Non Destructive Testing (NTD) involves the use of scientific techniques to assess the current state of a building, civic engineering structure such as a bridge, canal, aqueduct, or work of sculpture. Lots of old buildings have been reclaimed renovated and turned into housing, office buildings or to serve some other functional purpose. People who fancy a life in the countryside buy a 300 year old derelict barn or other farm building to convert into their dream home. In addition, historically important churches, castles and stately homes and Listed Buildings are always in need of renovation.

Anyone intent on renovating any type of structure needs to be able to determine its current state. Old techniques for doing this involved taking material away for laboratory analysis, which was more often than not detrimental in itself. NDT enables in situ testing without the need to remove anything from the site, irrespective of whether the structure was build of wood, stone, concrete or brick. It can satisfy the requirement of the renovator to understand, in depth, the sort of task being taken on.

A primary consideration might be to use NDT to discover the order in which building took place. The original architectural drawings, if they ever existed, are unlikely to be available and understanding how thick walls and other internal structures are, and where brick header and stone boundary courses, voids and hidden spaces created by extensions and bolt-ons added to the original building overtime are located are likely to be crucial to the project. NDT can look at the stress a structure is under, where beams or joists are carrying too much load. It can also determine where concrete has been used and whether it has been reinforced with Stainless Steel Beams and rods. NDT will help to provide the answer to important questions, such as whether the building can be saved. If so, what will need to be achieved and what the cost will be. NDT can take into account the state of all materials used, the effects of time on those factors and an assessment of all types of detrimental effects such as weather, seismic activity and climate.

NDT assessments are made using different techniques depending on the material being tested. Often this is accomplished using probes. The main methods used include:

• Sound – ultra-sonic
• Penetrating radiation
• Visible light; and
• Electromagnetism.

The strength of concrete can be tested using a rebound hammer which fires a specified energy at the test site. The rebound strength is captured and indicates how hard the concrete is. This is crucial in helping to determine how healthy the concrete is. It is also possible to check what the water content of the concrete is and whether it has suffered salt contamination. In addition to concrete NDT can be used to assess masonry damage and grout solidarity. It can also report on damage to gargoyles and drainage features and crenulation on ancient churches.

At national heritage sites all over the world NDT is being used along with other techniques to preserve crumbling edifices and restore important sites top as far as possible, their original state. A very famous example of this is the 20m work done over a decade on the twelfth century bell tower of Pisa Cathedral, known as the Leaning Tower of Pisa, to stop it collapsing. The tower was straightened, not completely, but by 18 inches, enough to protect it for a couple more hundred years.