When preparing your concrete surface, it is important to understand which set of diamonds will give you the proper results. Even with the right equipment, the wrong set of diamonds can cause problems ranging from scratches to glazing. This happens because the density and hardness of concrete can vary greatly, and is directly affected by what materials were used to create it. Different materials are used in different regions due to what is most readily available. The best way to know which diamonds to use is to perform a MOHS hardness test on your concrete before grinding.

First, you need to learn how to perform the test properly. The MOHS hardness test kit that we have available for your use comes with tester pieces, which are small thin rectangular pieces of different materials that scratch on different levels. There is a label on each piece identifying which hardness level that material is. The objective is to use these pieces to first train your hand to use the correct amount of pressure with these guides. Only then, will you understand how to properly test your floor. Hold the tool like a pencil and press the point into the tester piece. Then pull it forward to draw a line. When it makes a scratch, remember the amount of pressure used. Do NOT try and force the tool to scratch the surface. Repeat this process until the amount of pressure feels natural.

After you have learned the proper pressure to apply:

  1. Hold the #9 tool like a pencil and press its point on the concrete surface.
  2. Pull a 2” line toward you and note mentally how much it scratched. (When the tool leaves an etched line on the surface of your concrete, it indicates that the floor is softer than the numbered tool just used.)
  3. Continue to progress down in numbers until the numbered tool you’re using doesn’t scratch.
  4. The concrete’s hardness will be the previous number of the tool that didn’t scratch the concrete surface.
  5. If there is a questionable result, test another fresh/clean area of the concrete surface to establish the hardness of the floor on average.
  6. After you know your concrete’s hardness, use the corresponding color of metal-bond diamond sets with your grinder to open the floor.

Mohs Test Hardness Results – Which Diamond to Use

Hardness of 3 – 6  = Medium ConcreteUse Medium Bond Diamonds
Hardness of 7 – 9 = Hard ConcreteUse Extra Soft Bond Diamonds

Overall, you should remember this simple rule: Use harder bond diamonds for softer concrete and softer bond diamonds for harder concrete.

More detailed instructions are included in the test kit and should be strictly followed. You can also find a helpful video available from WerkMaster at https://www.werkmaster.com/mohs-concrete-tester.

It is also important to note that you can repeat the hardness test before each step of grinding if needed. This can be useful because many times the cap of the concrete is harder than the slab’s matrix. So, if you continue using the set of diamonds that were required to get through that hard cap, the new hardness level can abrade the softer-bond diamonds, resulting in excessive wear of the tooling.

Pay close attention during your grinding process to troubleshoot problems early. Are your medium-bond diamonds glazing and heating up? Switch to extra soft bond diamonds! If you are having glazing issues, we also recommend reducing your grinding speed and RPM. Grind Slower!  Lastly, you may want to consider using some water on the floor if you continue to have glazing problems.