Pyritic heave

Pyritic heave is a structural defect that occurs when pyrite, a naturally occurring sulphide mineral present in hardcore fill beneath concrete floors, oxidises upon exposure to moisture and air. This oxidation process transforms pyrite into gypsum, a mineral with a much larger volume. As the gypsum expands, it exerts pressure on the overlying concrete slab, causing it to lift and crack, while also distorting and damaging internal walls, finishes, doors, and windows. The issue most commonly affects houses with ground-supported concrete floors built on pyrite-rich fill, particularly from quarries or mudstone deposits, and typically manifests years after construction.

The signs of pyritic heave become visible gradually, often a decade after building completion. Common indicators include spiderweb-like cracking patterns on concrete slabs, uneven or humped floors, and cracks in partition walls or plasterboard. Doors and windows may begin to stick or fail to close properly due to structural distortion, while secondary damage appears in finishes like tiling and plaster. Because the process is progressive and driven by chemical reactions in the foundation material, early detection is crucial to mitigate costly structural repairs and protect building integrity.

Pyritic heave was a major problem in Ireland from 2006 to 2008, with thousands of properties found to, in particular around Dublin. These were said to be caused during the period of rapid construction that occurred during what was referred to as the Celtic Tiger economic boom, named in reference to similar 'tiger' booms that had occurred in Asia. During this time the use of reactive pyrite-containing aggregate on many projects left lasting issues. Other instances of pyritic heave have also been discovered in United States (Ohio and Pennsylvania), as well as Canada.

This issues were so signifiant in Ireland that a Pyrite Resolution Board (PRB) was established and the Pyrite Resolution Act of 2013 passed by the government. Following this a Pyrite Remediation Scheme (Scheme) was established by the government to remediate dwellings that had been significantly damaged as a result of pyritic heave caused by the swelling of hardcore under ground floor slabs. Under the Act the Pyrite Resolution Board was established, to oversee implementation of the scheme and manage the application and appeals process. In 2019 it was reported "Pyrite scheme extended as number of homes remediated reaches 2,000", the scheme continues today and is still run by the Housing Agency, who were prescribed under the Act, to carry out the remediation of properties accepted into the scheme.

For further information see "Pyrite Remediation Scheme. Guide for Scheme Participants" 3rd Edition February 2019.

[edit] Related articles

• Agglomeration.
• Aggregate.
• Alluvium.
• Archaeology.
• Cracking and building movement.
• Cracking in buildings BR 292
• Iron.
• English Heritage.
• Historic England.
• Latent defects
• Pyrite and mica redress issues in Dail Eireann.
• Soil survey.
• Types of soil.
• Why do buildings crack? (DG 361)