Ferro Scanning

Ferro scanning tells you where the steel is in a concrete slab, wall or column before anyone drills, cores or cuts into it. Our surveyors scan the area with a ferroscan cover meter, mark each bar on the surface along with its depth, and show your team where it’s clear to drill, so fixings and cores go between the bars rather than through them.

You may also hear it called a ferroscan, rebar scan or cover meter survey. The jobs range from a single set of anchor bolts to dozens of cores for a new plant room, and we carry them out for Tier 1 contractors, M&E installers, developers and homeowners. Subvision Surveys has more than 3 decades of surveying experience and is Essex-based, working nationwide.

A ferroscan sends a low-power electromagnetic field into the concrete. Steel disturbs that field, and the instrument works out where each bar is and how much concrete covers it. Nothing is drilled or broken out, and the area can be used again as soon as we’ve finished.

We scan in two directions so both layers of the top mat show up, and switch to a gridded image scan where you need to see the full bar pattern rather than a handful of lines. Each bar is marked on the surface with its depth written alongside, and where you’ve told us your drilling positions we mark which ones are clear and where to move the rest.

A cover meter is at its most accurate in the outer layer of steel. As a rule it reads reliably to somewhere between 150 and 180 mm of cover, and accuracy falls where bars are bunched tightly together or lapped.

A ferroscan only sees metal, and only near the surface. It won’t find plastic conduits or voids, it can’t measure how thick a slab is, and it can miss a second mat of steel sitting deep in a thick section.

Post-tensioned slabs are the biggest concern. Cutting a live tendon is dangerous and expensive to put right, and tendons often sit deeper than a cover meter reads. On PT slabs, thicker sections, or anywhere conduits and voids matter, we add handheld concrete GPR. It reads several hundred millimetres into the slab and picks up non-metallic features as well as steel. Our pages on locating post-tensioned tendons, GPR concrete slab surveys and slab thickness measurement explain those surveys in more detail.

If you’re not sure which you need, tell us how the building was constructed and what you’re planning to do, and we’ll tell you before we price it.

Ferro scanning isn’t only done before drilling. Measuring cover depth tells engineers whether there’s enough concrete protecting the steel. Low cover is one of the most common reasons reinforcement corrodes and concrete spalls, particularly in car parks, balconies, coastal structures and anywhere de-icing salts are used.

The guidance for this work is BS 1881-204, which covers the use of electromagnetic cover meters. We take cover readings across the areas your engineer specifies and report them against the bar layout, so they can be compared directly with the design cover. For a fuller picture of a structure’s condition, cover surveys can be combined with rebound hammer testing and ultrasonic testing on the same visit.

• Bars marked on the surface with their depth, so the information is there for the drilling team the moment we’ve finished
• Clear zones and approved drilling positions marked where you’ve given us your setting-out
• A survey drawing and report showing bar position, spacing, orientation and cover depth for each area scanned
• GPR plots for any areas surveyed with concrete GPR, showing tendons, conduits or voids
• Notes on any areas we couldn’t scan, such as fixed equipment or metal floor finishes, so nothing is assumed clear when it wasn’t checked

Where you need the full reinforcement layout of a slab or structure rather than clearance for specific positions, our rebar mapping survey is the better fit.

• Cores and fixings for M&E services, sprinklers and drainage during fit-out
• New openings in slabs and walls for stairs, lifts and risers
• Fixing balustrades, cladding brackets, racking and machinery bases
• Ground-mounted EV chargers and barriers in multi-storey car parks
• Checking existing structures before refurbishment or change of use
• Investigating reinforcement before demolition or partial removal

We carry out ferro scanning across the UK, with dedicated pages for Kent, Hertfordshire and Sussex.

One call covers ferro scanning, concrete GPR, rebound hammer and ultrasonic testing, so you don’t need a separate specialist for each part of a concrete investigation. We’re SSIP and ISO accredited, hold SafeContractor, CHAS and Constructionline certification, and price at competitive rates whether the job is one drilling position or a whole building.

Call us on 0333 920 9427 or use the form. It helps to send drawings or photos of the area, what you’re planning to do (drilling, coring or cutting, and to what depth), and when the area is accessible. If the scan has to happen outside working hours, let us know when you book.