In concrete surface preparation, there are several factors to consider when selecting the proper abrasive. Generally speaking, abrasives have two components: grit and bond. Both have important roles to play in the finishing of concrete!
We can’t use just any abrasive bond – if our team uses the wrong option, we’ll make our customers very unhappy with the finish! The correct abrasive bond for the material and the purpose can affect how well the job goes.
What Abrasive Bond Do We Use For Concrete?
Abrasives come in many shapes, sizes, and forms, made with bonding in a range of hardnesses. Grit is the abrasive particles measured in micrometres or microns; the bonding keeps the grit together on the paper. When looking at the options, note that the smaller the grit number on the package, the larger the grit particles.
The two primary bonding materials used are metal and resin:
- Metal abrasives blend micro-graded granulated metal oxides and powders. Harder metal bond abrasives use metals like brass, cobalt, and titanium, while softer bond metal abrasives often use copper.
- Resin abrasives use polyphenolic and ester-phenolic resins (for wet and dry use) or thermoplastic-phenolic resins (for dry use only). You can also find hybrids that combine bonding materials and ceramics.
Metal bond abrasives are used in coating removal and medium to heavy grinding. Use high grit metal bonded tools on softer concrete. Resin abrasives are ideal for honing, polishing, and light-to-medium grinding; they can also remove heavy metal bond scratch patterns.
How Do We Choose The Proper Abrasive Bond?
Choosing the proper abrasive bond starts by figuring out the concrete’s hardness. The concrete and its aggregate determine the hardness of the abrasive bonding for the most efficient cutting. It’s measured using the Mohs Hardness Scale; this rates materials on a scale of nine (hardest) to one (softest). When a concrete’s hardness is at the high and low extremes, we have to make special considerations. The general rule is that we use a harder bond on soft concrete, a softer bond on hard concrete, and a medium bond on medium hardness.
More than just the finish, the proper bond will affect the tool and work conditions. Hard concrete (seven through nine on the Mohs Scale) will break down an improper abrasive bond for the conditions. We have to use a softer abrasive bond that has low wear resistance so that, as we’re cutting, new grit becomes exposed. On the flip side, soft concrete needs a hard bonding because it produces an abrasive particulate that can wear down the bonding rapidly.
One way to understand bonds is to consider how much concrete is removed from a soft versus a hard concrete floor. When finishing a soft concrete floor, for example, you might take off more than five times the material than you would on a hard surface. For projects like this, we need an abrasive bond with a higher wear resistance!