Craftsman Concrete Floors

Texas Concrete PolishinG 

Polished concrete floors are synonymous with modern luxury. Over the last decade, they’ve become one of the most prevalent flooring solutions for luxury home construction. One of the main attractions to polished concrete floors is the wide variety of achievable finishes. In new home construction, architects and designers specify many aspects of concrete floors, from the concrete mix and troweling of a new slab, to the grinding, finishing and polishing of a slab after it's cured. This article is an overview of these decisions. If you need assistance achieving the perfect finish for you new house, contact us for a consultation.

Polished concrete floors are installed by grinding a concrete slab multiple times with progressively finer diamond grinding tools. The first several steps are called ‘cutting’ and utilize aggressive grinding tools to remove imperfections, flatten and homogenize the surface of the floor. The number of cutting steps is a function of the desired finish and the quality of the concrete mix and pour. It's during this stage that stone aggregate in the concrete can be exposed. The final ‘polishing’ steps utilize less aggressive diamond tools and progressively increase the reflectivity of the concrete surface. The number of polishing steps is dependent on the desired level of reflectivity.

Concrete Mix

A 10% fly ash, cream polished Craftsman Concrete floor. The high fly ash content increases the depth of the natural design on the floor’s surface and allows for a highly reflective finish.

A 10% fly ash, cream polished Craftsman Concrete floor. The high fly ash content increases the depth of the natural design on the floor’s surface and allows for a highly reflective finish.

Color
In new construction, color is added directly to a concrete mix rather than as a stain after the slab has cured. This has many benefits over staining, most notably durability and consistency. Stained concrete floors have a tendency to discolor in high traffic areas, requiring touchups and maintenance. In new construction, color can be achieved by adding a pigment to or increasing the fly ash content of the concrete mix. Fly ash is a byproduct of coal combustion. This light-weight, anthracite colored particle is added as a filler to most concrete mixes as a way to increase the finished strength and hardness of a concrete slab. A standard concrete mix contains about 5% fly ash. Increasing the fly ash content of a slab will both darken and harden the finished floor. This can be beneficial for cream polishing, as harder floors will be more reflective and have ‘more depth’ in their finish than softer floors. Further, as the fly ash is a very small particle, it will separate in the top ‘cream’ layer of the concrete, giving an exotic marble finish to the floor.

Aggregate
Aggregates (rock and sand) are added to concrete to increase it’s finished strength and durability. In a typical concrete mix aggregates account for 60% to 75% of the volume of the concrete. Aggregates are much stronger than the other materials in concrete and serve to prevent cracking and deterioration. When concrete is poured and troweled the aggregate separates by size, with smaller sand and rock particles rising to the surface of the floor.

Aggregate is sourced from quarries, oceans, rivers, or crushed recycled materials. Aggregate can be specified for size, sharpness or roundness of edges, and color. For certain types of finishes, the choice of aggregate will have a dramatic impact on the appearance of a finished concrete floor. These finishes are ones where the surface of the concrete floor is ground off, exposing the aggregate to be polished. For salt and pepper exposures, where only sand and very small aggregate is desired, using ‘native’ or river rock is ideal as it’s rounded edges allow it to separate and sink in a concrete mix. This separation insures that only tiny rocks and sand are exposed at the surface of the floor. For floors with exposed aggregate, rocks with jagged edges and varying sizes will give a ‘tighter’ appearance to the floor. The jagged edges fit together like a puzzle, keeping the rocks suspended near the top of the concrete mix. For these types of floor, it’s ideal to have as much rock exposed as possible as aggregate will polish to a higher shine than the concrete in which it’s suspended. For polished concrete floors with exposed aggregate, the color and size of the aggregate is carefully selected to compliment the design of your home. In general, architects or interior designers will help a home owner determine what specifications will work best.

Troweling
For most applications, it’s ideal to power trowel a concrete slab, using pans under the power trowel’s blades. Pans will create the flattest floor possible, while effectively separating the concrete into layers and keeping the cream layer intact. For floors that will be finished to a cream polish, it’s essential that water isn’t hosed onto the slab to keep the slab workable. While this might allow for a flatter concrete floor, it may also wash the cream away as the floor is troweled.

