From the construction of the Hoover Dam to the back patio, concrete has become a way of life. While concrete finds a home in many architectural structures, such as foundations, bridges and overpasses, parking structures, and swimming pools, it is necessary for concrete construction contractors to perform concrete core strength testing to ensure the strength of the slab after it has cured. Concrete sawing and drilling companies hire testing labs that drill these cores, but the hefty fee leads many contractors to perform the task themselves. This requires a quality core drill, a testing machine, and the skill to do it safely. Cutting and drilling poses many dangers. Understanding how to safely use a concrete core drill helps keep workers safe.
Choosing a Concrete Core Drill
Though users can rent a core drill, most people taking the time to learn how to properly use it find it more economical to purchase a drill. Choosing the right drill and accessories for the job is important to safe operations. For those drilling holes up to 3 inches in diameter, a hand-held core drill works well. As the mid-size core needed for strength testing is 3.7 inches, using a rig-mounted drill or a concrete drill stand is the safest way of drilling. Hand-held units come in a variety of sizes for use with or without a drill stand. Purchasing a drill that is flexible enough to perform other tasks, such as drilling holes for plumbing or electrical work, or drilling dowel holes, increases the value of this investment.
Stand Attachment
A vacuum stand attaches to the floor with suction, eliminating the need for anchor holes. Its use, however, is limited to relatively smooth, flat surfaces. When drilling cores into uneven surfaces, or into walls, a stand with anchors is necessary. When anchoring, adjust the stand so it is level, and then secure it with physical anchors rated for core drilling. Additionally, a safety chain is highly recommended when using a stand.
The Right Diamond Bit
The diamond core bit must correspond to the material being drilled. This means you must consider the concrete psi and aggregate hardness when choosing the right bit. For hard materials, a softer diamond bond is best, and for softer materials, turn to a harder diamond bond.
Diamond Bond |
Material Density |
Examples |
| Hard | Softer | Marble, block, brick, and sandstone |
| Soft | Harder | Concrete, including reinforced concrete, granite, basalt, and flint |
Generally speaking, a hard diamond matrix, or bond, increases drilling time, while a softer bond prematurely wears away the diamond surface. If the diamond bit glazes over, drilling into an abrasive block reveals a renewed grinding surface.
Safety in Alternative Applications
While people most often use core drills in situations where the material gathered inside the drill bit, called the “core,” requires preservation, there are other applications in which a core drill operates safer and more quickly. When the situation calls for precise, circular cuts, core drilling provides a safe and effective solution. Holes up to 60 inches in diameter, in virtually any needed depth, created by a concrete core drill pull out the material with the bit, ensuring a clean-cut hole for such uses as floor and sewer drains; HVAC openings; phone, cable, and electrical openings; and even handrail anchors.
Inspecting the Drill
One of the most important steps to keeping workers safe is to inspect the core drilling machine daily. Check to make sure the drill is unplugged before performing this inspection.
* Check vacuum seal for wear
* Check power cord and plug for damage
* Inspect the machine for missing, broken, or misaligned parts
* Clean any oil, grease, or dirt from handles and controls
* Inspect the cutting edges of all drill bits for wear or damage
* Use this opportunity to lubricate the core drilling machine
Once you have ensured these items are in proper working order, you can proceed with the job.
Safety During Drill Operation
A core drilling machine is designed to drill holes in steel reinforced concrete, masonry, and granite. To reduce the risk of injury, never use the drill for other purposes, and be sure to follow the manufacturer’s instructions for use. When operating the drill, wear leather gloves, remove any loose clothing, and keep sleeves and jackets buttoned. Never reach across the machine or drill bit, and keep fingers and hands away from the drill bit, as this poses the risk of becoming entangled or being cut. Because heavy core samples drop from a hole drilled in a floor, use extreme caution to protect those beneath. Never force a drill bit, but use it at the speed and feed rate that does not overtax the motor.
