Diamond Blades are Best for Cutting Concrete
If you thought diamonds were a girl’s best friend, you might be right, but they are also the best choice when cutting concrete.
When it comes to making clean, professional cuts in concrete, diamond saw blades are regarded as a perfect option. There are, though, a number of different options in terms of type and price.
It is important to understand how diamond blades work so you can choose a blade with the right cutting quality and characteristics for your needs.
First of all, diamond blades aren’t actually saw blades made with diamonds (as in gems). Rather, they are blades that are made using synthetic diamond crystals that cut absolutely anything – including concrete.
The rate of wear of the blade is controlled by the hardness of the matrix.
Diamond blades are used with power-driven tools, depending on the material to be cut. As the blade rotates at high speed, the abrasive action of the exposed crystals slices through the material. With continued use, the surface diamonds become worn and the matrix starts to shed, exposing sharp, new diamond crystals embedded within the matrix.
Choosing the Best Blade for Cutting Concrete
Diamond saw blades come in many different sizes and configurations to meet the varied requirements of users. These relate to the thickness of the blade and segment width. To ensure maximum blade life and cutting speed, it is important to match the blade as closely as possible to the material being cut. The blade you use for cutting reinforced concrete will not necessarily be the same as the type used for cutting asphalt, or even concrete slabs, even though most diamond blades cut through different type of materials.
As a general rule:
• A diamond blade for cutting relatively soft, abrasive, green uncured concrete needs a hard metal bond to ensure that exposed diamonds are utilized fully before shedding.
• Blades used to cut hard, nonabrasive concrete need to have a soft bond that allows for easier erosion of the matrix, ensuring exposure of sharp, new diamonds when needed.
According to blade manufacturers, a soft concrete material is one with a compressive strength of 3000 psi, and a hard concrete material is one with a compressive strength higher than 6000 psi. So a blade with a hard bond should be used for cutting lower-strength concrete, and a blade with a soft bond for high-psi concrete. Hard aggregate like quartz and basalt tend to dull diamond particles quite quickly, so you should use a blade with a softer bond.
Blade performance is also affected by the size of the coarse aggregate in the concrete. When cutting through larger aggregate (¾ inches or more), the blade will tend to cut and wear more slowly. Pea gravel (less than 3/8 inches) is easier to cut, but blades will wear more quickly.
The abrasiveness of concrete depends on the type of sand used in the mix, with round sand producing the least abrasiveness, and sharp, gritty sand the most. Sand sharpness is largely determined by its origin. Natural river sand is typically round and nonabrasive, while crusher sand from quarries is typically sharp. The more the abrasive the sand, the harder the bond requirements will be.
When and How to Cut Concrete
Assuming you plan to cut control joints in the concrete, you can cut it one or two hours after placing it, while it is still green. Alternatively, you can wait until it has begun to harden overnight. The type of blade chosen will depend on the timing of the cut.
Decorative concrete contractors often prefer cutting concrete when it is still green as it minimizes random cracking and allows for a shallower joint depth of one inch or less. However, green concrete is softer and more abrasive than concrete that has cured. This is because the mixture has not yet bonded to the mortar. Manufacturers of blades typically offer hard-bonded diamond blades specifically for cutting green concrete.
The other choice is between cutting concrete dry or wet. This will depend on your job requirements and preference. Dry cutting excludes the need to work with wet slurry and equip saws with hoses and water tanks, while using a wet blade reduces dust. A dry cutting blade and compatible saw may be the only option when working indoors where work areas must be kept dry.
The weld is the key difference between dry and wet blades. Dry-cutting blades have segment welds that are heat resistant and do not need water for cooling. They are typically intended for intermittent cutting and for use on low-horsepower, handheld saws. If you want to saw decorative patterns in concrete, dry-cutting blades will create clean, crisp cuts. Just remember that decorative cuts are usually 1/16 and ¼ inches deep and they don’t function as control joints.
Walk-behind saws use wet-cutting blades for making cuts in concrete that has cured, bearing in mind it takes 28 days to cure and reach its compressive strength. The benefit is that water-cooling allows for deeper cuts. While you can use many dry-cutting blades in wet conditions, you must never use wet-cutting blades without water. Cool the blade using water consistently to avoid blade warpage and segment loss.
Compatibility of Concrete Blades and Saw-Cutting Equipment
Manufacturers usually provide charts with recommended operating speeds for their blades. You will find this information stamped on the blade too.
Whether you are using a flat or handheld saw, always match the blade with the saw’s speed range. Operating the blade at a lower speed than recommended can reduce its performance and cutting life. Operating it at a higher speed can damage the blade and increase the risk of injury for the saw operator.
Most of the blades used for cutting green concrete are designed for use with special early-entry saws to minimize joint ravelling and even spalling. Avoid using blades that exceed the maximum blade diameter and the saw’s depth capacity.
Blade Cost Versus Performance
The cost and quality of diamond blades varies from basic economy level to professional, top-of-the-line premium types. The main difference is the diamond content, which is the greatest raw material cost in manufacturing these blades. It might cost you 20 per cent more to move up from a standard to premium blade, but the blade will have a higher diamond concentration and significantly longer life.
You need to decide what is most important to you: the total sawing cost or the initial cost of the blade. For small cutting jobs you can potentially save money if you choose the economy blade. For frequent use or large jobs, a top-quality blade could be cheaper in the long run based on a breakdown of cost per cut.
Premium grade diamond blades aren’t cheap.
You can expect to pay several hundred dollars or more depending on the diameter of the blade. If this is too much to spend for occasional cutting jobs, consider hiring a professional to do the work. The Concrete Sawing and Drilling Association (CSDA)’s directory will help you find a contractor in your location.