Polished concrete

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Polished concrete is a multi-step process where a concrete floor is mechanically ground, honed and polished with bonded abrasives in order to achieve a desired level of sheen or gloss.

The Concrete Polishing Process

Concrete polishing begins with floor preparation. During this process, the floor is inspected and cleared to remove all unnecessary materials that can damage both the floor and the grinding machines. Floor inspection also includes hardness testing. Before a floor can be polished, it must have a hardness reading of 4,000 psi or higher for best results.^[1] A reading below this measure means the floor is soft and can crack under pressure. The next step is the initial grinding. In this step, low grit diamonds (e.g. 16- to 20-grit) are used to grind down all uneven surface until the floor is flat.^[2]

The next step is patching. Normally, all concrete floors have cracks. Patching ensures that all cracks, pinholes, and micropits are covered with grout before the concrete polishing process continues. After patching comes floor hardening. This step is also called densifying. Densifiers make the concrete surface hard enough for grinding and polishing. Densifiers to achieve a minimum of 32 to 40 mpa (megapascal) before it can undergo grinding.^[3] Densifying solutions also seal the floor from problems like rebar expansion, mildew, and mold.

Once the floor is hard enough, the next step is honing. This process is needed to refine the hardened surface using finer abrasives (e.g. 200- to 400-grit resin). After honing, the next step is polishing. Here, the floor is polished with much finer grit in order to achieve the desired sheen level, such as matte, satin, semi-gloss, and high-gloss. In a matte finish, the objects reflected on the floor have a hazy appearance. In a satin finish, the reflection of objects have a low-luster appearance. A semi-gloss sheen would have easily-identifiable reflections. Side and overhead lighting will also be visible. A high-gloss sheen will have highly identifiable reflections of images. When viewed from different angles, the floor will appear to be wet.^[4]

Polished Concrete Densifiers

A concrete densifier is a solution used to penetrate into the concrete and create a chemical reaction to harden and dust-proof the surface. During concrete polishing, the surface is processed through a series of steps (in general a minimum of four grinding steps of processing is considered polished concrete) utilizing progressively finer grits of industrial diamonds bonded in metal, hybrid or resin to make diamond polishing pads.

Under certain circumstances polished concrete may be LEED approved.^[5]

Concrete is not considered polished before 1600 grit, and it is normally finished to either the 1600 or 3000+ grit level. Dyes designed for concrete polishing are often applied to add color to polished concrete as well as other options such as scoring, creating radial lines, grids, bands, borders, and other designs. Any grinding under 1600 grit is considered a honed floor.