Mundic

View of the mundic works at Mount Morgan, circa 1905.

[edit] Introduction

Originally, the term mundic - a Cornish word - was used to describe a mineral (pyrite) that is found in rocks in Cornwall and Devon. Pyrite is a naturally occurring mineral of iron sulfide.

The term mundic has also been adopted to describe a condition that occurs when structures deteriorate due to the oxidisation of unstable sulphides (often including pyrite), sometimes incorporated into the materials that make up concrete. Concrete is the most commonly used man-made material on earth. It is a composite material, consisting mainly of cement, water and aggregate, which can include sand, gravel or crushed rock.

Aggregates are mixed with cement and water to provide bulk and to modify the physical and chemical properties of the mix. There are several desirable properties of aggregates:

• Clean: Free from any organic substances such as dust or other fine materials.
• Hard/strong: Most cement in construction is used to resist compressive forces.
• Durable: Must be able to resist forces over a long time period.
• Capable of good adhesion: The cement paste needs to physically bind to other aggregates and grip effectively.
• Good shape: Smooth and round aggregates provide good workability, whereas angular and rough aggregates tend to give better compressive strength.

One common source of aggregate is gravel or crushed rock from quarries. If that includes pyrite, the substance associated with mundic, the resulting material may produce sulphuric acid when exposed to moisture. The reaction, called sulphation, can have an impact on other materials in the concrete to form gypsum, which causes crystallisation and expansion. This can result in the deterioration of the concrete.

[edit] History

In the 18th and 19th centuries, Cornwall and Devon were widely mined for their rich natural resources - particularly copper and tin. As an inexpensive and plentiful substance, the mining waste material - high in pyric content - could be recycled and used in the aggregate mixture that was sometimes incorporated into concrete for construction in the early 20th century. From approximately 1900 to 1960, the practice of using this waste material in concrete for housing construction became fairly common.

Over the years, it became apparent that the integrity of concrete with pyric content could become compromised. When exposed to moisture, this material could actually erode the cement and cause the concrete to crack and make it vulnerable to even more moisture penetration, eventually causing it to crumble and fail in the most extreme instances.

[edit] Consequences of mundic

There are certain parts of the country where mundic-containing material has been used in some residential construction (particularly in the foundation of houses) in the form of mundic blocks. In these structures, it may be necessary to subject a property to testing before it can be sold. Unless the property passes the test, it may be difficult for the potential home buyer to secure a mortgage without going to a specialist broker.

A mundic test require that small samples of concrete are drilled out and sent to a laboratory for analysis. Test results usually take two weeks to arrange and complete.

For the purpose of obtaining a mortgage, the property survey results will be broken down into a report using these classifications:

Guidelines for mundic tests are provided by The Royal Institution of Chartered Surveyors (RICS).

Mundic block tests are typically conducted on residential properties in Cornwall or Devon using concrete (but not brick or stone) and built between 1900 and 1960; they will also be requested if decay caused by mundic is visibly apparent.

Reports can sometimes be transferred from one homeowner to another, but for mortgage purposes, the report must be made out in the name of the new homeowner. However, this is only possible if the original surveying firm is able to execute the transfer.

If a property receives a poor test result but the mundic block is limited to a specific part of the structure, it may be possible to replace those materials (or demolish that portion of the structure) for the property to be deemed suitable for sale. This may happen, for example, in situations where an older property (pre-1900, for instance) has had an extension added - using concrete - during a time when mundic materials might have been used. If only the extension fails the test and can be removed or rebuilt, it may be possible to secure a mortgage once the problem has been resolved.

[edit] Related articles on Designing Buildings

• Aggregate.
• Concrete.
• Deleterious materials in construction.
• Home ownership.
• Portland cement.
• Pyrite and mica redress issues in Dail Eireann.
• Radon.
• Royal Institution of Chartered Surveyors RICS.
• Tin.
• Types of cement.
• Types of concrete.

[edit] External resources

• The Royal Institution of Chartered Surveyors (RICS), The mundic problem (3rd edition).