Mundic block problem
The Cornish word ''mundic'' is now used to describe a cause of deterioration in concrete due to the decomposition of mineral constituents within the aggregate. A typical source of such aggregates is metalliferous mine waste. RICS Professional guidance describes all of Cornwall and an area within 15 km of Tavistock as being areas where routine testing for mundic is required. The notes go on to state that testing should be confined to buildings which contain concrete elements (blocks or in situ) and that were built in or prior to 1950. However, the notes contain advice that testing may be required where there are visual or other signs of mundic decay. Testing leads to a classification of A (subdivided into A1, A2 and A3), B or C. All A classifications are sound, B is sound but contains sufficient deleterious aggregate for it to be considered unstable and C is unsound. Classifications B & C mean that a property may be unmortgageable. Typically a house is routinely screened if constructed between 1900 and 1960 from concrete block.https://www.cornwall.gov.uk/media/lqxe4xvt/mundic-block.pdfReferences
{{Portal, Cornwall