How-To: Core Drilling, Rock Drilling, and Grouting

Objective: By completing this lesson, you will acquire the skills to perform core drilling and rock drilling into existing surfaces, followed by the correct technique for mixing and pouring grout.

Key Questions:

  1. What essential knowledge is required when working with Quik-Rock or other fast-setting grout?
  2. What are the appropriate dimensions for drilling in terms of depth and width?
  3. How do you effectively pour grout around a post?
  4. Elaborate on the concept that core drilling or rock drilling operates as a two-way process.
  5. How to execute rock drilling accurately.
  6. How to carry out core drilling with precision.

What considerations are vital when handling Quik-Rock or other fast-setting grout?

  1. Perfect temperature is 70 degrees.
  2. Add cold water if warmer and hot water if colder.
  3. Never use quick-rock in temperatures below 30 degrees.
  4. If using more than five pounds of grout, mix vigorously with mechanical means such as powered blender.
  5. Pour grout within five minutes of initial mix.
  6. Always cap or crown hole to assure water run-off. If salt exposure is possible, grouted area should be sealed with concrete sealer. Quik-Rock is very susceptible to salt and will cause the material to break down.

See the guide before for Quik-Rock mixing. For posts larger than 3”, the hole must be at least 1 ½” – 2” larger than post. No exceptions.

If using Quik- Rok as an additive to concrete, use the 1:2:3 mix below:

Quik Rock : Portland :  Gravel.

Minimize water usage to the necessary extent for achieving flow, avoiding excessive water which can degrade the grout's quality.

When incorporating Quik-Rock as an additive to concrete, ensure that the hole's diameter is three times that of the posts. For instance, a 3-inch post would necessitate a 9-inch diameter hole.

To enhance your effectiveness when working with Quik-Rock, implement these supplementary measures:

  1. Cut slits into the post to add key ways. These slits significantly increases the gripping strength of the grout to the post. This has been the biggest challenge with use is that post will later break free from grout.
  2. Widen your gap between post to allow materials to flow all around post.

What is the necessary depth and width for drilling?

The tendency to drill or core excessively deep stems from an absence of clear specifications or understanding. This leads to attempts to drill or core to an excessive extent, as if aiming for the center of the Earth. However, it's important to recognize that surpassing the required drilling or coring dimensions doesn't yield extra advantages; instead, it only adds unnecessary expenses. For the purpose of this educational context, we will consider that referencing core drilling also encompasses relevant aspects of rock drilling.

Drilling need not persist until reaching the earth's core or its very bottom. It is acceptable to avoid drilling all the way through the slab. The planet's rotation won't cease due to this. According to ASTM F 567...

For a 2 ½” diameter post, drill to a depth of  7 ½”.

This actually exceeds the requirement outlined in the Federal Specification RRF-191, which stipulates a depth of 6". It's important to note that we're anchoring into the slab, thus the post's integrity is contingent upon the slab's performance. No supplementary foundation is needed.

Following the guidelines of ASTM 567 and adhering to established norms, there's no need to persistently drill. The additional few inches usually aimed for at the bottom aren't consistently necessary and incur both time and material costs.

When it comes to pouring grout around a post, maintain a minimum ½” gap surrounding the post. This allows the grout to flow uninhibited and fill the space. For a post with a diameter of 2 ½”, employ a rock drill bit or core drill measuring at least 3 ½”.

Here's a useful tip:

  1. When preparing grout, trim the top of the plastic bottle or whichever container you're using for mixing at a 45-degree angle. This alteration facilitates pouring the grout into the void even when tilting the container.
  2. Position your post within the cored hole, ensuring it aligns with the correct height.
  3. Employ three small wooden shims to level the post within the hole.
  4. Follow the manufacturer's specifications to mix the grout appropriately. The initial mixture should exhibit a consistency similar to that of a well-made milkshake.
  5. Pour the mixture around the post, ensuring it comprehensively fills all gaps. Maintain the pour level around 5/8” below the top of the finished grade.
  6. Allow the grout to set, subsequently removing the shims.
  7. Prepare another batch of grout, adjusting the consistency to be between that of a milkshake and regular milk.
  8. Pour this final mixture around the post, creating a slightly elevated surface above the finished grade to ensure effective water runoff. The less viscous consistency will result in a smooth, uniform surface on top.
  9. For projects involving decorative, colored, or stone surfaces, cut the bottom off a plastic bag. Insert the bag into the hole, positioning it so that the bag's sides extend about ½” into the hole, with the remaining portion folded over the top and resting flat on the surface. Pour the grout following the previously mentioned steps. Once complete, utilize a razor knife to trim around the bag's edge where it meets the surface. The folded portion of the bag will capture any overflow or drips, simplifying disposal.

Core drilling and rock drilling have limitations and aren't boundless in scope.

Determining their extent involves not only considering the diameter but also the depth. When assessing a project involving drilling, it's essential to account for the material's depth that will undergo coring or drilling. If there's uncertainty, consult the owner or contractor. The illustration below depicts the typical paving thickness according to its intended application, serving as a reliable guideline. However, this guideline does not extend to asphalt. While most asphalt slabs measure less than six inches in thickness, this measurement can significantly differ due to subsequent layers being added over time. It's not uncommon to encounter asphalt slabs exceeding one foot in thickness.

Addressing core drilling or rock drilling involves a dual perspective. It necessitates precise specifications not only for our customers, outlining the core depth, but also for our installation teams. Regrettably, our installers have developed a habit of drilling until they hit oil or dirt. Our sales and supervisory staff must convey to them that...

“We figured 7 ½” deep.  If you have not reached dirt by then, stop.  Any deeper and we will have to get a change order.”

Now, what exactly is rock drilling? Rock drilling refers to a tool that combines hammering and rotational movement, akin to a jackhammer. It's primarily employed on concrete and similar surfaces. Its design is geared towards breaking down and subsequently removing the affected area, rather than cutting.

A rock drill comprises three main components: the body, shaft, and bit. The body connects to a high CFM compressor. Upon engaging the trigger and introducing air, the shaft and attached bit commence both spinning and hammering. Air travels down the shaft's center and through the bit to expel dust.

To effectively operate a rock drill, follow these steps:

  1. Ensure Proper Personal Protective Equipment (PPE): Prior to starting, put on appropriate PPE, including safety glasses, ear protection, and steel-toed boots.

  2. Mark Hole Locations: Clearly mark the locations where you intend to drill holes on the surface.

  3. Mark Drill Bit Depth: Using markings on the drill bit shaft, indicate the desired drilling depth.

  4. Connect Drill to Compressor: Attach the rock drill to a high-CFM compressor. Ensure all hoses are correctly connected, using safety whips at each connection point for added security.

  5. Check Hoses and Inline Oiler: Pass hoses through an inline oiler and ensure it's filled with oil. Test oil flow by placing a white sheet of paper at the hose end under pressure, verifying a consistent light oil pattern.

  6. Attach Drill Bit Tip: Screw the tip onto the drill bit shaft, following the reversed threads.

  7. Mark Shaft Depth: Indicate the intended drilling depth on the drill bit shaft.

  8. Prepare Drill for Insertion: Release the lever at the shaft insertion point. Insert the tipped shaft into the rock drill and engage the lever to secure the shaft.

  9. Set Drill to Off Position: Ensure the drill is set to the off position before starting the compressor.

  10. Inspect Hose Connections: Thoroughly check all hose connections for kinks, loose fittings, leaks, and proper safety whip placement.

  11. Position the Drill: Stand the drill upright and align the bit with the marked hole location. Center the drill between your legs and shoulders. Gradually engage the drill while applying gentle pressure to prevent excessive bouncing.

  12. Stabilize with Feet: To stabilize the bit, you can use your feet, provided you're wearing steel-toed work boots. Operate the drill at a slow speed to avoid excessive bouncing that could potentially harm your feet.

  13. Start Drilling: Once the drill has established a centered position and created an initial hole outline, you can increase the drill speed and reduce the downward pressure.

