Detecting embedded metal in masonry
GPR, supported by a metal detector, finds cramps, dowels, ties and structural steel hidden in masonry. Remedial work can then be targeted at the right places without opening up whole walls.
What the survey finds
When you need this survey
Metal has been built into masonry for centuries. Stone facades are held with cramps and dowels, cavity walls with ties, and many early twentieth-century buildings have steel frames encased in brick or stone. When water gets into the wall, this metal corrodes. Rusting steel expands, which causes staining, cracking and displacement of the masonry. In the worst cases, sections of facade or the structure itself can fail.
A survey is used:
- to investigate cracking, staining or displaced stonework
- to plan repairs on historic and listed buildings
- to locate the frame in steel-framed masonry buildings
- before cutting or drilling into masonry
- to inform a condition survey of a facade
What the survey finds
GPR detects both ferrous and non-ferrous metals, so it finds copper and bronze fixings as well as iron and steel. It locates fixings, ties, beams and columns within the wall. It also shows wall thickness, voids and other internal features. A metal detector confirms metallic targets close to the surface.
How it is done
We scan the wall surface in lines or a grid, from the ground, a scaffold or an access platform. Findings can be marked on the wall. The data is processed in the office and the positions of the metal are plotted on elevations in CAD, with a report that sets out the findings and where further inspection is recommended.
Limits you should know about
Very thick or rubble-filled walls reduce the detail GPR can show at depth. Small fixings deep in the wall are harder to detect. GPR shows where metal is, but it cannot measure how badly it has corroded. Opening up at a few selected points confirms the condition. Access to upper levels may need scaffold or a platform, which we can discuss when quoting.
Why use GPR
- No damage to historic fabric.
- Finds metal that a metal detector alone may miss.
- Allows targeted, local repairs instead of wholesale opening up.
- Shows wall construction at the same time.
We have carried out these surveys for local councils and heritage clients.
Questions we're asked
Can GPR tell how corroded the metal is?
No. GPR locates the metal and can show related cracking or voids. A small opening-up at selected points is needed to check its condition.
Will the survey damage the stonework?
No. The antenna is moved across the surface and nothing is drilled or removed.