RESOURCES - Core Drilling, Rock Drilling, and Grouting

Objective: By mastering this lesson, you will be able to core drill and rock drill into existing surfaces. Then mix and pour grout.

Key Questions:

What must you know when using Quik-Rock or other fast setting grout?
How deep and how wide do we need to drill?
How to pour grout around a post.
Quoting core drilling or rock drilling is a two way street.
How to rock drill.
How to core drill.

What you need to know when using Quik-Rock or other fast setting grout?

Perfect temperature is 70 degrees.
Add cold water if warmer and hot water if colder.
Never use quick-rock in temperatures below 30 degrees.
If using more than five pounds of grout, mix vigorously with mechanical means such as powered blender.
Pour grout within five minutes of initial mix.
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.

Below is the Quik-Rock mixing guide. If posts larger than 3”, make sure hole is 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:

Quik Rock : Portland : Gravel.

Use as little water as possible but enough to establish flow. Too much water breaks down grout.

If using Qui-Rok as an additive to concrete, hole should be three times the diameter of the posts. 3” post would require 9” diameter.

To improve your success while using Quik-Rock, perform these additional steps:

Add key ways into the post by cutting slits into the post. This will significantly increase 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.
Widen your gap between post to allow materials to flow all around post.

How deep and how wide do we need to drill?

Only because we do not specify or understand how far to drill/core; we attempt to drill/core to the center of the earth. The truth is that drilling/coring beyond what is required does not bring additional benefit but only additional cost. For the sake of this educational moment, we will conclude that when referring to core drilling that we are also referencing rock drilling where applicable.

Drilling does not have to continue until you reach dirt or mother earth. It is ok to not go all the way to the bottom of the slab. The earth will not stop spinning. According to ASTM F 567…

For a 2 ½” diamater post, we only need to drill to a depth of 7 ½”.

2.5” post diamater x 3 = 7.5” depth

This is actually 1 ½” deeper than what is required by the Federal Specification RRF-191 which states a depth of 6”. Bear in mind that we are tying into the slab. Doing so, the post will only give/fail if the slab fails. No further footing is necessary.

In accordance with ASTM 567 and standard practice, it is not necessary to keep drilling. Only a few more inches and we will hit the bottom. That is not always the case and those additional inches cost time and materials.

How to pour grout around a post. Leave at least a ½” void all around the post so that the grout may flow freely to fill the void. For a 2 ½” post, use a 3 ½” rock drill bit or core drill.

TIP:

When mixing grout, cut the top of the pop bottle or whatever container you are mixing in at a 45 degree angle. This will allow you to tip the container and still pour the grout in the void.
Place your post in the cored hole. Make sure it is to the proper height.
Use three small wood shims to level the post in the hole
Mix your grout in accordance to manufacturers' specifications. The initial mix should be the consistency of a good milk shake.
Pour the mix around the post and assure it fills-in all voids. Leave your pour about 5/8” down from the top of your finished grade.
Let the grout set-up and remove the shims.
Mix another batch of grout. This time it should be less consistent. Somewhere between a milk shake and milk.
Pour this final mix in and around the post so that it is slightly higher than the finished grade to be sure to shed water. The less than milk shake consistency will provide a smooth even finish on top.
If working with decorative, colored or stone surfaces, cut out the bottom of a plastic bag. Place the bag into the hole so that the sides of the bag are about a ½” into the hole with the rest of the bag folded over the top and flat on the surface. Pour your grout per the above. When finished, use a razor knife to cut around the edge of the bag where it meets the surface. The folded over bag will catch any over pour or drips and can then be discarded.

Core drilling and rock drilling is not indefinite

It should not only be measured by diameter but also by depth. When estimating a project that includes drilling; you must consider the depth of the material that you will be coring or drilling. The below illustration demonstrates the standard thickness of paving based on use. This is a good rule of thumb. This does not apply to asphalt. Most asphalt slabs are less than six inches but it may vary considerably as additional lifts are placed over time. It is not unusual to find asphalt slabs over one foot thick.

Quoting core drilling or rock drilling is a two-way street. Not only do we have to specify to our customer the depth of our cores but we must also specify to our installation crews. Unfortunately, our installers have a bad habit of drilling until oil or dirt is found. Our sales and supervisory staff must communicate 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.”

What is rock drilling? Rock drilling is a jackhammer-like tool that both hammers and spins. It is used predominately in concrete and like-kind surfaces. It is designed to both pulverize and then remove the area being impacted. It is not cutting it is busting up the surface.

