Select the Right Cutting Blade to Improve Efficiency.
Selecting the right blade for a concrete cutting application can improve efficiency and reduce costs. Blades vary by the number of diamond crystals, size, shape, cost and performance, but the quality of the blade and its diamonds is the true differentiator.
Contractors often want to know which blade works best in concrete and how large the blade should be. The answers to these questions fall into four categories: 1. hardness of the material to be cut, 2. speed and size of the blade needed, 3. cut desired and 4. efficiency, longevity and affordability.
High-quality diamonds will allow a blade to perform better over a longer period of time.
Types of Blades
Concrete cutting blades come in three major groups.
Segmented blades are the most common option used for fast cutting in concrete. With segments of varying sizes around the perimeter, the gullets (gaps) between the segments accumulate dust and expel it, allowing the user to efficiently cut the concrete. The gullets also keep the blade cool. These blades are best for high production jobs.
Continuous rim blades provide fast and clean cutting with minimum chipping at a reasonable cost and can be used in small or large diameters. They cut more slowly and are used when precision is needed (for tile cutting or cutting for length on concrete countertops).
Turbo blades combine the advantages of continuous rim and segmented blades and can be used wet or dry. This type of blade can simulate the precision of continuous rim blades but allows the dust generated to accumulate in the gaps. They provide a good-quality cut at high speed and are used in many applications, including repair work.
Criteria for Selecting the Right Blade
Longevity and Cost
Manufacturers offer diamond blades at different quality and cost levels ranging from basic economy to premium, which can cost hundreds of dollars. The difference is in the diamond content.
Upgrading from standard to premium may raise the cost 20 percent or more, but the blade will have a significantly longer blade life. For small cutting jobs, a savvy user may opt for an economy blade. But for frequent cutting, a concrete professional will save money on a cost-per-cut basis with a premium blade. In the process of cutting, it is about maximizing the cost-of-cut per inch or per foot. The blade's ROI can be calculated by dividing the blade's cost by the length times width of the cuts made.
Cutting hard concrete shortens blade life and reduces cutting speed. For a heavy job with an economy blade, it may be necessary to change the blade daily. A premium blade may last a week on the same job. The fewer blade changes, the faster the job will go and the more money a smart concrete contractor can make.
Concrete's content can be crushed aggregate (limestone, granite or sandstone) or uncrushed, fine or coarse. The amount of sand in the aggregate also affects the concrete's hardness and abrasiveness. A lot of sand in a concrete mix will age a blade faster.
Aggregates are geographically similar with some variation. For example, Florida is notorious for softer concrete, and St. Louis, Mo. is famous for its flint-based aggregate, which is extremely hard. Find an aggregate map of the United States to use as a general guide, then select your blade accordingly. Large or hard aggregates cause blades to cut more slowly and are harder to cut, requiring a softer bond. Small or soft aggregates are easy and fast to cut and require a harder metal bond.
As a general rule, the deeper the cut needed, the bigger the blade required. Not all grinders can take all blades sizes, so consider the tool as well.
Green concrete (0-8 hours old) requires a harder-bonded diamond blade than cured concrete (anything over 8 hours), which requires a softer bond.
Concrete hardness is measured in pounds per square inch (PSI). Roads, sidewalks, patios, parking lots and indoor concrete tend to range from soft to medium. Bridges, piers and nuclear plants are hard or very hard applications. The higher the compressive strength and the harder the material, the softer the bond required.
Rebar or wire mesh in the concrete will cause slower cutting rates, reducing the blade life by as much as 75 percent if the concrete has 3 percent steel.
Size and Speed
The three blades styles are produced in several sizes, with larger sizes developed for walk-behind units. Consider the grinder's horsepower and operation speed and the type of job. Blade manufacturers provide charts with recommended operation speeds and maximum safety speeds for their blades, which is stamped on the blade.
Wet or Dry
Make sure a blade can be used for the application needed. Wet cutting is used for outdoor jobs when making a slurry will not be harmful. Dry cutting is almost exclusively done on indoor jobs but is also done outside. Blades are designed for wet use, dry use or both. Never use a wet-use blade without cooling it (with water), or its life will be considerably shortened.
As a rule of thumb, rely on the product packaging when buying a blade for a specific application. The best diamond blade manufacturers help identify the right blade for the job with easy-to-read size and color application photos on the packages.
Knowing the concrete's composition and the grinder or cutting system will dictate the best possible blade choice. Quality diamonds make the biggest difference.