays also use twice as much of these cements as the 10-15% Portland cement composition normally found in concrete, and they use higher quality fine aggregates to give the final surface a smoother and more consistent appearance. In addition, because self-leveling overlays don’t contain medium- or large-sized aggregate, like gravel or stone, which is a significant source of the overall strength of concrete, they make up for this through the use of special, “engineered” cements, such as calcium aluminate, that are much harder, and set up much faster, than traditional Portland cement. The polymer additive also gives cement overlay material greater flexibility - or “flexural strength” (something concrete doesn’t have much of either) - so that it doesn’t crack. This is commonly referred to as “tensile strength”. This polymer additive helps the cement in the overlay material hold together much better and not crumble like ordinary concrete would if it was placed so thinly. The reason self-leveling overlays can be placed so thinly is they contain a polymer additive, such as vinyl acetate or polyacrylic ester, that gives them greater cohesive strength than concrete. Unlike concrete, which is normally placed at thicknesses of 4” or 6” for a flooring slab in a new home or business, self-leveling overlays are put down very thin - most of the time between ¼” and ½” - and they do not noticeably change the elevation of the existing subfloor. However, that’s where the similarity between concrete and self-leveling overlays generally ends. Similar to concrete, self-leveling overlays also contain fine aggregate, like silica or quartz may contain pozzolans, like fly ash or slag come in gray or white and are mixed with water. Once dry, a self-leveling overlay can be covered with a traditional flooring material, like carpet, tile, hardwood or laminate or it can be sealed, and left exposed, to use as a wear surface, because its cement composition gives it a hardness and durability meeting or exceeding that of normal concrete. In essence, a “self-leveling overlay” is a cement-based compound, similar to a thick coating, like epoxy, that goes down over an existing concrete (or wood) subfloor to create a new, hard, durable and extremely flat, flooring surface. But they are also beginning to be used more earnestly with newer decorative options, such as polished concrete and concrete countertops. Self-leveling overlays have been around for around 30 years, now, and they are routinely used with decorative concrete flooring, for example, in acid staining, and with waxes and clear sealers. That, coupled with the fact that self-leveling overlays continue to expand in use with decorative concrete flooring, makes this an important issue. However, based on the number of inquiries we receive about self-leveling overlays, it is clear to us that, while many people may not know what self-leveling overlays are, they do realize they might be able to use one on a flooring project for their home or business. Most people, even in construction, remodeling and flooring, have probably never heard the term, “self-leveling overlay” - let alone similar terms, like “self-leveler”, “floor leveler” or “concrete leveler”.
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