The best concrete scanning service for a Sydney CBD job is the one that turns up with both ground penetrating radar (GPR) and electromagnetic (EM) equipment, can work inside a live building with limited access and tight noise windows, marks out directly on the slab in a way your driller can follow, and gives you a…
What makes a concrete scanning service the "best" in Sydney CBD?
The best concrete scanning service for a Sydney CBD job is the one that turns up with both ground penetrating radar (GPR) and electromagnetic (EM) equipment, can work inside a live building with limited access and tight noise windows, marks out directly on the slab in a way your driller can follow, and gives you a written record of what was found and what could not be seen. On a CBD site, availability and access experience matter almost as much as the gear. A scanner who has never worked a basement carpark with a 2.1 metre height limit, a loading dock booking and a building manager who wants the job done between 6pm and 10pm will cost you a day.
Here is how to judge one before you book.
What concrete scanning actually finds (and what it does not)
Scanning a slab, wall or column before you core, drill, saw cut or chase is about finding three things: structural reinforcement, embedded services, and voids or slab edges.
- Reinforcement — rebar mats, mesh, shear studs, and in suspended slabs, post tension cables. Cutting a PT cable is the expensive one. It can fail explosively and it can compromise the slab.
- Embedded services — conduits, water and hydraulic lines, data, and anything a previous fitout buried.
- Slab detail — thickness, cover, permanent formwork such as Bondek, and voids.
What scanning does not do is guarantee an empty hole. A GPR antenna has a practical depth limit in concrete, heavy congested top mats can mask what sits beneath them, and wet or freshly poured slabs scatter the signal. An honest operator will tell you where their confidence drops and will suggest a slightly moved core location rather than pretend the whole slab is clear.
GPR, EM and what the difference means for your job
Most CBD scans use both. They answer different questions.
| Method | What it detects well | Limits | Typical use in the CBD |
|---|---|---|---|
| Ground penetrating radar (GPR) | Rebar, mesh, PT ducts, conduits (metallic or plastic), voids, slab thickness from one side | Depth limited in dense or wet concrete; congested top steel can shadow lower targets | Core holes, saw cuts, anchor points, slab thickness checks |
| Electromagnetic (EM) locating | Live or traceable metallic services, cables that can be energised or signal traced | Only finds conductive targets; needs a connection or an induced signal | Confirming live power and comms in walls and around the slab edge |
| Combined GPR and EM | Cross checks one result against the other | Takes longer, costs more per point | Anything near switchboards, risers or unknown fitout history |
If a provider only offers one method, ask what they do when the two results would disagree. On CBD fitouts with layers of past tenancies, that cross check is usually what stops a mistake.
What affects the price
No one can quote you a real figure without knowing the site. These are the things that move it, and you can use them to compare quotes fairly:
- Number and spread of scan locations. Twenty core points in one room costs far less per point than five points across four levels.
- Access and timing. After hours, weekend, night work, induction requirements, permit to work and hot work paperwork, loading dock bookings and lift access all add time.
- Mobilisation. Sydney CBD parking and travel is real cost. Sites around Parramatta and Western Sydney often price differently to the CBD for this reason alone.
- Deliverable. Marks on the slab only is cheaper than marks plus photos, a scan report and a CAD or PDF overlay.
- Concrete type. Post tensioned slabs take longer and need more care than a ground bearing slab.
- Standby time. If your driller is waiting on the scanner, or the scanner is waiting on a building manager to unlock a room, someone pays for that hour.
A quote that is far cheaper than the others is usually pricing fewer points, a shorter window, or no written record.
Signs of good work, and signs of bad
Good work looks like: clear crayon or paint marks on the slab showing rebar lines and conduit runs, not just a vague box; a marked safe zone with dimensions; depths written next to the marks; photos of every location before drilling; a note of where the operator was not confident; and someone who will stay while the first core goes in if the location is risky.
Bad work looks like: a single X on the floor with no context; no mention of slab thickness; no photos; "it's all clear" over an entire level; refusing to put anything in writing; and an operator who cannot tell you what antenna frequency they used or why.
One practical test: ask what they would do if they found congested steel right where you need the core. A good answer offers alternatives (shift the point, reduce the hole, scan from the underside, core in stages). A poor answer is "she'll be right."
Questions to ask before you book
- Do you bring both GPR and EM, and will you use both here?
- Can you scan from one side only, or do you need access below the slab?
- What do I get afterwards: marks, photos, a report, a drawing overlay?
- Have you worked in occupied CBD buildings with after hours access and permit systems?
- What is your call out and minimum charge, and what happens if the site is not ready when you arrive?
- Are you insured, and can you provide a current certificate of currency?
- If the slab is post tensioned, how do you handle it?
Before you drill: the wider picture
Concrete scanning is one piece. If you are coring through a ground floor slab, breaking out for a pit, or trenching outside the building line, you also need to know what sits in the ground below and beside the slab. That is a subsurface utility investigation job: EM and GPR across the ground, then careful vacuum excavation to physically prove the depth and position of anything critical before plant goes near it.
For works in and around the public road reserve and near live assets, the standard reference point is the Before You Dig Australia enquiry, plus the asset owner's own requirements. Plans from those enquiries are a starting point only. They are not survey accurate and they do not show anything a previous fitout buried.
Where LCG Locators fits
LCG Locators is one option for this work in Sydney. We carry both GPR and EM equipment, scan slabs, walls and columns ahead of coring, cutting and anchoring, and back the marks up with reporting you can hand to a builder, council or principal contractor. We also do utility locating, survey and mapping, and non destructive vacuum excavation across the Sydney metro area and wider NSW, so a slab scan and the ground services around it can be handled in the one visit.
FAQ
Can you scan a slab if I can only get to the top side?
Yes. GPR works from one face and is the usual method for suspended slabs where the underside is above a tenancy or is covered by a ceiling. Access to both faces improves confidence, especially for slab thickness, but it is not required.
Does a fresh slab need to cure before scanning?
Green concrete holds a lot of moisture and that degrades radar results. Older slabs generally scan better. If you must scan early, expect reduced depth of view and say so to the operator up front so they can plan the scan and note it in the report.
Who is responsible if something gets hit after a scan?
That depends on your contract, but practically it comes down to whether the drill went where the marks said. Photos of the marked locations before drilling protect everyone, which is why a scan with no written record is a false economy.