During the last century many homes mainly in parts of Cornwall, Devon and parts of Derbyshire were constructed from concrete blocks. The manufacturers of these blocks used the waste materials/aggregates from the mines. Unfortunately it is now known that some of these aggregates contain small pieces of iron pyrite which is known by the Cornish name being ‘Mundic’.
When incorporated into concrete these minerals have proved to be unstable and through a complex chemical and mechanical process can ultimately lead to the complete breakdown of the concrete. In an advanced state of deterioration Mundic concrete becomes physically unsound and in severe cases has lead to a need to demolish the affected buildings.
Identifying a property that maybe affected by Mundic will usually require concrete screening testing. This consists of taking samples where the experienced surveyor feels appropriate. The samples taken will be 50mm (2″) diameter cores drilled to a depth of about 75mm to 100mm, which will be carefully recorded, labelled and submitted to a laboratory for examination. Before leaving the property all visible holes caused by the concrete sampling procedure will be repaired.
These are examined in a laboratory and determine the category as below:-
- Class A - Sound concrete satisfactory condition.
- Class A/B - Concrete considered sound subject to adequate protection and maintenance.
- Class B - Concrete contains more than 30% possible problem aggregates although appearing sound could cause potential problems.
- Class C - Those are found to be clearly unsound from examination