How to Install Bollards in Existing Concrete (Core-Drill Method)

Installing bollards in existing concrete uses the core-drill retrofit method: cutting a clean cylindrical hole through the slab and seating the bollard with non-shrink structural grout or anchor epoxy. The process avoids breaking up the surrounding concrete, takes 45 to 75 minutes per bollard, and requires careful rebar avoidance to keep the slab structurally sound. Cojo retrofitted eight pipe bollards into a 30-year-old Portland warehouse loading dock in March 2026 using this method without breaking out a single panel. This guide walks through the equipment, the cuts, and the seating process step by step.

For the broader install reference, see How to Install Bollards. For new-pour fixed installs, see How to Install a Fixed Bollard. For category context, see our What Are Bollards hub.

When Is Core-Drilling the Right Method?

Core-drilling is the preferred retrofit method when:

• Existing concrete is at least 6 inches thick.
• The bollard does not need to be K-rated.
• Rebar can be avoided in the cut location.
• The site is occupied or active enough that breaking out concrete panels is disruptive.

For K-rated installs, the certified configuration almost always specifies foundation excavation rather than core retrofit. The U.S. State Department SD-STD-02.01 crash-rating spec sheets reference engineered foundations, not retrofits, for K4 through K12 ratings.

What Tools and Materials Do You Need?

A core-drill retrofit needs purpose-built equipment that is harder to rent than the surface-mount kit.

• Wet-cutting core drill -- gas or electric, 6-inch to 8-inch capacity (rental $90 to $250 per day in Oregon)
• Diamond core bit, 6-inch or 8-inch diameter (rental $40 to $120 per day, or buy-and-resell)
• Continuous water supply -- garden hose or pump
• Wet vacuum or shop vac for slurry containment
• Rebar locator (electromagnetic or ground-penetrating radar)
• Non-shrink structural grout -- Sika 212, Quikrete Non-Shrink Precision, or equivalent
• Mixing paddle and 5-gallon buckets
• Plumb laser or 4-foot bubble level
• Personal protective equipment per OSHA 29 CFR 1926.1153 silica standard

The OSHA silica rule under 29 CFR 1926.1153 mandates dust controls for any concrete cutting operation. Wet-cutting satisfies the rule on most jobsites, but a written exposure control plan is still required.

Step 1: Why Locate Rebar Before Drilling?

Cutting rebar reduces slab integrity. A typical 6-inch reinforced slab uses #4 rebar at 12-inch centers each way. Striking rebar with a 6-inch core bit destroys the bit and -- more importantly -- creates a stress concentration in the surrounding concrete.

How to Find Rebar Without GPR

A magnetic rebar locator like the Bosch D-Tect or Hilti PS-50 maps rebar positions to within 1/4 inch in standard slab thickness. Lay out the proposed bollard pattern, then walk the locator over each position. Mark rebar with chalk. Slide the bollard pattern 4 to 8 inches in any direction to clear the rebar grid where possible.

For deep slabs or post-tensioned concrete, ground-penetrating radar is the only safe option. GPR rental runs $400 to $800 per day; for any slab thicker than 8 inches or any structure where post-tension cables may be present, this is a non-negotiable line item.

Step 2: How Do You Wet-Core a Bollard Hole?

The core drill is anchored to the concrete with a vacuum baseplate or a single-anchor stand. Vacuum baseplates require smooth concrete; cracked or rough surfaces need the anchor stand.

Setting the Cut

Position the drill so the bit centerline aligns with the marked bollard center. Verify plumb -- a tilted core hole means a tilted bollard. Start water flow before the bit contacts the concrete.

Drilling the Cut

Apply slow, steady pressure. Modern core bits cut at 50 to 200 RPM depending on diameter. Cutting time for a 6-inch bit through 8 inches of concrete runs 15 to 30 minutes. Listen for chatter that indicates the bit is rocking; correct stand alignment if it occurs.

Removing the Core

The cut produces a solid cylindrical core that comes out in one piece if the cut went all the way through. If the bit hit rebar, the core may break in two pieces. Either way, lift the core out with a hook or pipe wrench gripping the cut edge. The hole is now ready for the bollard.

Step 3: How to Seat the Bollard with Grout

Non-shrink structural grout is the standard product for filling the gap between the bollard pipe and the cut concrete edge.

Pre-Wetting the Hole

Saturate the cut concrete surface with water for 30 minutes before grouting. Dry concrete pulls water from fresh grout, which weakens the cure. Drain standing water before pouring grout.

Lowering and Plumbing the Bollard

Lower the bollard into the hole. The bollard should bottom out 2 to 4 inches above the bottom of the hole to allow grout under the base. Verify plumb on two perpendicular faces. Wedge with shims or wood blocks at the top edge to hold position.

Pouring the Grout

Mix grout per manufacturer instructions. Pour around the bollard in lifts of 4 to 6 inches, working a thin steel rod around the perimeter to release air pockets. Top off flush with the surrounding concrete or slightly crowned to shed water. The American Concrete Institute ACI 351.1 covers grouting practices for equipment foundations and is the reference document for this work.

Step 4: How Long Does the Grout Have to Cure?

Cure time depends on the grout product and ambient temperature. Typical specifications:

Time	Compressive Strength	Allowed Activity
4 hours	1,500 psi	Light foot traffic only
24 hours	4,000 to 5,000 psi	Pedestrian traffic
72 hours	6,500 to 7,500 psi	Slow vehicle contact
7 days	8,000+ psi	Full traffic exposure
28 days	9,000+ psi	Full design strength

Cold-weather installs (below 50 degrees F) extend cure times by 50 to 100%. Hot-weather installs (above 90 degrees F) require water curing or curing compound to prevent surface cracking.

What About the Cut-Concrete Slurry?

The wet-cutting process generates concrete slurry -- a mix of water and cement fines -- that is alkaline and must not enter storm drains. The U.S. EPA Construction General Permit under the Clean Water Act NPDES program treats concrete slurry as a regulated discharge.

Capture slurry with:

• Wet vacuum during cutting
• Berms of straw wattle or sand bags around the work area
• Dewatering bag for collected slurry
• Off-site disposal at a licensed concrete recycler

For maintenance after install, see our bollard curb stop painting service guide. For Portland metro retrofit work where Cojo handles a lot of this method, see Bollard Installation Portland.

Get a Retrofit Install Quote

Core-drill bollard installation in existing concrete requires specific equipment and rebar awareness. The cost difference between a well-executed retrofit and a botched cut that compromises the slab is significant. Cojo handles core-drill bollard retrofits across Oregon, including warehouse loading docks, retrofit storefronts, and existing parking-lot installations. Contact Cojo for a site assessment and retrofit quote.

---