Why might you require one?
You may require this investigation and written report following an unfavourable mortgage valuation, Homebuyer Survey, building survey or property overview.
What does a Sulphate Report entail?
Clients must be aware that a sulphate report is intrusive. It entails breaking one or more holes through the ground floor slab and digging down to determine the characteristics of the floor slab including thickness and type of sub floor fill. A sample may then be taken for laboratory analysis. The hole is reinstated with concrete upon completion of the investigation.
Hough & Co provide recommendations and also monitor the excavation process providing a fully detailed specification in accordance with current Building Regulations. A report is also compiled upon successful completion of the replacement floor which is acceptable by financial institutions and mortgage lenders.
Why is sulphate a problem?
A hardcore containing sulphate is now banned from use below floor slabs, and in any case there is now a requirement for a damp proof membrane which would prevent sulphate attack. Typically the problem houses are those built by local authorities in the 1950's and 60's in mining areas. This is because colliery shale, which contain sulphates, was used for hardcore.
Sulphate attack on ground floor slabs is a very serious problem which can cause structural damage to the main walls of a building. These sulphates migrate into the concrete which reacts with the concrete causing it to expand. This results in heave of the slab and structural damage to the external walls as the slab pushes them out.
For sulphates to affect the slab there must be moisture present. Migration of the sulphates is prevented if a damp-proof membrane is present between the fill and slab. There may be no sulphate attack if an effective damp-proof membrane is in place. However, moisture contents can vary and increase to very high levels if an undetected water leak occurs. Also damp-proof membranes can deteriorate with time. Whenever sulphates are present there is a potential problem for the future.