In order for contractors to be efficient and profitable in the concrete grinding and polishing industry, they need to understand that the end use cost of an abrasive is different from the purchase cost of the abrasive. End use cost is the cost of the abrasive set divided by the square feet the abrasive produces before it is no longer useable and the cost of labor required to effectively use that abrasive.
If an abrasive cost seems too good to be true, it probably is. Don’t base your purchasing decision on price. For an abrasive to be effective it has to fully refine the concrete from one grit to the next. Let’s take a look at the basics of bonded abrasives and the factors that affect abrasive cost and labor cost.
Grit is measured in micrometers (also called microns) and assigned a numeric value based on its size. The smaller the grit designation, the larger the grit particle is. Exact sizing of particulate is expensive so an abrasive will have a range of particulate with overlapping sizes. For example, an abrasive classified as 120-grit will not only contain 120-grit but also have a percentage of 100-grit and 150-grit. A typical grit sequence for polishing concrete does not contain all of the grit sizes available to an abrasive manufacturer. Instead, beginning with the starting grit, each consecutive grit approximately doubles in size.
Man-made material is most often used due to expense and the ability to create consistency. Man-made particulate comes in various forms of alumina, silicon carbide and most widely used are superabrasives made from cubic boron nitride and synthetic diamond. The individual grains of grit come in different shapes and strengths. Quality manufacturers will have products with properly dispersed grit in the abrasive bond, proper grading of the grit particulate and quality particulate that won’t easily fracture or crush.
Grit particulate is bonded together by various bonding material to form an abrasive. Abrasives may be made through an injection process, hot and cold pressing, electroplated, or vacuum brazed. The two primary bonding materials used are metal and resin. Metal abrasives are made from a blend of micro-graded, granulated metal oxides and/or powders. Harder metal-bond abrasives are made from cobalt, brass and titanium. Softer bonded metal abrasives may be made from copper. Resin abrasives are made from poly-phenolic and esterphenolic for wet and dry use and thermoplastic-phenolic resins for dry use only. Also on the market are hybrids that are made from a combination of bonding materials and ceramics.
Shapes and sizes
Bonded abrasives have contact area and non-contact area. The area that is in contact with the concrete surface is an additional factor that determines how much abrading the abrasive is capable of producing.
End use cost variables
The quicker an abrasive can produce a fully refined surface throughout a determined sequence, the quicker a crew can get on and off the job. An abrasive’s bonding is the most important consideration that affects the actual end use cost.
For an abrasive to most efficiently work, the bonding must wear at the same rate at which the concrete is being abraded. For this to happen the bonding must be matched to the hardness of the concrete and work in conjunction with the weight of the machine, the speed the abrasive is driven, the rotational direction the abrasives are driven, and the rate an operator moves the machine in a liner motion. Most machines allow an operator to add or remove weight and adjust the rotational and liner speed allowing an operator to take maximum advantage of the type and hardness of the bonding.