Concrete Scanning Before Drilling: 7 Checks for Australian Crews
Yes, you should scan concrete before you drill, core, or cut it. Ground penetrating radar (GPR), backed by complementary locators when needed, reveals rebar, post-tension tendons, and conduits before a bit finds them. A scan reduces utility strikes and feeds your Safe Work Method Statement (SWMS) and clearance decisions. We provide this as a qualified scanning and drilling contractor.
TL;DR:
- High frequency antennas resolve detail to 200–400 mm, while lower frequency units reach deeper; wet or newly poured concrete can reduce penetration.
- Metallic targets return strong reflections, but plastic conduits and other nonmetallic objects may need an electromagnetic locator, angled scan, or confirmatory core.
- Require proof behind clear to claims: reports should state penetration, and each target should be marked at three points, photographed, and matched to written findings.
- Build scanning into SWMS planning: review drawings, map drill areas, allow interpretation and marking time, then set exclusion zones and confirm RCDs and water control.
Table of Contents
- What does concrete scanning detect, and why does it matter for drilling?
- How does scanning work, and what equipment do contractors use?
- What can make a scan miss or mislead?
- When should you scan, and how does it fit into pre-drill planning and your SWMS?
- How do you read a scan report and its “clear to” language?
- What should a pre-drill checklist look like after the scan?
- Why do experience and licensed crews matter?
- Book scanning and drilling with one licensed contractor
- FAQ
- Sources
What does concrete scanning detect, and why does it matter for drilling?
A scan builds a picture of what sits inside the slab so you can choose a safe drilling position. GPR maps internal features without cutting, locating reinforcement, post-tension tendons, conduits, and voids, and it measures slab thickness. Each target carries its own consequence if you hit it:
- Rebar: spacing and cover tell you where a bit can pass, and cutting it can weaken the member.
- Post-tension tendons and ducts: a strike can release stored force and cause serious injury, so these are the highest-stakes targets.
- Electrical conduits and metallic pipes: contact risks electric shock, service outages, and damaged supply lines.
- PVC and other nonmetallic conduits: these are harder to see and are easily missed on a rushed scan.
- Voids, honeycombing, and delamination planes: these can make a hole wander, bind the bit, or fail to hold an anchor.
- Slab thickness changes: these affect how deep a core or anchor can safely go.
Confidence differs by target. Metallic objects return strong reflections, while nonmetallic ones can produce weak signals and may need a complementary locator or a confirmatory core. Depth depends on the antenna. High-frequency antennas resolve fine detail in roughly the top 300 mm, lower-frequency ones reach deeper, and the condition of the concrete affects both. For a wider explanation, see what concrete scanning is.
How does scanning work, and what equipment do contractors use?
GPR sends short electromagnetic pulses into the slab and records the reflections that bounce back at boundaries between materials. A single pass along a line produces a cross-section view, often called a B-scan. Running a grid of passes lets the operator build an area map, sometimes called a C-scan, which shows how targets lie across the whole slab. Our own write-up on why GPR scanning matters goes deeper on the principle.
Antenna frequency is a trade-off between detail and depth. High-frequency antennas of 1600–2600 MHz give fine resolution to roughly 200–400 mm, while 400–900 MHz antennas penetrate deeper with less detail. Experienced operators often combine frequencies on the same slab.
Radar is rarely the only tool on the job:
- Ferroscan: measures rebar cover and spacing in detail.
- Electromagnetic (EM) locators: trace metallic utilities, and SIM guidance names them as a complementary tool.
- X-ray: a specialized, higher-cost option where the situation calls for it.
What can make a scan miss or mislead?
Scanning is non-destructive, but it is not risk-free. Moisture and age significantly affect GPR results, and wet or young concrete can make a scan ambiguous and reduce penetration depth. Chloride contamination has a similar effect. Other common limits include:
- Dense reinforcement mesh that masks deeper targets
- Small or nonmetallic targets with weak reflections
- Signal damping in lossy concrete
- Depth limits set by the antenna you chose
Procedure matters as much as physics. Interpretation requires skill, and good practice includes reviewing drawings, a reconnaissance sweep, and cross-polarized or angled scans. Fast scans without that verification can miss hazards such as plastic conduits. Operators also run static calibration tests so they know how the equipment behaves in your particular slab.
When uncertainty remains, ask for a confirmatory step: targeted coring, scanning from both sides of the member, or a combined approach using more than one method.
Pro Tip: If a scan was done quickly on a wet or newly poured slab, ask for a re-scan once the concrete has dried and settled, and request an angled pass over any suspect area.
