Aggregate Exposure in Polished Concrete

The Concrete Finishing Process

In a typical concrete floor you will never see the aggregate that is added. The finishing process involved with new concrete flooring pushes the aggregate into the mix allowing the cement paste and water (cream) to rise to the surface so it will be a nice smooth floor. When choosing to grind the concrete we remove the cream layer which results in aggregate exposure (usually various sizes of stone and sand). This could result in variances and random exposure of varying degrees of exposed aggregate on the surface of the floor. This is the many reasons why achieving the correct floor flatness at the time of placement and finishing is critical.


The Make up of Concrete

The role of aggregate in the concrete is critical for key strength and the structure. Concrete is made up of cement powder, small aggregate, large aggregate and water. The concrete gets its strength from the water and cement powder acting as a glue that holds all the aggregate which makes it very hard in a fixed place.

The Depth of a Polished Surface

Choosing the depth of the polish determines the size of the aggregate in the final floor finish. The choice to expose the aggregate in a floor polish is completely cosmetic. Here are the various options.

Option 1- Cream Finish

This level of finish polishes the top layer of the concrete. This is the most affordable option and also provides the most color movement and shifting when using dyes or stains to color the concrete. This will show some of the tooling marks from the finish process of pouring the concrete. The finished floor has a lot of movement and shifting in the surface.

Option 2- Light Exposure

This level of finish exposes the sand and small parts of the larger aggregate. When using the aggressive diamond abrasives to remove glue or a sealer from the concrete, this is typically the finish unless deeper grinding is required. When staining this kind of floor, a more monochromatic color will be achieved.

Option 3- Heavy Exposure

This level of the finish really exposes the larger aggregate on the concrete surface. This gives the concrete more of a terrazzo look. This type of finish is usually the most expensive as it involves extensive grinding at the initial part of the concrete polishing project. When grinding this deep we recommend a grouting process to fill air voids and rock pop-outs in the concrete.

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