Before 1950 in mid and west Cornwall and up until 1965 in parts of south Cornwall some concrete blocks were made with mine waste.
The mining industry in Cornwall goes back over 1,000 years reaching its peek in the 19th century. The problem with Mundic concrete is caused by the use of mine waste aggregate used to make the concrete.
The rock that is mined to extract tin and copper contains a host of minerals. Cassiterite is the mineral from which tin is extracted so once the Cassiterite has been isolated the rest of the material was dumped. The geological conditions under which Cassiterite is formed results in the creation of many other minerals, one in particular is iron pyrites which is often referred to a ‘Fools Gold’. The old Cornish word for ‘Fools Gold’ is Mundic.
‘Fools Gold’ is a sulphide bearing mineral and when incorporated within concrete can over time react with water that can be present as dampness causing a chemical reaction which results in the cement binding the aggregate being altered to form Gypsum. This leads to an expansion of the concrete and failure of the cement binder so in effect the concrete crumbles.
The occurrence of properties affected by Mundic is closely but not exclusively linked to the areas where mining was most intensive such as the towns of Redruth and Camborne, and the coastal towns of St Agnes and Perranporth. Whilst the occurrence is less frequent in areas such as the Roseland and the Lizard peninsula there is still a risk that it could be present.
In 1994 the RICS published Guidance Notes on the testing and sampling of concrete in Cornwall and parts of Devon. Julian Crosby and Paul Davison have been supervising tests since the Guidelines were published and Julian has recently sat on the RICS Steering Committee and was closely involved in the drafting of the new guidance notes that came into effect in January 2016.
Since 1994, DowlingDodd have tested nearly 2,000 properties all over Cornwall from St Ives and Penzance in the West to Liskeard in the east and Port Isaac on the north coast for Mundic.
Even old stone buildings need to be considered where for example they have been extended and possibly Mundic blocks were used. In Camborne for instance we have come across terraced cottages that look like they a entirely built of stone but on further investigation the party walls have been found to be of concrete and some of these are made of Mundic.
When carrying out a survey we will advise you if a Concrete Test is needed. Whilst there can be tell-tale signs that a property is affected by Mundic such a cracking to walls there are many cases where we find the building appears sound and only after carrying out a Mundic Test have problems come to light.
We work closely with several partners when testing. Cornwall Consultants www.cornwallconsultants.co.uk are our main contractor that we use them for drilling and taking samples. Petrolab are our Petrographers and they analyse the samples to provide us with a classification.
Our Reports are accepted by all lenders including Santander who will only recognise surveyors on their approved list.
A property that is found to have unacceptable concrete is not mortgageable, the value and saleability is affected and the structure could potentially fail so it is absolutely essential that the proper checks are carried out before you buy.