When should you scan, and how does it fit into pre-drill planning and your SWMS?
Schedule the scan early enough that its findings can shape the plan. Pre-drill planning should include a SWMS developed in consultation with workers and health and safety representatives, with steps such as scanning drill areas for electric cables, barricading, anchor fixation, water and slurry control, and marking drill centres. In practice, the sequence looks like this:
- Review available as-built drawings and walk the site, noting likely targets and obstructions.
- Set the scan area and grid spacing based on where you need to penetrate.
- Avoid scanning right after curing, when moisture is high, and allow the slab to settle.
- Complete the scan, then allow time for data interpretation and marking.
- Arrange any confirmatory coring before cutting or drilling begins.
- Prepare or update the SWMS, set exclusion zones, and confirm RCDs and equipment safety tags are current.
- Brief spotters and agree procedures for occupied spaces.
If people live or work nearby, preconstruction safety steps are worth reading for protecting an occupied space during noisy, dusty work.
How do you read a scan report and its “clear to” language?
A report is only as useful as your understanding of its claims. Phrases such as “clear to first rebar” or “scan clear to full depth” describe how far the operator can vouch for the slab, and that depends on the equipment and the penetration actually achieved. Ask what proof sits behind the statement.
Good mark-out practice follows SIM guidance, which calls for marking each target with at least three points:
- Use continuation arrows so the direction of each target is clear.
- Photograph the mark-outs for the job file.
- Confirm the markings match the written report.
Know when to push back. Ask for more if scan penetration is unproven, if dense rebar may mask deeper targets, or if nonmetallic conduits are suspected. The answer may be an additional scan, an angled scan, or a confirmatory core. For how coring is done once the area is cleared, see our guide to core drilling techniques.
What should a pre-drill checklist look like after the scan?
Turn the findings into action with a short, ordered routine:
- Review the scan report and attach it to the job file.
- Mark all targets using SIM guidance, which calls for at least three points per item.
- Update the SWMS and brief the crew on the findings.
- Set the exclusion zone and post signage, such as workshop safety signs.
- Secure anchors and confirm RCDs are in place.
- Confirm water and slurry control and the core removal plan.
- Photograph the mark-outs and keep every record.
Special cases need a specialist call or a different location: dense rebar grids, young or wet slabs, and suspected nonmetallic conduits. Keep the documentation for compliance and for future work on the same slab. Our concrete drilling safety tips cover the drilling stage in more detail.
Why do experience and licensed crews matter?
Scanning is valuable, but a scan alone does not make a hole safe. Interpretation and integration with the SWMS decide whether the information protects anyone. In our view, licensed operators, practiced calibration routines, and one team carrying work from scan to drill remove most of the surprises that blow out budgets. Handoffs between separate contractors are where findings get lost. If you want one accountable contractor, we offer scanning and drilling together, with documented safety processes.
— MYBMC
Book scanning and drilling with one licensed contractor
When you want the scan, the report, and the drilling handled by one team, we can do all three. We provide concrete scanning and carry out drilling and coring through our concrete drilling and core drilling services.
Your next step can be any of these:
- Request a quote for scanning plus drilling.
- Schedule a site reconnaissance visit.
- Ask for a technical consult on a tricky slab.
The scan supports safe execution on site. Start with a quote at Vic Sawing & Drilling and tell us what you plan to penetrate.
FAQ
Will concrete crack if I drill into it?
A properly sized hole drilled with the right bit rarely cracks sound concrete. Cracking is more likely near edges, over voids, or when the bit hits rebar or a duct. Scanning first helps you avoid those weak spots.
How much does a GPR survey cost?
Cost depends on the area, access, and depth required, and no price is published for our scanning service, so contact us for a quote. Being clear about what you need to penetrate helps us scope it accurately.
How can you tell if concrete has rebar or not?
You cannot tell reliably by looking at the surface. A scan locates reinforcement and shows its spacing and cover. Ferroscan and GPR are the usual tools, and drawings help but may not match what was built.
Is 2 inches thick enough for concrete?
Two inches suits some light toppings and overlays but can be too thin for structural slabs or deeper anchors. A scan measures actual slab thickness so you can pick a hole depth that stays inside it.
Sources
- Concrete Using Ground Penetrating
- Reliability and limitations of GPR for identifying objects embedded in concrete – Experience from the lab
- Safe concrete cutting and drilling
- Concrete Specifications – Subsurface Investigation Methodology
- GPR Concrete Scanning Australia | Concrete Radar | Forensic Engineering Group
