Long-form guide · 11-minute read
Concrete scanning. Everything inside the slab, before the first cut.
Every core hole, saw cut, and anchor bolt is a gamble until someone images what's inside the concrete. This guide covers how GPR concrete scanning works, what it finds (rebar, post-tension cables, conduits, pipes, voids), how accurate it is, what it costs in BC, and the 15-tonne reason post-tensioned slabs make scanning non-negotiable.
What is concrete scanning?
Concrete scanning is the non-destructive imaging of everything embedded in — or hidden beneath — a concrete slab, wall, or beam. A high-frequency (1.6 GHz) ground-penetrating radar antenna is passed over the surface in two directions; reflections from rebar, post-tension cables, electrical conduits, in-slab pipes, and voids are interpreted in real time and marked directly on the concrete.
The job it replaces is guessing. Before scanning became standard practice, crews cored where the drawing said it was clear — and the drawings were wrong often enough that severed conduits, cut rebar, and struck post-tension cables were treated as a cost of doing business. On a post-tensioned slab that cost can be catastrophic: each tensioned strand carries roughly 15–20 tonnes of force, and cutting one can eject hardware through the slab edge at lethal speed while stripping the bay of design capacity.
Modern practice is simple: nothing penetrates structural concrete until the location is scanned, the embeds are marked, and a clear window is identified. The scan takes 15–30 minutes per location; crews drill the same visit. In BC — where most towers and parkades poured since the early 1970s are post-tensioned — assume PT until imaging proves otherwise.
When you need concrete scanning
If you're seeing any of these signs, professional detection is warranted:
- Coring or saw-cutting planned on any suspended slab
- Anchoring equipment or seismic bracing into structural concrete
- Building age/type suggests post-tension construction (BC towers post-1970)
- No reliable as-built drawings for the slab
- Drummy or soft spot in a floor (possible sub-slab void)
- Parkade deck showing efflorescence, rust staining, or delamination
- Slab thickness must be verified against structural drawings
- Electrical or mechanical trades roughing-in through existing floors
One scan costs hundreds. One strike costs tens of thousands.
A severed feeder in an occupied building means an electrician, an outage, possibly fire-watch, and schedule slip — $5,000–$50,000 is routine. A cut post-tension cable means engineered repairs, possible injury, and a slab bay out of service — commonly $20,000–$75,000+. The scan that prevents either is a few hundred dollars and 20 minutes. No other line item on a construction budget has this risk-to-cost ratio.
How we detect it
- 1
Scope the penetrations
Core, cut, and anchor locations are listed with the trades; building age and slab type flag post-tension likelihood before anyone mobilises.
- 2
Scan each location
Two-direction 1.6 GHz passes at every penetration point image rebar mats, PT cables, conduits, and pipes with depth estimates.
- 3
Distinguish the targets
PT cables run in draped profiles at characteristic spacings; rebar sits in regular mats; conduits read at distinct depths. An experienced analyst separates them reliably — this is interpretation skill, not just hardware.
- 4
Mark clear windows
Embeds are painted in one colour, safe penetration windows in another, photographed for the record. Obstructed points get the nearest safe offset.
- 5
Drill same visit
Crews typically drill immediately against the marks. For congested zones we stand by, re-scanning offsets in real time as cores advance.
- 6
Document
Scan imagery, depth tables, and marked photos per location — the diligence record engineers, GCs, and insurers expect on file.
Detection technologies we use
GPR Concrete Antenna (1.6 GHz)
The core tool — high-resolution imaging to ~45 cm depth, resolving targets 5 cm apart.
Learn morePost-Tension Cable Mapping
Specialised survey distinguishing draped PT profiles from rebar mats before any penetration.
Learn moreElectromagnetic Detection
Pairs with GPR to flag energised conduits — radar finds the conduit, EM senses whether it's live.
Void & Thickness Profiling
Same antenna, different question: sub-slab voids and ±5 mm thickness verification.
Learn moreCommon scenarios
Tenant improvement (office tower)
A 28-location coring scope for mechanical and electrical rough-in cleared in one morning. Three locations sat over PT cables and were offset 15 cm on the spot — zero strikes, zero schedule impact, drilling completed the same day.
