Concrete core drilling, or simply core drilling, is the name of an essential precision concrete cutting technique. Core drilling allows you to cut holes into any concrete, brick, or paved surface, including floors and walls. This cutting technique is essential for many applications, from preparing HVAC ducting to installing utilities like pipes and cables. Learn all about core drilling, which tools you need, and how to start drilling your first holes using this technique.
Basic Principles of Core Drilling
Core drilling requires a specialized tool called a core drill or coring tool. The purpose of a core drill is to cut large holes through masonry surfaces like brick, concrete, cement, sandstone, stucco, and tile. A core drill is the masonry equivalent of a hole saw for wood and plastic. The primary element of a core drill is the core drill bit (or annular cutter). A core drill bit is a hollow cylinder element tipped with teeth or an abrasive surface.
When its teeth are engaged into the desired surface, the rotating core drill bit progressively cuts a ring-shaped hole. As it advances and cuts through the surface, it leaves a cylindrical piece of uncut material called a core. The size and diameter of a core drill bit determine how far it can go until it is full of core materials. Once full, it can no longer advance. The core must be extracted and removed from the working surface, creating a cylindrical hole. Repeat and alternate the drilling and extracting processes until you have cut a hole of the desired length.
Types of Core Drill Bits
There is a wide selection of core drill bits available. However, selecting the right tool for your intended application is critical since using the wrong drill bit can damage or snap it. The two primary criteria of a core drill bit are its dimensions and type.
How to read core drill bit dimensions
A bit’s dimensions consist of two values: Diameter and length. The first number always refers to its diameter, indicating the diameter of the holes it cuts. For example, a 3” bit cuts 3” holes.
The second number indicates the core bit’s overall length. If the second number listed on the package is 17” then the bit is 17” long. Typically, the length of the cores produced by a drill bit is equal to the overall length minus the thickness at the base (typically ½”). For instance, a 17” bit may produce cores that are approximately 16½” long.
Bit dimensions typically match commonly utilized piping, cabling, or ducting. These standardized dimensions allow you to drill a hole of the perfect size to install the utilities of your choice. Occasionally, you may find core drill bits without a second number specified on the package. In these situations, the dimension listed is always the diameter.
Types of core drill bits
Most core drill bits are either carbide or diamond. Each type is suited for different applications.
Carbide core drill bits
Carbide core drill bits typically comprise a stainless steel body with tungsten carbide teeth, although some high-performance models are solid tungsten carbide. Carbide bits are the least expensive of the two options. They are generally durable and long-lasting, suitable for cutting holes into masonry materials from tile to concrete. However, carbide bits struggle against steel elements such as rebar. Grinding and repeated impacts on rebar tend to accelerate your carbide bit’s wear and may even chip or break it. Additionally, the holes produced by a carbide bit may not be as clean as a diamond bit. If you don’t need to cut clean holes and do not need to cut through rebar, steel, or other hard metals, a carbide core bit is a highly cost-effective solution.
Diamond core drill bits
At first glance, diamond core drill bits look similar to their carbide counterparts and may even feature bodies made of the same materials. The critical difference is in the tip: Diamond powder is embedded in each tooth, allowing a rotating diamond bit to grind through working surfaces with ease. Diamond bits are the more expensive option, but they offer numerous advantages. The diamonds’ unmatched hardness allows diamond bits to create cleaner, more visually appealing cuts. They also have no issues drilling through hard materials, such as steel or rebar.
Although they are highly durable and capable of cutting through more materials, the tradeoff is the heat they can generate. Continuous drilling through hard surfaces can rapidly heat up a diamond core bit. If allowed to heat up too much, they may warp or partially melt over the diamonds, significantly reducing their cutting effectiveness. At that point, your bit requires redressing or re-tipping to bring the diamonds back out. There are two subtypes of diamond bits:
- Dry cut bits: Dry cut models are used as-is, with no specific cooling system. They are primarily intended for indoor projects, using short bursts. If the bit gets too hot, it should be pulled out of the hole and allowed to cool down naturally in the air.
- Wet cut bits: Wet cut models are intended for use with a drill equipped with a water-cooling system. The water jet allows the bit to accumulate heat more slowly, letting you make longer cuts. Due to the water jets, wet cutting is best suited for outdoor projects.
What Tools Do I Need?
There are two categories of core drilling tools: Dedicated core drills and power drills. A dedicated core drill is intended explicitly for core drilling. These tools are typically more powerful, durable, and efficient than power drills. However, they are single-purpose tools that you cannot use for any other application. Power drills used for core drilling require you to slot a compatible arbor, then attach the drill bit to the arbor. If you intend to use this solution, ensure your power drill meets the following criteria:
- Rotary action drill, or hammer/SDS drill with a Rotary Only mode (you can use a hammer drill, but the hammer-action mode accelerates bit wear and tear)
- Voltage rating of at least 24 V (if cordless)
- Power ranging between 800 and 1300 W
- Variable speed function
- Safety clutch
Regardless of the type of drill or core bit you use, you will need a second drill bit called a guide bit. Guide bits resemble traditional drill bits, but their primary purpose is to help you center your core bit during the first few inches, avoiding any misalignment.
