A slab that’s thinner than its design specification isn’t necessarily a visible problem, until it’s asked to carry more than it was built for. Whether that’s a warehouse floor being reassessed for heavier racking, a bridge deck approaching the end of its design life, or a road surface being considered for resurfacing, knowing the actual thickness of a slab, not the thickness it was designed to be, is often the deciding factor in what happens next.

Concrete doesn’t always end up exactly as specified. Formwork can shift during a pour, screed layers can vary in depth across a floor, and decades of wear, resurfacing or previous repairs can leave a slab thinner in places than its original drawings suggest. On older structures particularly, as-built records are often missing or unreliable, meaning the only way to know a slab’s true thickness is to measure it directly, without breaking into it to do so.

Our surveyors scan the slab, screed or deck using Ground Penetrating Radar, recording the radar signal as it reflects off each layer boundary within the structure. Because different materials reflect the signal differently, we can identify the transition between layers, concrete, screed, sub-base or void, and calculate thickness at each scanned point. Surveying on a regular grid rather than a handful of spot checks means we can show variation across a slab, not just a single average figure that might hide a thin section elsewhere on site.

Thickness data is used differently depending on the project. For a warehouse or industrial floor, it informs whether the slab can safely support new racking, plant or vehicle loading. For roads and car parks, it helps decide between resurfacing and full reconstruction. For bridge decks and other critical structures, thickness loss over time can be an early indicator of deterioration that needs further structural assessment. In each case, the same underlying question applies: does the slab, as it actually is today, still meet the demands being placed on it?

You’ll receive a report and CAD drawing showing measured thickness across the surveyed area, highlighting any zones that fall outside expected tolerance. This gives structural engineers a factual basis for assessing load capacity or planning remedial work, rather than relying on original design drawings that may no longer reflect the slab as it exists on site today. Where thinning is found alongside signs of internal deterioration, our Void Detection Using GPR service can investigate further, confirming whether voiding is a contributing factor to the reduced thickness identified.

Get in touch to discuss a slab thickness survey for your site, or call 0333 920 942.