Concrete Polishing

Small aggregate exposure ‘Class B” Craftsman Concrete Floor. Picture taken after cut but before polish. This floor’s dark color is due to it’s 10% fly ash content. The aggregate used is ‘native’ rock. Notice the bright colors and consistent exposure this rock facilitates.

Small aggregate exposure ‘Class B” Craftsman Concrete Floor. Picture taken after cut but before polish. This floor’s dark color is due to it’s 10% fly ash content. The aggregate used is ‘native’ rock. Notice the bright colors and consistent exposure this rock facilitates.

Cutting
For polished concrete floors where exposed aggregate is specified, the first finishing step is referred to as ‘cutting.’ For polished cream floors where the poured surface of the concrete is polished, the cutting step is skipped. Cutting is achieved by tooling composed of diamonds bonded in a metal matrix. This tooling is aggressive and designed to quickly and effectively remove the surface of a concrete slab. A typical cut is three steps, using tooling of 40, 80 and 120 grit.

Polished concrete floors are specified with different amounts of exposed aggregate. The Concrete Polishing Association of America classifies these levels from A to D, with D having the most aggregate exposed. Below is a chart containing these concrete polishing standards. Larger exposures of aggregate take significantly more time and skill to achieve, but offer breathtakingly modern finishes that are not achievable by any other method. At Craftsman Concrete Floors, we specialize in polishing floors for modern finishes, including large aggregate exposure.

CLASS EXPOSURE CUT DEPTH
A CREAM NONE
B SALT AND
PEPPER
1/16TH INCH
C SMALL ROCK 1/8TH INCH
D LARGE ROCK 1/4 INCH+

Polishing
The steps of the finishing process where a floor becomes reflective are referred to as the polishing steps. Polishing is executed by tooling composed of diamonds bonded in a plastic or resin. This tooling isn’t aggressive and is designed to modify only the surface of the floor. During the polishing steps, only a minimal amount of material is removed. A basic polish is four steps, using tooling of 100, 200, 400 and 800 grit. For the highest reflectivity possible, additional 1500 and 3000 grit steps may be added.

Reflectivity
Depending on application and taste, polished concrete floors are specified in four levels of reflectivity. The Concrete Polishing Association of America classifies these from 1 to 4, with 4 being the most reflective. Below is a chart containing these concrete polishing standards. Most residential applications specify level 3 and level 4 floors, with higher levels of reflectivity requiring significantly more skill to execute.

High clarity and reflectivity Craftsman Concrete floor with large river rock aggregate. After a heavy cut this floor was polished to a 3000 grit finish. Notice how clear and sharp reflected objects are.

High clarity and reflectivity Craftsman Concrete floor with large river rock aggregate. After a heavy cut this floor was polished to a 3000 grit finish. Notice how clear and sharp reflected objects are.

Low gloss “Class 1”, Large Aggregate Exposed ‘‘Class D” Craftsman Concrete Floor. The aggregate has been chosen for its jagged shape and gray color. Notice how tightly the rock is incorporated into the floor, creating a terrazzo style finish.

Low gloss “Class 1”, Large Aggregate Exposed ‘‘Class D” Craftsman Concrete Floor. The aggregate has been chosen for its jagged shape and gray color. Notice how tightly the rock is incorporated into the floor, creating a terrazzo style finish.

Image Clarity
Theres more to a high quality polished concrete finish than just reflectivity. Reflectivity measures the percentage of light that is reflected off of a concrete floor. More importantly for creating a beautiful polished concrete floor is clarity. Clarity is a function of floor flatness, density and porosity. Dense, nonporous, flat floors reflect an image like a mirror, without waves or distortion. In properly polished concrete floors, reflections will look sharp and clear without haze.

 

LEVEL GRIT APPEARANCE
1 100 Matte and non-reflective
2 100-400 Satin - Difusely reflects light.
3 800 Polished - Reflections can be identified.
4 1500+ Highly polished - Mirror like finish.