Back to Basics Part 1: Material Removal

A rule of thumb to keep in mind is: Hard concrete floors and coverings (such as epoxy), need a softer bonded metal tool. A harder bonded metal tool is used on soft concrete floors and abrasive coverings.

Every diamond manufacturer has recommendation charts to help contractors determine which diamond tools to use to remove various floor coverings. Once the correct diamond tools have been determined, there is a proper way to set up the diamonds to ensure they work efficiently.

Grinding disc set-up. Since grinding discs can hold a number of diamonds, it is essential to know the differences between using a half set or a full set.

A half set of diamonds means diamond tools are placed at three alternating positions on the diamond holder disc. When the diamonds are set-up as a half set, they tend to follow the surface of the floor. It is similar to a tripod for a camera, which can be placed on an uneven surface and still find stable footing. A half set puts more weight per square inch on the diamond tooling, making it grind more aggressively on hard floors. It does not completely flatten the floor.

With a full set, diamond tools are placed at each of six positions on the diamond holder disc. The full set of diamonds is used when a flat floor is desired. It grinds the high areas and misses the low spots, resulting in a smooth surface with no undulations.

See Table 1 for an explanation of when to use a half set or full set of grinding discs on certain applications.

In addition to metal bonded diamonds, a PCD (polycrystalline diamond) scraping tool might be necessary to remove heavy coatings. It is not recommended to use a PCD scraping tool directly on a concrete surface. If a PCD is required, an operator should start with the PCD tool, remove around 75 percent of the material and then use diamond tools to remove the remaining material.

Step 3 – Grinding process

Now that a grinder and diamonds have been chosen, it is time to start grinding. Concrete grinding is the simplest and most efficient method for leveling and restoring a concrete floor. While the grinder removes coatings, it creates the perfect base for a new floor covering.

Material can be removed by either using a dry grinding or wet grinding method. While both methods have the same end result, there are a few differences in the process:

Dry

• Production rates will be slower on harder materials than wet grinding
• Softer bond segments are required in order to encourage even segment wear
• Scratches from diamond grit will not be as deep when compared to wet grinding
• More heat is generated by the diamond segment
• Cleaner work environment

Wet

• Production rates will be higher than when dry grinding
• Diamond segments will wear faster due to the presence of abrasive slurry
• Scratches from diamond grit will be deeper
• Longer clean up time

Which method to choose is a personal preference. When either dry or wet grinding, start with a coarse grit diamond tool and progressively work down to fine grit tools — depending on the desired specification. Changing the size of the diamond grit to a smaller particle/grit size gradually removes scratches in the concrete and creates a fine scratch pattern. This creates a good bonding surface for a new floor covering.

After the grinding process has been completed, the final result is a good base for either a polished floor or another surface. Ending with the perfect base floor means the next step(s) will be finished more efficiently. Taking the time to think through the process and plan accordingly will make the project more efficient, easier and the customer will be happier in the long run.

Jamie Krueger, product manager for surface preparation, has been a part of the Husqvarna team for more than six years. He works extensively to understand the needs of surface preparation/polishing contractors and develop products that meet their needs.

Look for Part 2 of the Back to Basics series, “Industrial Flooring,” in the Spring 2013 issue of Polishing Contractor.