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Does rainfall affect the rate of Pyrite expansion.

Is the total amount of rain fall in Ireland speeding up the rate of pyrite expansion under our houses from what is happening in Canada.

There is a mis-conception in the building industry and by some building professionals that the rate of pyrite expansion of contaminated backfill should show up more quickly or become evident in Ireland, then is the case in Canada.  The argument put forward to substantiate this view is that because Ireland is a much wetter country then Canada that the moisture levels in the backfill will be higher and therefore expand more quickly. This view does not hold any water for the following reasons.

The rate of expansion in the contaminated pyrite backfill under a concrete floor slab is subject to three main ingredients,

  • Percentage of pyrite in backfill.
  • Moisture content in backfill.
  • Air-oxygen to allow for chemical reaction to take place.

For expansion to occur in the pyrite backfill you need all three ingredients to come together.  If any one of the above ingredients is not present, then expansion of the backfill under the concrete floor will not take place.
The pyrite damage to houses in Ireland is mostly confined to the greater Dublin region. The total rainfall shown in the Dublin Airport station is significantly less then the total rainfall shown in the other stations around the country. When you compare the rainfall from the Dublin Airport station (see figures below) it is about 50% less then the rainfall that falls in the Montreal region of Canada. We all accept that it seems to rain more often then not in Ireland, but when the rainfall statistics are taken into account the total amount of rainfall in Montreal, Canada is higher then in the Dublin region. The rainfall in Montreal is also spread out over the entire year, not too different to what happens in Ireland. Therefore the argument that pyrite expansion in Ireland would be expected to show up quicker then Montreal because of our wetter climate is not founded on fact.

There are other site conditions that have to be taken into account in addition to the total amount of rainfall when considering the likely increased rate of pyrite expansion due to moisture.

These conditions include,

  • the location of any particular site (is it in a very flat area or dip which leads to poor water drainage,
  • what is the height of the water table in the area, particularly during rainy periods,
  • the type of soil under the contaminated backfill, does the type of soil naturally contain higher moisture levels,
  • is there cracks in the rising walls or floors allowing moisture to enter more quickly into the backfill,
  • what is the drainage or gradient like immediately around the property,
  • are there small leaks in the waste plumbing pipes under the house, in most cases small drip leaks may not be noticed in most houses, but with houses with contaminated back fill, these leaks act as a serious catalyst to expansion,
Central Statistics Office Ireland

Weather Summary Total Rainfall (mm)

Station 1962 1980 1990 2000 2003 2004 2005 2006
Kerry
1,232.3
1,775.5
1,334.8
1,786.2
1,508.0
1,398.9
1,500.1 1,760.7
Cork Airport
1,042.2
1,303.8
1,032.7
1,147.3
967.7
1,115.4
1,191.7 1,198.3
Dublin Airport
654.2
825.1
728.4
840.2
653.3
702.6
683.1
740.0
Kilkenny
790.5
898.1
842.1
936.9
742.7
803.3
757.9
895.2
Malin Head
991.3
1,084.3
1,310.8
1,175.9
842.3
1,141.3
1,086.1
1,156.9
Mullingar
968.2
1,007.6
1,022.1
1,008.1
737.7
953.1
866.7
1,004.5
Shannon Airport
921.2
1,043.1
1,023.9
1,100.3
773.3
903.7
914.2
968.5
Source: Meteorological Service

Source, Central Statistics Office, Skehard Road, Cork, Ireland.

 

Rainfall in Montreal, Canada

Source, Montreal, Canada, Weatherstats
Date           Sum Current Year
1986           1,033.90 mm
1987           900.90 mm
1990           1,111.60 mm
2000           985.80 mm
2001           768.90 mm
2002           811.70 mm
2003           1,121.90 mm
2004           899.40 mm
2005           1,231.70 mm
2006           1,343.10 mm
2007           999.60 mm
2008           1,111.60 mm
2009           974.60 mm
2010           1,194.00 mm
2011           1,084.20 mm