Pyrite Heave, What It Is and Which Properties Are at Risk

What is Pyrite Heave?

Pyrite heave is a form of structural floor heave caused by the oxidation of iron sulphide minerals, primarily pyrite (FeS₂), contained in hardcore fill material used beneath concrete ground floors. When pyrite-bearing hardcore becomes wet, a chemical reaction produces sulphuric acid, iron compounds, and expansive secondary minerals (particularly gypsum and jarosite). The resulting volume increase causes the concrete floor slab to lift, sometimes dramatically, cracking walls, jamming doors, fracturing drainage, and rendering properties uninhabitable in severe cases.

The condition is irreversible without full excavation and replacement of the affected hardcore fill. Remediation is costly and disruptive, typically requiring the removal of all ground floor finishes, the concrete slab, and the fill material beneath it, followed by replacement with certified inert aggregate.

Where is Pyrite Heave a Problem?

Pyrite heave is primarily associated with the Republic of Ireland, where a specific source of crushed aggregate, pyrite-rich greywacke from a quarry in County Wicklow, was used extensively in housing built between approximately 1997 and 2006. The Irish government established the Pyrite Resolution Board to manage remediation of affected properties.

**In Great Britain, the risk is much lower but not zero.** Isolated incidents have been identified in:

• Parts of Scotland, particularly where local quarried aggregates with elevated sulphide content were used
• Occasional individual cases in England, linked to the use of colliery spoil, blast furnace slag, or other secondary aggregates as hardcore fill

The Property Care Association (PCA) and the Building Research Establishment (BRE) have both published guidance noting that the problem is geographically concentrated and that properties in England and Wales built using standard certified aggregates face minimal risk. That said, any property with unexplained floor heave, cracking above door frames, or visible floor distortion should be investigated.

How Surveyors Assess for Pyrite Risk

A RICS Level 3 Building Survey (formerly a Full Structural Survey) is the appropriate starting point. A surveyor will note visible symptoms of floor heave and may recommend specialist investigation. Key indicators include:

• Upward bowing of the ground floor slab, particularly in the centre of rooms
• Diagonal cracking at window and door openings (particularly at corners)
• Doors sticking or gaps between door frames and the floor
• Cracking or displacement of wall/floor junctions
• Damp or discolouration at floor level

Where pyrite is suspected, a specialist report should be commissioned from a PCA-accredited contractor or a geotechnical engineer. Investigation typically involves:

1. Core sampling through the floor slab to retrieve hardcore material

2. Laboratory analysis for total sulphate content and sulphide content

3. Assessment against BRE Special Digest 1 threshold limits

Buying a Property Where Pyrite is Suspected

If a survey flags possible pyrite heave, instruct a specialist before exchanging contracts. Mortgage lenders will frequently decline to lend on properties with confirmed pyrite heave until full remediation has been carried out and certified by an approved contractor. Retention of purchase funds until remediation is complete is common practice.

Property Passport UK records building survey data and condition flags against individual properties. Where a pyrite investigation report has been uploaded by a previous owner or professional, that document forms part of the property's permanent passport record, saving future buyers from commissioning duplicate investigations.

Key Organisations

• **Property Care Association (PCA)**, publishes guidance on sulphate attack and trains specialist contractors
• **Building Research Establishment (BRE)**, BRE Special Digest 1 sets the technical thresholds for sulphate-bearing fills
• **RICS**, Level 3 Building Survey standard covers assessment of floor condition and suspected structural movement