At a glance
The short version
- Tell us the cut, not just the room: where, how big, how deep, and why.
- Clear and clean the surface. Radar needs contact along every scan line — stock, furniture and floor coverings have to move first.
- Say the words "post-tension" if there is any chance the slab is one.
- The markup shows where the data supports a target and where it's inconclusive. Both matter.
- Marks are relative to the surface they're drawn on. Grind the floor or paint it, and the record is the photographs, not the paint.
_A concrete scan is most useful before the drill is on site and least useful after the first core is wet. Here is what to have ready, how to read the markup, and what the marks do and don't say._
What we need from you before the visit
The cut. A scan is planned around a penetration: a 4-inch core for plumbing, a saw slot for a trench drain, anchor holes for a rack row. The size, depth and location of the planned cut set the scan grid and how far around it we look. "Scan the room" produces a slower visit and a vaguer answer than "we're coring here, here and here."
The slab, as far as you know it. Age, thickness if known, elevated deck or slab-on-grade, and any drawings — structural sheets are gold even when they're wrong, because the difference between drawn and found is itself a finding. If the building could plausibly have a post-tensioned slab, say so when you book; it changes how the visit is planned, and how to tell is its own guide.
Access and conditions. Scanning requires physical contact along each pass. 1Jump to source 1 That means the surface cleared of stock and furniture, floor coverings lifted where the cut is, ceilings below an elevated deck accessible if we need to look from underneath, and a lift or ladder arranged for wall and overhead work. Our concrete antenna is compact enough for walls, ceilings and tight clearances 4Jump to source 4 — but somebody still has to be able to reach the spot.
Curing and moisture. Fresh concrete and wet slabs read poorly — moisture attenuates the signal and can mask targets. 2Jump to source 2 If the slab was recently poured, recently flooded or freshly cleaned with a lot of water, tell us; sometimes the right answer is scanning a few days later.
What happens on site
We scan a grid over and around each planned penetration, in two directions, and mark what the data supports directly on the surface: reinforcing steel, conduit, post-tension tendons, embedded pipe, and slab thickness where the bottom reflection is readable. Nondestructive methods for concrete — radar among them — are covered in ACI 228.2R, which is also candid about each method's limitations; that document is the professional frame for everything a scan can and cannot say. 3Jump to source 3
The markup uses a simple convention, explained on site and recorded in the photographs: target lines, inconclusive zones, and the proposed penetration relocated a few inches where relocating buys clear data. That conversation — can the core move six inches and land in a quiet spot — is where a scan earns its fee.
How to read the marks
- A marked line means the data supports a target there. It does not identify the material with certainty — steel, conduit and PT strand can present similarly — though pattern, spacing and depth usually make the identification confident, and we say when it isn't.
- An inconclusive zone means the data could not support a clean answer: congested steel, shallow interference, surface condition. It is not "clear" and must never be treated as such. 2Jump to source 23Jump to source 3
- Depth callouts are estimates. Radar depth in concrete rides on an assumed velocity, and velocity varies with mix and moisture. 2Jump to source 2 Treat depths as planning numbers, not clearances — the reasoning is the same as the depth error budget.
- Coverage is stated. The record says what was scanned and what wasn't. A target outside the scanned area was never in scope, which is why the marks around a core are not a statement about the rest of the floor.
What the scan cannot do
The working range of a high-frequency concrete antenna is real but finite — our system's specified range in concrete tops out around 75 cm under good conditions 4Jump to source 4, and a dense top mat of reinforcement can shadow what sits beneath it. 2Jump to source 25Jump to source 5 Radar interprets; it does not expose. No scan certifies an area, and any provider who says otherwise is selling something the physics doesn't offer. Where a penetration is critical — a tendon anchor zone, a suspect area, a structural member — the honest plan pairs the scan with small verification: a test drill stopped short, a chip-out, or a look from the underside.
After the visit
Photograph the marks before any work starts — paint on a working floor has a short life — and keep the job documentation with the project file. If the work scope moves, the scan doesn't move with it: marks apply to the scanned area on the scan date, and a new core location three feet away is a new question.
View 5 numbered sources
Sources
Every numbered claim above traces to one of these. Links go to the publisher of record.
- Utility Locating: Electromagnetic Locating — GPRS — https://www.gp-radar.com/manuals/utility-locating-electromagnetic-locating Referenced for surface-contact scanning practice common to contact methods.
- ASTM D6432-19 — Standard Guide for Using the Surface Ground Penetrating Radar Method for Subsurface Investigation — ASTM International — https://www.astm.org/Standards/D6432.htm Source for moisture attenuation, velocity-dependent depth and interpretive limits.
- ACI 228.2R-13 — Report on Nondestructive Test Methods for Evaluation of Concrete in Structures — American Concrete Institute — https://www.concrete.org/store/productdetail.aspx?ItemID=228213
- NX25 concrete antenna — GSSI Geophysical Survey Systems — https://www.geophysical.com/products/nx25 Source for the ~75 cm depth range and compact form factor for walls, ceilings and tight spaces.
- Ground Penetrating Radar for Concrete Evaluation Studies — Foundation Performance Association — https://foundationperformance.org/pastpresentations/gehrig_paper_march2004.pdf Source for practical penetration limits and congestion shadowing in concrete.
Sourcing and limitations
This guide is original writing by High Desert Scan & Locate, LLC. It cites third-party statutes, standards, codes and publications, all of which remain the property of their respective owners. We describe them in our own words and do not reproduce their text. Standards published by bodies such as ASTM, ACI, ASCE/UESI/CI and PTI are available from those publishers; where one governs your work, obtain the current edition and read it. The published source controls; our paraphrase does not, and an edition cited here may since have been revised or superseded.
No representation or warranty. This material is provided "as is." We make no representation or warranty, express or implied, as to its accuracy, completeness, reliability or currency. It is accurate only as of the review date shown, if at all. Laws, rules and standards change, and we do not undertake to update it.
Not professional advice. Nothing here is legal, engineering, surveying or safety advice, and reading it creates no professional or client relationship. It is not a substitute for a site-specific scope, and it does not clear any area for excavation, cutting or coring.
Company names, product names and trademarks are used for identification only and do not indicate affiliation, sponsorship or endorsement. We receive no compensation for any mention.
Corrections: info@highdesertscan.com. See our Editorial policy, sourcing and attribution.
Private utility locating supplements, and does not replace, public one-call (811) notification. Utility designation is Quality Level B per ASCE/UESI/CI 38-22 unless otherwise stated. GPR interprets subsurface conditions; it does not expose them. Results are interpretations of conditions present within the requested area on the service date, and depend on target material, depth and site conditions.
