What is GPR concrete scanning?

GPR (ground-penetrating radar) scanning is a non-destructive way to "see" what's inside a slab or wall before anyone cuts or drills into it — rebar, wire mesh, conduit, post-tension cables, voids, and slab thickness. It's the step that happens before the saw or the core rig ever touches the concrete.

Why it matters

Concrete slabs and walls routinely hide things a crew can't see from the surface: steel rebar or wire mesh, electrical conduit, plumbing lines, and in many commercial and some residential slabs, post-tension (PT) cables — steel tendons stressed and locked under load to hold the slab together. Cutting or coring blind can strike any of these. Hitting rebar or conduit ruins bits and can damage the embedded utility. Striking a live post-tension cable is a different order of problem: the cable is under stored tension, and a cut one can release that tension suddenly, which is genuinely dangerous to anyone nearby and expensive to repair. Scanning first is how a shop avoids finding any of this out the hard way.

How it works

A technician rolls a GPR antenna across the surface of the slab or wall in a grid pattern. The unit sends radio waves into the concrete and reads what bounces back — dense objects like steel and voids reflect the signal differently than plain concrete, and the software maps those reflections in real time. The technician marks the surface directly (or logs it digitally) to show where it's clear to cut and where an embedment sits, so the crew that cuts or cores knows exactly where — and where not — to go.

When it's required

Any core or cut into a structural or post-tensioned slab should be scanned first, no exceptions. The same goes for work near known or suspected utilities, and most commercial and parking-structure jobs where PT construction is common. On a simple, shallow residential cut with no post-tension and no nearby utilities, the risk is lower — but it's still the shop's call to make, not a guess.

Who does the scanning

Some concrete cutting and coring shops run GPR themselves, in-house, as part of the job. Others bring in a dedicated scanning specialist for larger or higher-risk jobs, then cut once the scan clears the path. Either is normal — what matters is that the scan happens before the concrete does, by someone who knows how to read the results.

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GPR scanning FAQ

How accurate is GPR at finding rebar and post-tension cables?
In normal, dry concrete, GPR reliably locates rebar, wire mesh, and post-tension (PT) cables, and gives a solid read on slab thickness. Accuracy drops in a few known conditions: very wet or heavily reinforced concrete, congested rebar mats, or unusually deep targets can scatter the radar return. GPR is a mapping tool, not an X-ray — it shows what's in the scan path, not a full internal image, so an experienced operator interpreting the data matters as much as the equipment.
Is GPR scanning always necessary?
Not for every cut. A shallow cut in a simple residential slab with no known post-tension or utilities is lower-risk. Scanning becomes necessary — not optional — for anything in a post-tensioned or structural slab, any core or cut near known or suspected utilities, and commercial or parking structure work where PT cables are common. When in doubt, ask the shop whether the job needs a scan; most will tell you honestly.
How is GPR scanning priced?
Some shops fold scanning into the price of the cut or core, especially on small residential jobs. Others charge a separate scan fee — flat per-visit, or per area scanned — particularly on commercial jobs or when a dedicated GPR specialist is brought in. There's no standard number; ask for it broken out on the quote so you know whether it's included.
GPR vs. concrete X-ray — what's the difference?
Both locate embedments before cutting, but they work differently. GPR is single-sided — the operator only needs access to one face of the slab or wall — uses radio waves, and involves no radiation, so there's no site evacuation or radiation safety perimeter. Concrete X-ray (radiography) generally needs access to both sides and does involve radiation, which means a cleared safety zone and more setup time. GPR is faster and more common for routine scanning; X-ray is sometimes used where GPR results are ambiguous or an especially detailed image is needed.

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