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Picture perfect concrete polishing

After more than two decades, this memorable line from the movie The Karate Kid still illustrates how you can get a deeper understanding of repetitive tasks...

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After more than two decades, this memorable line from the movie The Karate Kid still illustrates how you can get a deeper understanding of repetitive tasks if you pay close attention to what you are doing. Here, Jim Sullivan, senior territory manager at surface preparation specialist National Flooring Equipment, explains how Mister Miyagi’s karate advice helps contractors avoid making costly mistakes when polishing floors.

From concrete cleaning and leveling to removing coatings such as urethane, epoxy paint or mastic - polishing floors is a progressive process that changes and refines an existing surface to a desired finish. But polishing is also gradual and meticulous, so when contractors don’t understand it fully or try to hurry it, costly errors happen. Below are some guidance notes to ensure your floor polishing projects are as smooth as possible.

The important first step

The first common mistake contractors and builders make in floor polishing projects is not preparing for the first steps well enough.

Preparing concrete floors involves multiple stages of grinding and polishing pads. Generally, contractors start with the coarsest diamond grit sequence. Each successive diamond grit sequence is smoother than the last, and removes removes the scratch pattern from the previous grit. This process ensures that the end result is a beautifully polished surface that does not show the scratch marks form the diamonds. Polished concrete floors are particularly popular in light industrial, commercial and residential spaces because of their aesthetic and highly durable nature.

Grinding involves the rotation of abrasive tooling attached to one or more disks. While the disks are rotating, the grinder applies down pressure at right angles to the surface of the floor. Grinding uses various types of diamond tooling attachments, carbides and resin bond pads to remove irregularities and achieve a consistent Concrete Surface Profile (CSP).

As a general rule, the grinding stage consists of any bonded abrasive diamond between 40 and 100-grit resin. A ground concrete surface has a flat appearance and no reflection. The grinding process is followed by the honing stage, which uses diamond tooling within the 100 and 400-grit range. Honing gives concrete surfaces a matte appearance and reflection. Finally, the polishing stage refers to anything above 400-grit and results in the concrete surface taking on a clear reflection and a glass-like finish.

Every step in the grinding, honing and polishing stages is important, but the most crucial one is the first step because it involves grinding high and low spots and opening up the pores of the concrete. This means the worker should run the grinder at a slow pace and often in two different directions to ensure the surface is perfectly even before moving on to the next steps. If the worker hurries the first step, the entire project may be compromised.

One step at a time

A flooring contractor will determine the grit sequence depending on the desired end result. Each step creates a smaller scratch and takes out the previous, larger scratches.

Another useful tip is to use a dust collector to clean any dust or residue from the concrete in between the steps.

It’s important for each step to take out the scratch from the previous step. Otherwise, the large scratches will still be visible at the end of the polishing process and the final result will not look very pleasing.

Know your scratch patterns

A good polishing contractor should be able to recognize the scratch patterns associated with different grits. This is where training, experience and craftsmanship combine to achieve the desired result on a consistent basis.

Best practice dictates the polishing contractor should inspect the diamond tool and carefully check the scratch pattern of every step in the process to achieve maximum refinement of the concrete surface before moving on to the next grit. If the technician fails to do these two things, he could easily go through all the steps of the process, but still not achieve the expected result.

This step is often overlooked and misunderstood, but the reality is that attention to detail when inspecting the scratch pattern can make or break a concrete polishing project.


Once the contractors finish the grinding work involving metal-bonded diamond, they should correctly apply a chemical hardener to densify the concrete. Densifiers are used to harden the concrete substrate, making the concrete easier to polish, creating a high gloss finish and improving the overall performance and durability of the floor.

Most densifiers consist of lithium, potassium or sodium silicate. When the silicate in the densifier interacts with the calcium hydroxide of the concrete substrate, it creates a crystalline surface, which adds strength and abrasion resistance to the concrete, allowing the polishing technician to achieve maximum refinement in the polishing stage.

It is important to follow the manufacturer recommendations for the time the densifier needs to be left on the concrete. This ensures the polishing phase will result in a much deeper shine.

Take your time

In some cases, a smaller machine could be more useful because it allows a careful inspection of each step and scratch pattern. Another option is to use two smaller, less expensive machines instead of a larger one. A passive planetary floor preparation system, such as National Flooring Equipment’s patented 8274-4 machine, is excellent for hard to reach spaces and is easy to operate. The machine’s quick-change magnetic tooling ensures it is versatile enough to remove adhesives, high and low spots and prepare concrete and overlays for coatings.

Time and budget constraints wrongly rule the construction industry. However, for polishing projects, the ultimate requirement should be achieving the desired result, not minimizing the time or budget spent on the project. This is why taking your time and paying attention throughout the polishing process are the two most important things, alongside using good quality equipment.