If you're buying, selling or renovating an older property in Cornwall, you may hear the word "mundic". It refers to a type of concrete deterioration that is closely linked to Cornwall's mining history, and it can affect whether a home can be mortgaged and what work it needs. This guide explains what mundic is, how testing works, what the grades mean and what the options are if a property is affected.
What is mundic?
"Mundic" is an old Cornish word for iron pyrite. In the building world, it's used for concrete made with aggregate taken from mine waste. Before the 1950s, mine waste was a cheap and plentiful source of stone and sand in Cornwall and parts of West Devon, and it was used to make concrete blocks and mass concrete for houses.
Some of that waste contained minerals, particularly sulphides such as pyrite, that react over time when exposed to moisture and air. The reaction can cause the concrete to expand, crack and lose strength. Not all concrete made with mine waste is affected, which is why testing is needed rather than assuming a problem.
Which homes might be affected?
Mundic is mainly a concern for properties built with concrete, or with concrete blocks, before around 1950 in Cornwall and parts of Devon. That can include:
Inter-war houses and bungalows built with concrete blocks.
Older homes that have been extended or repaired using concrete blocks.
Properties with mass concrete walls, foundations or garden walls.
Stone cottages and modern homes built with manufactured blocks are not usually a concern in themselves, but older extensions or repairs to them might be. Your surveyor will advise whether a test is recommended for a particular property.
How mundic testing works
Mundic testing follows guidance published by the Royal Institution of Chartered Surveyors (RICS). In broad terms:
A qualified surveyor inspects the property and decides whether testing is needed.
Small cores are drilled from the walls in several locations and sent to a laboratory.
The samples are examined to identify the aggregate and assess its condition.
In some cases further laboratory testing is carried out to see how the concrete is likely to behave over time.
Testing is usually requested by mortgage lenders when an older Cornish property is bought or remortgaged, but some owners commission it before planning a major renovation, so they know what they're working with.
Understanding the grades
The result is a classification of the concrete. In simple terms:
Class A means the concrete is considered sound. There are sub-classes, A1, A2 and A3, that reflect the type of aggregate and the level of risk. Class A3 concrete contains some potentially reactive material, and lenders may treat it differently.
Class B means the concrete is considered unsound or likely to deteriorate, and most lenders will not lend on a property classed as B without remedial work.
The exact wording and what each class means for a mortgage can vary, so it's important to read the report carefully and discuss it with your surveyor and lender.
What happens if a property is affected?
If a property is classed as B, the usual solution is to remove and replace the affected concrete. Depending on how much of the building is affected, this can mean:
Partial rebuilding, where specific walls, extensions or sections are taken down and rebuilt in new materials.
Full rebuilding, where the house is demolished and rebuilt, sometimes on the existing footprint. Our guide to replacement dwellings in Cornwall covers the planning side of this.
After remedial work, a property is typically re-inspected and, where appropriate, re-tested so that it can be reclassified. The work needs careful planning, a structural engineer's input and Building Regulations approval. Our project management and QS services can help with programming and budgeting.
Renovating a mundic-tested home
If your home has been tested and is classed as A, you can usually renovate and extend it in the normal way. A few sensible precautions help:
Keep a copy of the mundic report with your property documents.
Tell your designer, engineer and builder about the report at the start.
Avoid letting water get into older concrete walls by keeping gutters, downpipes, render and flashings in good repair.
Make sure any new extension is built in modern materials and properly tied in.
Our property renovations and home extensions pages show the type of work we take on, and our guide to bungalow renovation in Cornwall may help if you own an inter-war or post-war bungalow.
Mundic FAQs
Does every older Cornish home need a mundic test?
No. It depends on when and how the property was built, and on what your surveyor and lender require. Stone-built homes and modern homes often don't need one, but older concrete or block-built homes often do.
Can I get a mortgage on a Class A3 property?
Some lenders will lend on A3 properties and others won't, or may add conditions. It's best to speak to your lender or a mortgage broker who knows the Cornish market.
Can a Class B house be repaired rather than rebuilt?
Sometimes the affected parts can be removed and rebuilt while the rest stays. The right approach depends on the extent of the problem and should be decided with a structural engineer and surveyor.
Do you carry out mundic tests?
No. Testing is carried out by qualified surveyors and laboratories. We carry out the building work that follows, from partial rebuilds to full replacement homes.
Talk to us about your project
If you own or are buying a mundic-affected property, or simply want to renovate an older concrete-block home, call Cornish Building Company on 01208 816991 or contact us to talk through your options.
