Cover meter survey

What the survey finds

When you need a cover survey

Concrete cover protects reinforcement from corrosion and fire. Too little cover and the steel rusts sooner, spalls the concrete and loses strength in a fire. A cover survey is commonly needed for:

• condition assessments of car parks, bridges and frames
• fire risk assessments of concrete structures
• structural checks and load capacity calculations
• checking new work against the specified cover
• avoiding rebar strikes before drilling or fixing

What the survey finds

The survey gives the depth of cover to the reinforcement and the position and spacing of the bars. Results can be marked on the surface, or presented as a drawing with depths, contours or a colour map showing where cover is low.

GPR or cover meter?

We use both, depending on the job.

A cover meter uses electromagnetic induction to detect metal near the surface. It is simple and well suited to spot readings on small elements.

GPR covers large areas quickly and collects more information in the same pass. As well as cover, it shows deeper layers of reinforcement, conduits, voids and, in many cases, the element thickness. It also detects non-metallic reinforcement, which a cover meter cannot.

On many jobs we use GPR for coverage and a cover meter to check specific locations.

Accuracy and limits

Both methods need calibration to give reliable depths. We calibrate against a known depth, such as an exposed bar, a core or an edge, where one is available. Closely spaced bars, laps and congested areas affect cover meter readings. Dense reinforcement can hide deeper layers from GPR. The report states the method used and any limits for your structure.

Why a non-destructive cover survey

• No breaking out, so no repairs afterwards.
• Large areas measured with little disruption.
• Much cheaper than an intrusive investigation over the same area.
• Clear drawings that engineers can use directly.

Questions we're asked