Bond & Grit
The segments on a surface prep tool consist of a mixture of diamonds and metal powders, the so-called bond. The bond plays a key role in a tool’s performance as it determines the strength of the material that can be ground. With time the diamonds fracture or are pulled out of the bond. Simultaneously the bond wears away exposing new diamonds. Here it is important to select the right bond for the material being ground.
As a rule of thumb, the harder the material, the softer the bond should be and vice versa – opposites attract! When grinding very abrasive material such as rain-damaged concrete or asphalt the bond needs to be hard otherwise it will wear away too fast, causing the diamonds to fall out too soon. A strong bond however will support the diamonds and increase the life of the tool. When grinding hard material, for example, cured, high psi or hard-trowelled concrete, the bond needs to be soft or else it will not wear away fast enough resulting in the segments glazing over.
The grit is the particle size of the diamond held in the bond and determines the finish. The lower the number, the larger the piece of diamond (coarser grit). The higher the number, the smaller the piece of diamond (finer grit). Often several steps with different grits are required to achieve the desired results. Generally speaking, the higher the grit, the finer the finish. First, a low grit is used for aggressive removal of coatings, then higher grits are used to remove scratches from lower grits, polish the concrete and lastly achieve a shiny surface.
If the concrete is in really good shape and you are after more of a salt and pepper finish, it is best not to start with 30/40 grit and move straight to 60/80 grit. This way you will not expose as much aggregate, but you will end up with a smoother floor after just one step, rather than having to remove 30/40 grit scratches if there is no need to.