Pyrite, or fools gold, is a naturally occurring mineral which is can be found in quartz beds associated with quarries. From a geographic perspective, some regions of Ireland have a higher concentration of pyrite than others.
When Iron Pyrites exposed to the atmospheric oxygen and water it reacts to create a sulphuric acid. If combined with calcium carbonates such as Limestone, which is present in aggregate, it can expand. In extreme cases – in mines for examples – it has been also know to spontaneously combust!
In a building context, the problems start where there are higher levels of pyrite present ( >1%) in the gravel mix provided by quarries to developers. Builders often use this gravel mix as hardcore infill – which is the aggregate mix that is used to level off and fill around the foundations of your home when it is being built. This infill is boxed off by the rising wall structure around your foundations and is then covered with a ground bearing slab. So now any pyrite from the gravel is very much a part of your buildings structure – and if it starts expanding it ‘shift’s the infill and can put continuous pressure on the ground bearing slabs and walls of your house, causing them to strain buckle and eventually crack.
At this stage it is important to note that in most cases the cracks, bulges and imperfections on display in your house are most likely not down to pyrites. In a newer house most are down to normally occurring – although not acceptable - settlement cracks caused by the drying our of plasterboard, warping wooden floors etc. The good news is that these are more easily and cost effectively remedied. More serious causes outside of pyrite damage include structural issues such sinking foundations due to ground subsidence. These all need to be addressed but it is important to realise that there is more than one cause for structural aberrations in your home. Please click here to see article on settlement cracks for more details.
That said there are some tell tale signs relating to the structural issues caused by pyrite that you can look out for – as follows:
Concrete floors raising or cracking in a ‘spider web’ type pattern - Internal doors not shutting due to raise in floor levels.
Load bearing walls below the damp proof coarse bulging outwards.
Load bearing walls showing large structural cracks from floor to ceiling
What to do if I suspect Pyrite damage?
Get a structural engineer or building surveyor in to do a site investigation. They will be able to rule out pyrite where not applicable. If it is suspected you will need to get a sample of the infill by drilling through the ground bearing slab and take a sample for lab testing. As little as 1% pyrite can cause structural problems in the right environment!
How do I fix it?
It’s not pretty. Remedial works will require replacing the infill from under the ground bearing slab in a home. This means evacuating the hose of all fittings and lifting the ground bearing slab. The house will be uninhabitable for a prolonged period.
It’s open to debate at the moment. A combination of the developer / builder, the quarry (if legal action is pursed) and Homebond (if applicable) is most likely.