A rock drill consists of the body, shaft, and bit. A large CFM compressor connects to the body. When air is applied and the trigger is pulled the shaft and bit attached begin to spin and hammer. Air is sent down the center of the shaft and through the bit to blow out dust.

How to operate a rock drill.

Be sure you have proper PPE equipment that includes safety glasses, ear protection, and steel-toed boots.
Mark out all your holes.
Mark the shaft of the drill bit to the desired depth.
Connect the drill to a large CFM compressor. Be sure you have properly connected all hoses with safety whips at each connection point.
Be sure hoses pass through inline oiler and oiler is filled with oil. Test to be sure oil is being dispensed through the hoses by placing a white sheet of paper at the end of the hose under pressure to test the spatter of oil on the sheet. You should see a consistent light pattern of oil.
Screw the tip onto the shaft. The threads are reversed.
Mark the shaft to the desired depth you intend on drilling.
Release the lever where the shaft inserts. Insert the tipped shaft into the rock drill and engage the lever to capture the shaft.
Be sure the drill is set to the off, release, position. Start the compressor.
Check all your hose connections to be sure you do not have any kinks, loose connections, leaks and whips are placed at each connection.
Stand the drill up and place the bit over the marked location. The drill should be set centered between your legs and shoulders. Slowly engage the drill while applying some pressure so the drill does not bounce around.
You may use your feet to brace the drill bit to keep it centered. In doing so, make sure you have steel-toed work boats and you operate the drill at a very slow speed. Too much air speed and the drill will begin to bounce and may bounce on top of your boot.
Once the drill has centered itself and drilled an initial outline of your hole, you may allow the drill to run at a higher speed and apply less down pressure.
Applying less down pressure will allow the drill to bit to move up and down and spin around, pulverizing the surface area. This will also allow the air traveling down the center of the shaft and bit to blow out any debris.
Drill only to the desired depth. Disengage the drill. Pull from the hole.
Check your holes for desired depth and good consistency.
Remove any remaining dust and debris. This is critical. If we place the grout with dust lining the side of the hole, the grout will bind to the dust and not to the side of the hole.

What is core drilling?

Core drilling is the process of removing a cylinder of material using a hollow cylindrical drill. Core drilling is used in construction industries, mining industries, geotechnical engineering and research. Core drills are useful not only to cut a hole in material, but also in extracting material so that it can be examined. The core drill has three main parts, comprising a motor, a handle, and the bit.

How Does a Core Drill Work?

A diamond concrete drill bit is required for concrete core drilling. The bits for these tools are essentially steel tubes impregnated with pieces of industrial diamond. This drill is mounted onto the drilling machine’s shaft and then secured to the structure you are drilling into. Once the core drill has completed the drilling process, there will be a concrete “slug” — the core — inside the drill bit that you can extract from the hole. This is accomplished by the drill’s hollow center, so it keeps the slug inside that defined area until removal. Core drills can also cut through several other materials besides concrete, including porcelain tile, limestone, rock, granite, fiberglass and even ice.

Preparing the job site.

Prepare the core drill and job site.
Before actually operating the core drill, it is important to prepare the job site and ensure the drill is ready for use. You will want to:
Check for alignment and possible binding of moving parts, mounting, and any other conditions that may affect core drill operation. Do not use the core drill if it shows any signs of damage.
Read and fully understand the operating manual.
Check the power supply’s flow and pressure output against the core drill’s requirements.
Check for live electrical wiring near the work site or embedded in the material being drilled.
If drilling through a wall, check both sides for possible obstructions.
Before drilling through a floor, provide protection for all personnel and materials below the work area. Cores generally drop from the bit at the completion of the hole.
Ensure all personnel is using the appropriate safety equipment.
Clear the working area of all unauthorized personnel. Place barricades or secure the area so that no person can be injured.

Anchoring a core drill

A core drill can typically be bolt anchored or ceiling jack anchored to the floor or bolt anchored to the wall.
Measure the distance from the center of the anchor bolt slot in the base to the center of the drill spindle.
Mark from the center of the hole on the floor to be drilled to the spot where the anchor bolt hole will be drilled.
Drill and set the anchor bolt. Then place core drill over anchor hole and hand tighten the bolt.
Secure the core drill by tightening the anchor bolt.
Verify with your customer before anchoring that you may drill anchor holes next to each hole to be cored. These anchor holes will remain upon and should be filled with grout. Make customer aware these holes will be visible upon completion of project. If coring in decorative stone, brick, concrete or other like-kind decorative and colored materials, it is generally understood that leaving anchor bolt holes is not acceptable.
Failing to not properly anchoring a core drill rig may result in serious bodily harm. Drill rig motors operate at high speed and torque.

