Historically, the United Kingdom has been filled with unique, beautiful building materials that have in turn led to unique and beautiful building traditions.

Until the rise of easy ways to order consistent building materials through comprehensive wholesalers and later the internet, architectural traditions were entirely based around what was available at the time in the area.

Some traditions, such as the Longridge sandstone regularly used in buildings around Central Lancashire, are an adored part of the cultural and architectural tradition of the town and still endure to this day.

Other materials such as bungaroosh are more controversial and can vary wildly in complexity, quality and longevity based on the materials used and the skilful use of techniques to mitigate bungaroosh’s obvious structural deficits.

One construction tradition in particular from the late 19th century until the 1960s has become so controversial that every old house in a particular region of the South West of England is tested, which can make a home effectively unsellable.

This is the story of the mundic block problem.


What is Mundic?

Mundic is a word that originates from Cornish that describes a particular type of iron pyrite that was a byproduct of mining copper ore, although the definition has since expanded to include a couple of other materials such as reactive silica, clinker and Cornish killas, a type of fine grain rock.

All of these materials were used as aggregates in the production of concrete blocks, as they were a type of recycled waste that at the time produced an appropriately effective result made from recycled waste, typically from nearby mines.

The problem, it turned out, was that these materials, when affected by moisture, could start to degrade the concrete over time, with the consequent risk of significant structural damage due to the concrete material deteriorating, expanding and forming weaknesses and cracks.

They were commonly used in Cornwall and the area around Tavistock, as well as some other areas around Devon, although according to advice by the Royal Institute of Chartered Surveyors, this is significantly rarer.

Mundic blocks were used regularly until the 1950s, and by the 1960s mass-production methods had almost completely halted their use.

However, it took until 1985 for the issue to be understood enough for it to start being investigated. Mundic deterioration often has no telltale signs, meaning that a building could theoretically look fine until a major structural element collapses, taking some or all of the building down with it.

By 1992, the mechanic was better understood and the definition expanded beyond sulphates and metal oxides to any aggregate material that similarly deteriorates.

Because of this, any building with elements that trace back to before the 1960s in Cornwall and the Tavistock area are tested and classified, with certain types of failure making a home impossible to mortgage due to the uncertainty of lenders.

A building with mundic is not guaranteed to fall apart; it is often only found in small localised areas and removing the element with mundic and getting it retested will give it a clean bill of health.

Some investors took advantage of this by purchasing mundic-afflicted buildings for bargain prices and either removing the affected elements or leasing the property to rent, which the mundic would not affect.

Regardless, the mundic block problem is a fascinating example of the effects different local building traditions can have in the long term.