Concrete Scanning Before Core Drilling:
The Florida Contractor's Safety Guide

In Florida's construction market, core drilling is one of the most common — and most hazardous — operations performed on concrete. Whether you're installing a drain in a bathroom slab, running conduit through a parking deck, or mounting a structural anchor in a commercial building, drilling blind into concrete is never acceptable practice.

This guide explains exactly why concrete scanning before core drilling is essential, what GPR detects, what happens when you skip it, and how to choose the right scanner for your project.

Why Florida Is a High-Risk Environment for Core Drilling

Florida's building stock presents a unique hazard profile for concrete work:

• Post-tension slabs are everywhere. From Miami Beach towers to Naples luxury condos, PT construction dominates Florida's multi-story residential and commercial market. PT cables are tensioned to 30,000+ PSI — cutting one causes immediate, violent failure.
• Conduit density is high. Florida's electrical, plumbing, and data infrastructure is often embedded in or beneath concrete slabs, particularly in commercial buildings built from the 1970s onward.
• Renovation rates are high. Florida's aging building stock is constantly being renovated — every renovation project is a potential encounter with hidden infrastructure.
• As-built drawings are unreliable. Even when drawings exist, they rarely reflect field changes made during original construction. The only reliable method is scanning the actual slab.

What GPR Detects in Concrete

Ground penetrating radar works by transmitting high-frequency radio waves into concrete and measuring the time it takes for reflections to return from subsurface objects. The following can be detected:

Rebar

Reinforcing steel appears as hyperbolic signatures in GPR data. Rebar spacing, depth, and orientation can be determined with precision using modern systems like the GSSI StructureScan Mini XT or the GSSI NC 3D Scanner (which produces a full plan-view map).

Post-Tension Cables

PT cables are smaller in diameter than rebar but still detectable by GPR. High-frequency antennas (2700 MHz) provide the resolution needed to distinguish PT cables from rebar and conduit. A trained operator can identify the characteristic undulating profile of unbonded PT tendon profiles.

Conduits and Pipes

Metallic and non-metallic conduits embedded in concrete slabs are detectable by GPR. Electrical conduit, plumbing sleeves, and HVAC piping can often be traced across a scan area to understand their routing before drilling begins.

Voids and Delaminations

Subsurface voids, honeycombing, and areas of concrete delamination — which can cause core drill bits to grab and break — are also detectable in GPR data, though this requires experienced data interpretation.

How to Scan Correctly Before Core Drilling

Scanning correctly is not simply about having the right equipment — it's about methodology. Here's the correct process:

1. Define the Drill Zone

Mark the intended drill location. Scan a minimum of 12–18 inches in every direction from the target point — you need to know what's around the hole, not just directly below it.

2. Scan in Two Perpendicular Directions

Always scan in both X and Y directions across the drill zone. Scanning in one direction only can miss objects running parallel to your scan lines. Grid scanning provides a complete picture.

3. Mark What You Find

Use chalk or marking paint to mark rebar, PT cables, and conduits on the slab surface at the correct scale. This creates a visual guide for the driller.

4. Identify a Safe Drill Window

Select a drill location that provides adequate clearance from all detected objects — typically a minimum of 1.5 inches from any PT cable or rebar. Confirm the window is large enough for your core bit diameter.

5. Document and Communicate

Photograph the marked scan area and communicate findings to the core drill operator before work begins. On complex or high-risk jobs, provide a written scan report.

Which GPR Scanner Is Right for Your Core Drilling Project?

• GSSI StructureScan Mini XT ($350/day) — Best all-around choice for standard core drilling locations in residential and commercial slabs up to 18 inches depth.
• GSSI NC 3D Scanner ($550/day) — Best for PT slab scanning where you need a visual plan view of the entire slab grid. Ideal for high-risk, high-consequence drill locations.
• GSSI 2300 MHz Palm XT ($390/day) — Best for wall scanning, thin slabs, and locations where a compact scanner is needed in tight spaces.
• GSSI Flex 15 Antenna ($350/day) — Best for deep slabs (18+ inches) or heavily reinforced concrete where standard antennas lose signal.

Florida Case Example: Skipping the Scan

On a Miami Beach renovation project in 2023, a subcontractor drilled without scanning a 1980s-era parking deck slab. The core bit struck an unbonded PT tendon at approximately 4 inches of depth. The resulting cable failure cracked a 6-foot section of the slab and caused a two-week project shutdown while structural engineers assessed the damage. Repair and delay costs exceeded $85,000.

A 30-minute GPR scan using a GSSI StructureScan Mini — rentable for $350/day — would have prevented the incident entirely.

When to Hire a Scanning Service vs. Renting Equipment

Renting GPR equipment is the right choice when your crew has (or can quickly acquire) the skills to operate it. For one-time projects or complex scanning requirements, hiring a concrete scanning service may be more efficient. See our comparison: GPR Rental vs. Hiring a Scanning Service in Florida.

For teams that want to develop in-house scanning capability, our Concrete Scanning Training course — offered statewide in Florida — teaches exactly these techniques with hands-on practice on real concrete.