  14. Optimal Drilling Technique: Decreasing downward pressure allows the bit to move up and down and rotate, effectively pulverizing the surface and clearing debris through the central shaft. This technique also aids in removing debris with the airflow.

  15. Drill to Desired Depth: Drill only to the desired depth and then disengage the drill. Carefully remove the drill bit from the hole.

  16. Inspect Hole Depth and Consistency: Check the drilled holes for the intended depth and consistent quality.

  17. Clean Holes: Thoroughly remove any remaining dust and debris from the holes. This step is crucial; grout adheres best to clean hole surfaces, ensuring a secure bond.


What is Core Drilling?

Core drilling refers to the technique of removing a cylindrical section of material using a hollow, cylindrical drill. This method finds applications across various industries such as construction, mining, geotechnical engineering, and research. Core drilling serves not only to create holes but also to extract material for closer examination. The core drill consists of three key components: a motor, a handle, and the cutting bit.

How Does Core Drilling Operate?

Concrete core drilling demands the use of a diamond-tipped drill bit specially designed for this purpose. These drill bits are essentially steel tubes embedded with industrial diamond fragments. The drill bit is affixed to the shaft of the drilling machine, which is then secured to the surface being drilled. After the core drilling process is completed, a solid cylindrical piece of material, known as a "slug" or core, remains within the hollow drill bit. The drill's hollow center ensures that the extracted core remains contained until it is removed.

It's worth noting that core drills are versatile and capable of cutting through a range of materials beyond concrete. These materials include porcelain tile, limestone, rock, granite, fiberglass, and even ice.

Job Site Preparation:

  1. Get the core drill and the job site ready.
  2. Prior to commencing core drill operations, it's crucial to prepare the job site and ensure the drill is in optimal condition. Follow these steps:
  3. Inspect the alignment and movement of parts, mounting, and other factors that might impact the core drill's operation. Refrain from using the core drill if any signs of damage are evident.
  4. Thoroughly read and comprehend the operational manual.
  5. Verify that the power supply's flow and pressure meet the core drill's requirements.
  6. Examine the vicinity for active electrical wiring near the work area or embedded within the material that will be drilled.
  7. When drilling through a wall, assess both sides for potential obstacles.
  8. Before drilling through a floor, safeguard all individuals and materials beneath the work zone. Typically, drill cores drop from the bit after the hole is complete.
  9. Ensure that all personnel are wearing appropriate safety gear.
  10. Clear the work area of all unauthorized personnel. Implement barricades or secure the area to prevent any potential injuries.

Anchoring the Core Drill:

  1. The core drill can be anchored using bolt anchoring or ceiling jack anchoring on the floor, or bolt anchoring on the wall.
  2. Measure the distance from the center of the anchor bolt slot in the base to the center of the drill spindle.
  3. Mark from the center of the hole on the floor, which is going to be drilled, to the intended location of the anchor bolt hole.
  4. Proceed to drill and install the anchor bolt. Then, position the core drill over the anchor hole and gently tighten the bolt by hand.
  5. Ensure the stability of the core drill by securely tightening the anchor bolt.
  6. Before anchoring, confirm with your customer whether anchor holes can be drilled next to each cored hole. These anchor holes will remain and should be filled with grout. Inform the customer that these holes will be visible once the project is complete. Note that leaving anchor bolt holes in decorative stone, brick, concrete, or similar materials with decorative and colored finishes is generally considered unacceptable.
  7. Inadequate anchoring of a core drill rig can lead to severe bodily harm. Drill rig motors operate at high speeds and torque, emphasizing the importance of proper anchoring.

