Independent Chartered Surveyors:

Sulphate attack on concrete floor slabs

Solid ground floor slabs can suffer from sulphate attack.  This is a serious problem because the floor slabs sometimes expand causing structural damage to the main loadbearing walls of a building. Sulphate attack occurs when the contents of the hardcore fill material that has been used beneath the floor slab contains Sulphate and there is enough moisture in the fill to cause them to attack the concrete floor slab causing heave. Hardcore containing sulphates is now prohibited from use beneath ground floor slabs. If you have a floor which is lumpy and bumpy and suspect sulphate attack it is necessary to make small holes in the floor, extract samples of the hardcore and concrete and subject tham to laboratory tests. To test for the presence of sulfates this will require breaking through the slab and a number of samples of the fill material and concrete be taken for laboratory analysis.  If suphates are found and the the floors are too badly damaged to be acceptable the only solution is to replace the damaged floors with modern ones. (Replacing the suphate fill at the same time.) The description of a suphate attack is described in my book

Domestic Building Surveys Domestic Building Surveys (The Builder's Bookshelf) (ISBN: 9780419178002)

Andrew Williams

Andrew R Williams & Associates

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Liverpool 0150 426 9660

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