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Testing for Pyrite in Backfill

Property Health Check do not provide a testing service for pyrite, however based on a visual examination we will give you our opinion as to the likelihood of previous movement in the floors as a result of the presence of pyrite. Depending on the property, pyrite testing can cost in the region of €1,500 – €2,500.

If after testing (from a approved laboratory) you find that the back fill under your concrete floors is made up with contaminated pyrite rock, you will find as night follows day, that pyrite oxidation will occur under your floors which may lead to the lifting, swelling or heaving of the floor slabs and walls in your house.  The degree or extent of swelling will be determined primarily by the depth of back-fill under your floors and the percentage of pyrite in the back-fill.

In Ireland, the make up of the pyrite back-fill that results in the swelling is normally black in colour and to the naked eye looks like a type of mudstone or shale, not too dissimilar to crumbled bangor roof slates.

For those of us who think we don’t have any pyrite under our floors, it’s important to know that pyrite would be expected to be found in almost all quarries in Ireland. As a matter of interest pyrite occurs in most of the floors under our houses, but in such small percentages that it has no negative effect on our properties. Due to the abundance of pyrite, it is important to know the exact chemical make up of the pyrite back fill under our floors so that an accurate determination can be made as to future possible expansion if any, that may occur. This can only be determined by testing of the back-fill and measuring the full depth of the back-fill under the concrete floor.

To take a sample of the back-fill for analysis, a corehole would need to be drilled through the concrete floor so a sample of the gravel back-fill can be taken. Unfortunately in Ireland we find that it is very common for drilling contractors to take the top sample of back-fill directly under the concrete floor and use this sample for testing. While this sample would normally be sufficient to get an analysis of pyrite, it will not tell you about the depth of pyrite back-fill under the floor. Another common problem is for the pyrite testing contractor to take the easy root and drill through the floor in an easy to repair location. It makes no sense (besides taking shortcuts) for your contractor to drill in the hallway or under the stairs if the main concern is in the middle of the living-room or in the kitchen.

It is important when taking the sample that the full depth of the back-fill down to unbroken ground should be measured and the floor be properly repaired and sealed by an experienced building surveyor or engineer to ensure that the damp proofing membrane and radon barrier are maintained. You certainly don’t want your pyrite test to end up causing you a radon problem.

How to Test for Pyrite in the sample.

The sample of back-fill would be examined on site by the building surveyor.  A visual inspection will at best only give an indication of the likelihood of pyrite. The sample of the back-fill is sent to an approved pyrite testing company to be chemically tested. This pyrite test will conclusively show the pyrite levels present under the floors. The pyrite report in addition to the building surveyors inspection can determine if the back-fill is likely to expand in the future and by how much.