Detecting embedded metal in masonry

Metal elements within masonry are utilised for either, creating a frame of a building eg. beams and columns or for tying or fixing different construction materials together eg. cramps, dowels or pins. Overall, the metal elements are used for increasing construction durability and strength.

The problem of corrosion of those metal elements is prevalent in heritage buildings built with corrodible metals, specifically those constructed before 1970s.

Knowing that advanced corrosion can cause visible deterioration of masonry walls and weakening structural integrity of the construction, acting preventatively by maintaining building enclosure will reduce the rate of the corrosion would be the most economical option.

Ground Penetrating Radar (GPR) survey will detect embedded metals and provide information about their exact location and depth. When necessary, information about wall thickness, structural details and other features eg. voids might be obtainable.  

Metal detectors, in theory, just like GPR can detect ferrous and non-ferrous metals*. In real life however, metal detectors struggle with detecting non-ferrous metals and alloys in which iron is only one of the components such as stainless steel.

Ground Penetrating Radar (GPR) has this advantage over the metal detector, that it can easily detect ferrous and non-ferrous metals, even if the metal element is relatively small in comparison to the rest of the structure.

In our survey to detect metal fixings and structural elements, we rely on both technologies GPR and metal locators.

*Ferrous comes from Latin name of iron- ferrum. Ferrous metals are those which contain iron, whereas non-ferrous metals do no.

Since iron is one of the most abundant elements in nature, so are iron-based ferrous metals. Non-ferrous metals or alloys include copper, aluminium, lead, tin and zinc. 

The survey for detecting embedded metal starts with scanning the surface with metal detector instrument to have a general understanding of the location of the embedded metal elements.

The next stage is scanning the surface with Ground Penetrating Radar (GPR) typically in a series of regularly spaced, parallel horizontal and vertical scans, however this approach can be modified depending on the shape of scanned surface and accessibility.

The deliverables are either:

- on site markings where all the findings are mark out with temporary survey pain, coloured adhesive tape, chalk or

-office based post-processing where the results are overlayed on the elevation drawing.

The comprehensive report is produced on client’s request.