Selecting the wrong diamond blade for a concrete saw is a common and costly mistake. A mismatched blade can lead to a longer and less productive job, a decrease in profit, and sometimes, serious damage to expensive equipment. With so many blades available for so many different job applications, finding the right one can seem like searching for a diamond in the rough. Fortunately, this common error is avoidable with practical selection guidelines to ensure proper diamond blade selection.

First, analyze the composition of the concrete to be cut. Concrete aggregate hardness varies across the country and even across states. Standard evaluations, including density tests and core samples, can help determine the nature of the aggregate. Will you be cutting hard, cured concrete, or softer materials such as asphalt and green concrete? Concrete density should always be considered when selecting the appropriate blade. The material to be cut determines what kind of metal bonding agents will be used in the matrix, which holds the diamond chips in the segments on the cutting blade. The matrix is a formulated mixture of various metals that determines the rate at which the diamond chips in the segment are sloughed off.

The matrix, including the diamond chips, is measured into the segment form and "cooked" at a high temperature until the bond is complete. The formed segments are then brazed or laser welded to the core of the steel blade.

When cutting hard materials, choose a softer matrix. The softer bond will release the diamond chips at the point of maximum utilization without the danger of holding the diamond long enough to be overexposed to heat at the cutting point. If the overexposed diamond is not sloughed off in time, it will glaze over and stop cutting. The glazed-over surface will stop the entire sloughing off process and the blade will stop cutting because there are no new diamond chips being exposed at the cutting edge. The diamond blade will be useless even though the segment has not been completely utilized.

When cutting soft materials, select a harder matrix that will hold the diamond chips longer so they can be more productive. If you use a soft bond with soft concrete, the bonding matrix will release the diamond chips before they have reached maximum utilization and good diamond cutting chips will be lost prematurely. The blade will still cut adequately, but productivity will suffer.

The type of blade chosen to do a particular job depends largely on the type of saw being used and the specific cutting application. Electric and pneumatic saws generate enough power to run smaller diameter blades (up to 20 inches), while gas- and hydraulic-powered saws are capable of driving larger blades (24 to 26 inches).

In replacing a sewer line, which requires miles of deep street cuts at a depth of eight inches, maximum production would be obtained using a 35 to 65 hp gas-powered saw with a 28-in. blade that provides the optimum power, productivity and mobility for the application. On the other hand, if a crew were cutting out new water meter boxes in a neighborhood that required more shallow cuts of three and one-half inches, a smaller, more easily manipulated saw with a smaller diamond blade - perhaps a walk-behind road saw - would be most effective.

The diameter and width of blade used are dependent upon the application. The depth and width of cut required on the job will determine the blade; blade requirement will determine the type of saw needed to power the blade. Blade selection and number of diamond segments per blade are likewise dependent upon applications.

For high productivity in cutting one and one-half inches deep, a blade with more segments (more diamond surface exposure) is needed. Cutting five inches deep in hard concrete, fewer diamond segments (more gullets and space between segments) are preferred to keep the blade cool and prevent overheating.

Larger saws with the ability to drive 20-in. blades or larger generate increased friction and heat in the cut. These saws typically use wet-cut blades that require water to keep the blade cool. Smaller diameter blades driven by saws turning at speeds of 3,500 to 5,400 rpm are kept cool by the increased airflow generated at high speeds, so dry-cut blades are used.

Realistically, the most important individual consideration when selecting a diamond blade is cost versus production. As previously described, diamond blade segments are a mixture of metals and industrial diamond chips. Diamond concentration, which varies among blades, is the primary determinant of price. Premium blades contain the highest amounts of diamond concentration and usually carry the larger price tag.

A premium blade will cost more initially, but will outlive and outperform most standard blades. It is important to remember that damage to a blade is not easily repaired and many times requires replacement. A premium blade with the proper bonding matrix will always outperform a lower priced blade with fewer diamonds. The goal of any contractor cutting concrete is to minimize the cost per in./ft. of cutting.

The standard for measuring blade life is the number of linear feet multiplied by the depth of cut divided into the price of the blade. For example, if a $495 blade cuts 1,700 linear feet at an average depth of three inches, the formula would read as follows:

$495.00 = $495.00 = $0.097 per in./ft. 1,700 ft. x 3 in. 5,100 in./ft.

Diamond blades vary in width from one-eighth to one-half inch, and carry various numbers of segments depending on the design. Choices between bonding requirements, diamond concentration and wet or dry applications also help to complicate matters. With so many options, it pays to know which diamond blade is the right one.

Sawtec portable walk-behind and hand-held air powered saws are environmentally friendly and safe-cutting options. Suitable for cutting depths of up to eight inches, they are designed to cut dry, but also feature standard water feed systems and optional water tank kits for the walk-behind models. The Sawtec handheld series includes the HS-50, HS-100, HS-125 and HS-150 models. These lightweight machines suit demolition, bridge repair, sidewalk repair, pile cutting or pipe cutting. Sawtec offers the FS-60 and the FS-150 air-powered walk-behind saws for use when cutting concrete and asphalt. The HS and FS saws feature either a 5 hp direct drive motor or a 7.5 hp air motor with gearbox.

Sawtec, a division of USF Surface Preparation Group, offers a full line of portable dust-free surface preparation equipment including air-powered saws; grinding equipment; tile cutting, tuck-pointing and crack chasing equipment; joint cleanout equipment and dust collection systems. The line also includes a full complement of standard and premium diamond blades, cup wheels and abrasive discs.