Installing a Drill Bit:

  1. Prior to installing the drill bit, ensure that both the bit and the core drill are at a safe temperature. Additionally, always remember to wear protective gloves when handling, installing, and removing core drill bits.
  2. Verify that the cutting teeth of the bit are visibly in good condition and show signs of useful life.
  3. Confirm that the bit maintains an appropriate shape and is neither perfectly round nor oval.
  4. Inspect the bit for any dents or deformations caused by hammering to extract the core in previous uses.
  5. Any damage to the bit's structure will result in binding within the hole, leading the core drill rig to exert more effort than the standard operating torque. This can eventually lead to the wearing out of the winding and motor over time.
  6. Proceed to remove any dirt or contaminants that might have accumulated on either the bit or the drill spindle.
  7. Mark the side of the bit to indicate the desired cutting depth.
  8. With the depth marked, carefully thread the drill bit onto the drill spindle and securely tighten it using a bit wrench.

Comparison of Wet Drilling and Dry Drilling:

Depending on the specific application, workers may need to opt for either wet or dry core drilling methods.

Wet Core Drilling: Wet core drilling stands out as the more efficient of the two techniques. When using wet drills, the bit typically advances through the core faster than dry bits due to the lubrication provided by water, which loosens the material's surface. Additionally, wet core drilling results in a cleaner and more stable hole surface since the water minimizes the dust generated during the drilling process. This method is best suited for materials like concrete, soft or hard brick, and reinforced concrete. Core drill bits operated with wet lubrication tend to have a longer lifespan compared to dry-running bits, as the water serves as a coolant, dissipating the heat generated during operation. The work speed itself also influences the durability of the bit. However, a challenge with wet core drilling is the necessity of finding or supplying an ample water source. The slurry formed from the mixture of water and concrete dust can be substantial. This slurry has the potential to deeply penetrate and become challenging to remove once dried. If employing the wet core drilling method, it's imperative to have effective means to swiftly contain and collect the slurry.

Dry Core Drilling: Dry core drills share similarities in appearance and operation with wet drills, but they don't employ any lubricating water. Despite the absence of water, they still extract the core with similar efficiency to wet drills. Nevertheless, the lack of water leads to higher stress and pressure on the cutting blade, affecting drill speed and service life due to accelerated impact.

Wet core drills are frequently the preferred choice across various applications. However, situations where additional water is unnecessary or might pose hazards call for dry core drilling. For instance, when working near electrical wires, a dry core drill could be the better option. It's important to note that dust is more likely to be generated with dry core drill bits due to the absence of water. Implementing dust containment measures is crucial to ensure the safety of operators and bystanders in the vicinity.

Using the Core Drill:

  1. After completing the aforementioned steps, you are prepared to operate the core drill. During this phase, follow these instructions:
  2. Verify hole alignment by lowering the bit using the feed handle until it's about 1/2 inch above the concrete. Ensure the bit isn't resting on the concrete when initiating the core drill.
  3. Always refer to the manufacturer's recommended drill speed.
  4. Keep all body parts clear of the core drill's moving components while it's in operation.
  5. When you're ready, activate the water supply to provide a gradual and even flow of water.
  6. Switch on the drill rig's power supply. Ensure that both the bit and rig operate smoothly, without any wobbling, shaking, or irregular movements.
  7. Begin lowering the bit slowly. A slower approach is better to avoid damaging the bit's cutting teeth and to allow them to engage the surface gradually.
  8. As you continue cutting, lower the bit further. Pay close attention to the rig's motor sound to ensure it's not under excessive stress. If you notice the bit slowing down under pressure or a change in the motor's pitch, ease up on the bit to let it catch up.
  9. Exerting too much pressure doesn't result in faster cutting but adds unnecessary wear to the motor and cutting teeth.
  10. Periodically, raise the bit about half an inch above the uncut surface to clear debris. Then, slowly reapply pressure.
  11. Once your desired depth is reached, start removing the bit while it's still in motion. This action aids in further clearing the hole and prevents the bit from getting stuck.
  12. Upon clearing the hole, turn off the rig. Swiftly clean up any dust, slurry, and debris. Don't allow these materials to remain, as they can embed into the surrounding surface and become difficult to remove later.
  13. Detach the rig. Remove the anchor bolt and fill the anchor bolt hole with grout.
  14. Inspect the bit and cutting teeth for any signs of damage or wear.