Everything you ever wanted to know about pyrite, but were afraid to ask. KRYSTYNA RAWICZ gives us the details.

It is estimated that some 20,000 homes, principally in the North Dublin area, but also in Meath, Kildare and North Wicklow, are affected by the pyrite problem. In the longer term, it is possible that as many as 60,000 homes could be affected. Extensions constructed within the last 10 years could also be affected, as well as commercial buildings, car parks, roads and any other construction that may have been carried out using pyrite contaminated fill.

What is pyrite?
Pyrite (FES2 – iron sulphide) is a very common, naturally occurring mineral. Traces of it are naturally found in the sedimentary rock that is used to make crushed stone for backfill used in construction. If the amount of pyrite in the stone is below a certain proportion, no problems occur. However, if it is greater, problems can arise, as outlined in this article.

In the presence of moisture and oxygen, pyrite oxidises and produces sulphuric acid. The acid reacts with the calcium carbonates (for example limestone) found in the crushed stone.

This chemical reaction produces sulphate and can form gypsum, whose crystalisation will cause the stone to burst, the backfill to swell and the concrete itself to crumble and swell. This in turn puts pressure on concrete floors and foundations, and can result in structural damage to a property.

It is thought that improved construction practices of recent years, such as ensuring that hardcore is well consolidated before pouring concrete floor slabs, combined with the more rapid pace of construction in the years 2000 to 2007, have both conspired to exacerbate the structural problems arising from the presence of pyrite in hardfill.

Swelling of pyritic backfill is relatively complex and has scientific, technical and legal implications for developer, designer and building owner.

It is usually a slow process, and it can take ten years or more before damage starts to become apparent. However, swelling can begin to occur after as little as one year, if oxidation of pyrite has already started during construction.

The Irish story
In Ireland, the pyrite problem was first identified in 2007. The source seemed to be a single quarry (owned by the Irish Asphalt division of the Lagan Group, at Bayview, Ballycoolin), which had commenced operation in 2002. Since then, a number of other quarry sources have been identified. While the problem has been largely concentrated in Fingal and Meath, pyrite-related problems have also been recorded in counties Kildare, Wicklow, Dublin and elsewhere.

The Department of the Environment, Heritage and Local Government brought the matter to the attention of all building control authorities in mid 2007, and has since incorporated a new National Standards Authority of Ireland (NSAI) standard recommendation on the use of aggregates as infill for civil engineering and road construction work into the relevant technical guidance document of the Building Regulations. With new controls in place, the use of pyrite-contaminated fill is unlikely to occur in the future.

How to recognise pyrite damage
There are a number of typical problems/defects that arise as a result of pyrite used in the fill under a floor. None of these defects in isolation provide evidence of pyrite, but taken together they can point to pyrite being the problem. Typical defects include:

  • a ‘spiderweb’ pattern of cracking to a concrete floor, or star or cross shaped cracks that gradually spread;
  • floor ‘heave’ (bulging, rising);
  • needle-like white crystals visible near the cracks, which disintegrate when touched;
  • bulging or horizontal cracking of external walls at low level (below dpc);
  • cracking of internal partitions/walls – horizontal cracking at ceiling level, or vertical cracking above door openings;
  • more significant or major cracking to internal load-bearing walls resting on concrete over pyrite-bearing material;
  • bulging of internal walls;
  • internal doors sticking or jammed in an open or shut position; and,
  • kitchen worktops or other internal surfaces sloping.

Where pyrite damage is suspected, a Chartered Building Surveyor can carry out a more detailed investigation to assess whether the damage is, in fact, indicative of a pyrite problem. If pyrite damage is thought likely after the initial visual inspection, the next step is to arrange to have a core sample taken from under the floor for testing of the fill to confirm the analysis.

Repair of pyrite-damaged buildings
The repair process is disruptive and likely to be costly. The work essentially involves taking up the concrete ground floor of the property, removing all the fill from under the floor, replacing it with new fill, and reinstating the floor, complete with damp proof membranes, radon barriers, below ground services, etc.

This work will almost certainly require the property to be vacated, unless only a new extension is affected.

The work will need to be carefully specified and properly supervised, and should be carried out under the supervision of a suitably qualified professional, such as a Chartered Building Surveyor.

Likely cost of remedial works
It is not possible to assess the exact cost, as this will vary from house to house depending on the internal configuration, internal finishes, etc. However, it is estimated that at a minimum, the cost of repairing a single pyrite-affected house may be in the region of €20,000. This cost could be significantly higher if there are high cost finishes and fittings to be removed and replaced, or if any structural instability has occurred as a result of the damage to date.

Who pays?
Once the problem is confirmed to be pyrite, a solicitor should be consulted to review the various contracts, guarantees or warranties and insurances in place, and to establish whether legal action should be taken to recover costs for the work from a third party. To date the courts have generally found that liability rests with the quarry owner.

Homebond has taken the view that it is not legally obliged to provide compensation, and that liability for major defects only applies when the defect is the result of negligence on the part of a builder or his subcontractor. Following the recent court ruling, Homebond has said that the quarries are liable under the Liability for Defective Products Act 1991.

At present there is no Government grant available towards the work. In other countries, (e.g., Canada), governments have provided grant aid to homeowners to assist in undertaking the works.

The pyrite problem is significant, and very worrying for those householders affected. Surveyors will undoubtedly be involved in identifying and remedying damage to pyrite-affected houses, and in advising householders and other building owners on the more complex issues arising in relation to insurances and contractual liabilities. The technology and techniques of repair are not new, as similar problems have occurred both in Ireland and elsewhere, where inappropriate materials have been used for hardfill in construction.

KrystynaRawiczKrystyna Rawicz MA(Oxon) FSCSI FRICS
Krystyna is Managing Director at Krystyna Rawicz &
Associates and is a Fellow of the RICS and the
Society of Chartered Surveyors Ireland.