How to Use a Core Drill
If you want to learn how to drill through tile, concrete, brick, or any other common household wall or floor, here are the steps you should follow.
Before you start any drilling work, ensure there are no existing cables, pipes, utilities, or other sensitive equipment behind the surface you intend to drill through (especially walls.) Specialized equipment, such as wire detectors or stud finders, can help you locate potential obstacles before you start drilling, allowing you to relocate or work around them.
If possible, measure the wall’s thickness because this lets you know exactly how deep your drill core bit must travel to reach the other side. With a core bit of the right length, you can drill through your wall in a single pass instead of multiples, saving you a significant amount of time.
Once you have your wall dimensions, use a pencil to mark the spot you intend to drill through.
Configuring the drill
Select a core drill bit of appropriate type and length for your working surface. If possible, use a bit that is slightly longer than your wall’s thickness. You can then prepare your drill. The process may vary depending on the type of drill you possess. If you have a power drill, attach the core bit to the arbor first, slot the arbor-bit assembly in second, then install the guide drill bit last. If applicable, disable the hammer-action mode. Lastly, set your drill to a speed setting appropriate for your hole’s diameter. Follow this size-to-RPM chart to find the best speed setting:
- 2”: 1300-1900 RPM
- 2½”: 1000-1500 RPM
- 3”: 875-1325 RPM
- 3½”: 725-1075 RPM
- 4”: 650-950 RPM
- 4½”: 550-850 RPM
- 5”: 525-800 RPM
- 5½”: 475-700 RPM
- 6”: 425-625 RPM
- 6½”: 400-600 RPM
- 7”: 375-550 RPM
- 8”: 325-475 RPM
- 9”: 275-425 RPM
- 10”: 250-350 RPM
Align your drill in front of your working surface by placing the guide bit onto the pencil marking. Make sure the guide bit is as perpendicular to the surface as possible (horizontal when drilling a wall, vertical on floors.) Misalignments cause you to drill a hole at an angle, creating an unwanted slope. Start drilling with the guide bit at low RPM until the core bit’s teeth start engaging your working surface. When your core bit’s teeth contact the wall or floor, you may feel them “bite” into the surface. Keep drilling until your core bit cuts approximately 1” into the surface, then pull the drill back.
At this point, you should have a ring-shaped cut into your wall or floor. Remove the guide bit, reinsert your core bit into the ring-shaped cut, and resume drilling, progressing forward as carefully as possible. Keep your drill level and perpendicular at all times.Stop and pull the core bit back regularly (every 5-10 seconds) to let your bit cool down. Ensure the bit is still rotating while pulling out to avoid jamming. While your core bit dissipates some heat, inspect your cuts and look for symptoms of misalignment. If your drill is not level, you should see one side cut slightly deeper than the other. There are two possibilities from there, depending on whether your core drill bit is longer than the wall or floor’s thickness.
- Core bit length longer than surface thickness: You will successfully drill the hole in a single pass. At that point, the core should slide out of your core bit and fall on the other side.
- Core bit length shorter than surface thickness: You will be unable to complete the drilling in a single pass, requiring additional steps.
Completing a hole in multiple passes
If your core drill bit isn’t long enough to finish the hole in one go, you will need to pull your drill back and extract the core out of your hole manually. Do not, under any circumstances, try to force the core out by pushing it, even if you are less than an inch away from the other side; you risk cracking the wall and causing severe damage. Instead, follow these steps:
- Insert a chisel between the core and the wall or floor.
- Use a hammer to tap the back of the chisel until the core snaps.
- Extract the core from the wall with a large pair of pliers or a pair of screwdrivers.
You do not need to remove the entirety of the core; only enough to give your core bit the clearance it needs to continue drilling and reach the other side. If your core drill bit is less than 2” from the other side of your working surface, reattach your guide bit and drill until the guide bit pokes out of the other side, creating a second guiding hole. Ask a partner to spot and warn you when the guide bit becomes visible on the other side. Once it does, stop drilling and move your equipment to the other side.
The purpose of this new guiding hole is to help you center your core bit on the other side, allowing you to finish with a clean and perfectly aligned exit hole. Place your core bit around the guiding hole, using the guiding bit to center it just as you did when you started. Push until the core bit’s teeth engage the wall or floor, then drill the remaining inches out. Clean the core bits out of the hole and inspect the interior. If you’ve followed every step correctly, you should have a perfectly cut, straight hole through the wall or floor of your choosing.
Shop Top-Quality Core Drilling Tools at Contractors Direct
With patience, some practice, and the right tools, you can core drill virtually any wall or floor in your home. The primary challenge is maintaining a good grip and a steady hand to avoid drilling at unwanted angles. At Contractors Direct, we aim to provide you with the highest-quality tools, at the lowest prices, and with the best customer service. For any information on core drilling or other projects, contact us today.