GPR for floor slab condition surveys
A GPR floor condition survey goes beyond reinforcement mapping — it can identify delamination, voids, and deterioration without breaking out a single tile or screed. Here is what is involved.
Most concrete scanning is commissioned to clear a drilling position. A floor slab condition survey uses the same technology for a different purpose: to assess the state of an existing slab across an area, looking for the defects that explain why a floor is cracking, lifting, sounding hollow, or failing earlier than expected. This post explains what a GPR floor condition survey can and cannot tell you, and what the work involves.
What a condition survey is looking for
Reinforcement mapping answers the question “where is the steel?” A condition survey asks a broader one: “is this slab sound, and if not, where and why?” The features of interest include:
- Voids beneath the slab. Loss of support under a ground-bearing slab, often from washed-out or settled fill, leaves the concrete spanning unsupported.
- Delamination. Horizontal separation within the slab, common where a topping or screed has debonded from the base, or where corrosion has split the concrete at the reinforcement plane.
- Slab thickness variation. Slabs poured against uneven ground or to a loose tolerance vary in thickness, which matters for both load capacity and any planned cutting.
- Moisture and deterioration. Persistently damp or deteriorated concrete behaves differently to sound, dry concrete on a radar scan.
The value is that all of this is assessed without lifting the floor finish. A tiled, screeded, or coated floor can be surveyed in place, and breaking out is reserved for confirming specific findings rather than hunting for them blind.
How GPR reveals condition
GPR detects boundaries between materials with different electrical properties. A sound, continuous slab gives a clean, predictable return: a strong reflection from the base of the concrete and regular signatures from the reinforcement. Defects disturb that pattern.
A void below the slab changes the reflection at the slab base, because concrete-over-air reflects differently to concrete-over-soil, and the signal often shows a characteristic phase change. A delamination introduces an extra reflecting horizon partway through the slab where there should be continuous concrete. Areas of high moisture attenuate the signal — the radar energy is absorbed more quickly, so deeper reflections weaken or disappear, which itself flags a problem zone. The surveyor reads these departures from the expected pattern across the survey area and maps where the slab behaves abnormally.
A condition survey therefore works best as a comparative exercise. The surveyor establishes what a good area of the slab looks like and then identifies where the data deviates from it. This is why surveying a reasonable extent of floor, not just a few isolated lines, produces a far more reliable result.
Why area coverage matters
A condition survey is about extent as much as presence. Knowing that a floor has a void is of limited use; knowing the void runs along one wall for fifteen metres and stops short of a column line tells an engineer where to focus repair and how much of the floor is affected.
For larger floors — warehouses, retail units, car park decks, industrial slabs — collecting that coverage by hand is slow. This is where large-scale GPR systems are used: multi-channel arrays, often vehicle-towed or pushed in wide swathes, that survey a floor quickly and produce dense, gridded data across the whole area. The result is a continuous map of slab condition rather than a set of scattered traverses, and on a big floor it is the only practical way to get representative coverage.
What the survey delivers
A floor condition survey is normally delivered as plans of the surveyed area, marking the location and extent of voids, delamination, thickness variation, and zones of probable moisture or deterioration, with a written interpretation. Recommendations for confirmatory investigation — targeted cores or breakouts at the worst points — are usually included.
That last point matters. GPR identifies anomalies; it does not, on its own, prove their cause. An attenuated zone might be moisture, contamination, or a change in the concrete mix. A reflection partway through a slab might be a delamination or a deliberate construction joint between two pours. The proper use of a condition survey is to find and bound the problem areas efficiently, then confirm the cause with a small number of well-placed cores. Cores chosen from a GPR survey are far more useful than cores placed at random.
When to commission one
A floor condition survey earns its place when a floor is showing symptoms — cracking, hollow-sounding patches, lifting finishes, settlement — and the cause is not obvious; when a slab is about to take a new use or heavier loading and its current state is unknown; or when a floor is being assessed before refurbishment, sale, or change of ownership.
Used in the right place, a GPR floor condition survey turns an invisible, whole-floor question into a mapped, bounded one. It will not replace the engineer’s judgement or the confirmatory core, but it tells both where to look — and that is usually where most of the cost and uncertainty in a floor problem hides.