Strata parkade
A soft-sounding drive lane was scanned before barricading decisions: a 4 m × 2 m sub-slab void mapped under 90 mm of remaining bridge. The area was coned the same hour and repaired on schedule instead of becoming a collapse.
Seismic upgrade (heritage)
Anchor layouts for bracing in a 1928 building were scanned against unknown reinforcement. The original bar layout — nothing like the archive drawings — was mapped and the engineer relocated 40% of anchors before fabrication, not after.
Typical pricing
Typical range. Final price quoted on the free phone consult.
- Single-visit clearance (1–5 locations): typically $350–$500.
- Multi-point TI scopes (10–40 locations): typically $500–$1,500.
- Full-slab surveys, parkade condition programs: quoted by area.
- Same province-wide pricing across all 47 BC cities we serve.
Frequently asked questions
What does concrete scanning find?
Rebar mats, post-tension cables, electrical conduits, in-slab water and heating pipes, voids beneath or within the slab, and slab thickness — essentially everything a drill bit could hit or an engineer needs to know about, imaged from one side with no damage.
How accurate is GPR concrete scanning?
Embedded targets locate within about ±5 cm horizontally, with depth estimates around ±10%. Targets as close as 5 cm apart resolve separately at shallow depth. Every penetration point is scanned individually rather than extrapolated from a sample area — accuracy claims only matter at the exact spot the bit lands.
Can scanning tell rebar from a post-tension cable?
Yes — reliably, in experienced hands. PT cables run in draped (curved) profiles at characteristic spacings and depths; rebar sits in flat, regular mats. The signatures differ, and we mark them differently on the slab. When a building's age makes PT plausible, every ambiguous target is treated as a cable until proven otherwise.
Is concrete scanning the same as concrete X-ray?
No. GPR scanning needs one surface, no radiation, no evacuation, and delivers marks in minutes — but resolves to about ±5 cm. X-ray needs both slab faces and an evacuated exposure area, costs several times more, and is physically impossible on slab-on-grade — but resolves sub-centimetre detail in congested embeds. Roughly 95% of BC jobs are GPR jobs; see our full GPR-vs-X-ray comparison.
How deep can the scan see?
About 45 cm into concrete with the 1.6 GHz antenna — which covers nearly every slab, topping, and wall in BC construction. Thicker mass-concrete elements are handled with lower-frequency antennas at reduced resolution.
What does it cost in BC?
Single-visit clearance scans typically run $350–$500; multi-point tenant-improvement scopes $500–$1,500; area surveys by quote. Pricing is identical across all 47 cities we serve — the free phone consult (604-239-9934) turns a location count into a firm number in five minutes.
How long does it take?
15–30 minutes per location including marking and photos. A 20–40 point TI scope clears in a half day to a day. Crews drill the same visit — there is no report-waiting period for routine clearance work.
Can you scan walls and ceilings?
Yes — the concrete antenna works on any orientation. Wall penetrations for sleeves and ceiling anchors for mechanical hangers are everyday scans, and the underside of suspended slabs is checked where hung services add strike risk.
Do engineers accept scan reports in place of X-ray?
For locating and clearance purposes, yes — structural engineers across BC routinely condition coring permission on a GPR scan report. Marked photographs plus depth tables per location is the format they expect. X-ray only enters when sub-centimetre identification of congested embeds is genuinely required.
Is the equipment safe in occupied buildings?
Completely — GPR emits less radio-frequency energy than a phone. No evacuation, no permits, no interference with hospital, lab, or office equipment. Scanning during business hours in occupied space is routine.
What about voids under the slab?
Voids reflect distinctively and are boundary-mapped, with remaining slab-bridge thickness measured — the number that decides between monitoring and immediate barricade. Leaking pipes are the most common cause, which is why our void work and leak detection often run as one investigation.
Do you serve my city?
All 47 BC cities in our coverage — Metro Vancouver through the Island, Okanagan, Kootenays, and Northern BC — at the same pricing. Six concrete services have dedicated pages for every city; start at the concrete scanning hub and pick your city.
Related guides & services
Concrete Scanning Hub (12 services)
Every concrete service + 47-city coverage
Compare: GPR vs X-Ray
The honest 95/5 answer
Post-Tension Cable Mapping
Core Drilling Safety Scanning
Slab Leak Detection Guide
GPR Pillar Guide
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