Should Polished Concrete Crack?

The high school in my hometown is undergoing a major renovation. One of the new features is a poured concrete floor stained with a pattern and polished to look like terrazzo.

This popular flooring type is appearing in many facilities around the country. But according to the architect of the project, this floor could be expected to crack within the first year.

In our coverage of polished concrete floors, I have not heard of it cracking. Is this common? Is it supposed to happen?

  • I don't understand why it would crack if installed properly.
  • First off polished concrete is becoming a very common flooring choice. For reasons that make a whole bunch of sense, however, concrete is one of those installations that requires professional installations. Just like any other flooring choice that is available today. There are several variables when installing this flooring and anything that is skipped or overlooked can cause cracking to occur. Moisture content, thickness, curing time, and of course the support within the concrete. No, it is not supposed to crack. If it were, noone would choose it. Something went wrong during the installation, but it can be repaired. That's the good news.
  • I have never seen polished concrete flooring crack in a school or office setting. However i have experienced this problem with warehouse flooring. It was caused by overloading the surface area and was repairable without a pattern. You will want to use caution with heavy equipment such as personnel lifts even pallet jacks with enough weight "dropped" 2 inches can cause damage. The architect of the project should be able to give you an idea of what a safe working load would be.
  • Why does Concrete Crack?

    There are several reasons why concrete cracks, with the most common being drying shrinkage. Concrete, when placed in the plastic state, is at its largest volume. As the concrete sets and hardens, it begins to shrink. On average, concrete shrinks 1/8 inch in twenty feet.

    Concrete is typically designed for compressive strength and has significantly lower tensile strength. If the internal tensile stresses are greater than the tensile strength of the concrete, a crack can develop.

    Excess water in the concrete mix can also increase the probability of cracking. When placing the concrete, avoid adding extra water to the mix. The excess water will evaporate from the concrete which will lead to increased shrinkage. Make sure that you choose the proper concrete mix for your project.

    Sub-grade preparation is critical in providing a good base for your new concrete. The sub-grade should be smooth, uniform, have positive drainage and be free from frost. Without proper support, the concrete can settle and crack. A smooth sub-grade will reduce any restraint as the concrete shrinks thereby reducing the chances of cracking.

    Proper curing of the concrete is also crucial to help prevent early age cracking. Curing is the act of helping maintain concrete moisture by preventing its rapid loss. If the concrete loses moisture from its surface too quickly it will shrink (faster than the concrete below the surface) causing a condition referred to as map cracking. This condition is typically cosmetic and does not affect the structural integrity of the concrete. In some cases lack of curing can lead to more severe cracking that can require repair. Actively curing the concrete is always a recommended practice that improves the overall integrity of the concrete and further helps to prevent other surface defects such as scaling.
  • Polished concrete can crack same as any concrete. What I don't understand is why the architiect of this new project made the statement that it is likely to crack within the first year. Did he not provide the correct specs? Or did the installer not follow correct procedures?