Installing a drill bit

Before installing the drill bit, ensure that neither the bit nor the core drill is hot. What’s more, always make sure to wear protective gloves when handling, installing, and removing core drill bits.
Make sure there is visible bit cutting teeth life on the bit.
Make sure the bit is not perfectly round and not oval shaped.
Make sure the bit the bit is not dented from others hammering on the side of the bit to remove the core.
Any damage to the bit and its shape will cause the bit to bind in the hole and cause the core drill rig to work harder than typical operating torque. Over time, you will burn out the winding and motor.
Next, remove any dirt or contamination that may have accumulated on either the bit or drill spindle.
Mark the side of the bit for the depth you intend on cutting.
Once you do that, you can begin to thread the drill bit onto the drill spindle and tighten it securely with a bit wrench.

Wet Drilling vs. Dry Drilling Depending on the application, workers may have to use either wet or dry core drilling.

Wet Core Drilling. Wet core drilling offers the greater efficiency of the two processes. Wet drills will typically drive the bit through the core faster than dry drill bits because the lubrication of the water helps loosen the material’s surface. Wet core drilling also leaves behind a cleaner, more stable hole surface because the water minimizes the dust produced during drilling. Concrete, soft or hard brick, and reinforced concrete are materials best suited for wet core drilling. Core drill bits that run wet will typically offer a longer life span than dry-running bits, as the water acts as acoolant for the heat produced during operation. The speed of the work itself also plays a role in bit durability. The downside to wet core drilling is finding or supplying an adequate water source. The slurry created from the combination of water and concrete dust is significant. It generates a great deal of slurry that can quickly impregnate the surrounding surface and when left to dry be almost impossible to remove. If using a wet core drill method, make sure you have the necessary means to quickly contain and collect the slurry.

Dry Core Drilling

Dry core drills look and operate very similarly to wet drills, but they use no lubricant. They will still remove the core in the same capacity a wet drill does. However, because there is no water involved, there is inherently more stress and pressure on the cutting blade, affecting drill speed and service life due to accelerated impact.

Wet core drills are often the preferred choice for many applications. If extra water is not necessary or may be hazardous for a particular job, then a dry core drill can be an acceptable choice. For example, if the work involves electrical wires, a dry core drill might be a better option. One thing to remember about dry core drill bits is that the lack of water means there is more likely to be dust. You will need dust containment measures to ensure your operators and anyone nearby stays safe.

Operating the core drill

Once you have done the steps above, you are ready to operate the core drill. During this process, you will want to do the following:
Check the hole alignment by lowering the bit with the feed handle until the bit is about 1/2 inch from the concrete. It is important to ensure the bit is not resting on the concrete when starting the core drill.
Make sure to always check the manufacturer’s recommendation for drill speed.
Keep all body parts away from all moving parts of the core drill while in operation.
When ready, turn on the water supply providing a slow even application of water.
Turn on the drill rig power supply. Be sure the bit and rig are operating smoothly. There should be no wobbling, shaking or even operation.
Slowly begin to lower the bit. Slower the better so as to not damage the bit’s cutting teeth and alow these teeth to slowly engage the surface.
Continue to lower the bit as you cut. Listen carefully to the rig’s motor to be sure the motor is not being stressed. If the bit begins to slow down under pressure or you hear the pitch of the motor change, easy-up on the bit to allow it to catch-up.
By applying too much pressure, you are not cutting any faster but not causing unnecessary wear on the motor and cutting teeth.
Periodically, lift the bit about a half inch of above the uncut surface to all itself to clear the debris. Then, slowly reapply pressure.
Once you have reached the desired depth, slowly begin to remove the bit while still turning. This will allow the bit to further clear the hole and not get stuck.
Once you have cleared the hole, shut-off the rig. Clean-up any dust, slurry and debris immediately. Do not allow this dust or slurry to remain as it will impregnate the surrounding surface and prove almost impossible to remove later.
Remove the rig. Remove the anchor bolt. Fill the anchor bolt hole in with grout.
Check the bit and cutting teeth.