Why Scan Before You Core: Avoiding Rebar & Post-Tension Strikes

Why You Should Scan Before Coring Concrete

You should scan before coring concrete because a core bit can’t see the rebar, post-tension cables, live conduit and plumbing buried in the slab. A few minutes of ground penetrating radar maps those targets, marks them on the surface, and lets the driller shift the hole clear of steel and services before the bit touches concrete.

Every deck, wall, and elevated floor hides something. Rebar mats, electrical conduit, plumbing, data lines, and post-tension cables all live inside concrete you cannot see into. Drilling first and hoping for the best is how crews cause injuries, blow through budgets, and shut down occupied buildings.

The Real Cost of a Rebar or Post-Tension Strike

Not every strike is equal. Clipping a bar of rebar is annoying; severing a post-tension cable or a live feeder is dangerous and expensive. Here is what is actually on the line when nobody scans first:

• Post-tension cables: these strands sit under enormous stored tension. Cut one and it can release violently, injure the operator, and weaken the structural slab — repairs typically require a structural engineer and can stall the whole project.
• Live electrical: boring into an energized conduit risks electrocution, arc flash, and a building-wide power outage on an occupied site.
• Plumbing, gas, and data lines: a nicked pipe means flooding or a leak, and a severed data trunk can take a business offline for days.
• Rebar: even a “minor” hit dulls or destroys the core bit, slows the job down, and can compromise the reinforcement the slab depends on.

A scan that takes minutes is cheap insurance against any one of those outcomes. That is the whole reason our crews treat scanning as step one, not an add-on.

How a Pre-Core Scan Actually Works

Scanning ahead of a core is quick and non-destructive. There is no dust, no demolition, and no downtime for the space around the hole. Here is the sequence our technicians follow:

• Confirm the exact location and diameter of every proposed core hole.
• Grid the area and roll the GPR antenna across the surface in overlapping passes.
• Mark rebar, conduit, and cables directly on the slab with crayon or paint.
• Record the depth and layout of each target, then confirm a clear path or shift the hole a few inches to dodge one.

The result is simple: a marked-up slab and a clear go / no-go for the driller. If you want to understand what those markings mean, our walkthrough on making sense of a scan report breaks it down. For how radar stacks up against X-ray and buried-service locating, see our comparison of the main detection methods.

Anchoring Scans vs. Full-Penetration Scans

Not every job needs the same depth of read, so we match the scan to what you are drilling.

An anchoring scan is shallow. When a trade is setting anchors or drilling only a few inches deep, we just need to clear the top rebar mat and any near-surface conduit. It is fast and precise.

A full-penetration scan is for when you are coring all the way through a slab or wall. Here we read both faces where possible, map every layer of steel, and flag post-tension tendons before the bit ever touches concrete. Full-depth core drilling — what the public often searches as concrete drilling — is exactly where scanning earns its keep. On congested sites we can also pair the scan with private utility locating to trace services running up into or out of the slab. For buried services outside the building, Ontario law requires a free locate request through Ontario One Call before any excavation.

Where Our Crews Scan Before Coring

CDS has operated out of one Hamilton headquarters since 1967, and our mobile scanning and drilling crews travel across Ontario from that base. We regularly scan and core for contractors throughout our home city of Hamilton, across the Toronto core, and around the Niagara region — same crews, same scan-first process, wherever your slab happens to be.

See all our concrete services.

Frequently Asked Questions

Do I really need a scan before every core hole?

For any structural slab, elevated deck, or post-tensioned floor, yes — the one hole you skip is the one that finds a cable. On plain slab-on-grade with no embedded services a scan may be optional, and our crew will tell you honestly when it is and is not warranted.

How long does a pre-core scan take?

For a handful of holes, scanning usually adds minutes rather than hours. It is a small, non-destructive step that happens right before the core bit goes in, so it rarely affects your schedule.

Can GPR actually find post-tension cables?

Yes. Ground penetrating radar picks up the tendons and ducts of a post-tension system alongside rebar and conduit, so we can map them and steer the hole clear before any drilling starts.

What happens if you hit rebar while coring?

A light touch dulls the bit and slows the job; a solid strike can destroy the bit and weaken the slab’s reinforcement. Scanning first lets us reposition the hole and avoid the steel entirely.

Planning a core hole and want it done right the first time? Call CDS at (905) 529-6029 or request a free quote, and we will scan before we core.