Case study. December 2014


We took instructions from an owner/occupier wishing to sell a Grade II listed property in the centre of Taunton.

We were instructed to carry out tests on the ground floor walls because a prospective purchaser had previously invited a contractor to carry out a damp inspection on the ground floor walls before the purchase commenced. The contractor’s report stated that rising damp was detected using a conductivity meter (damp meter). The contractor suggested that the rising damp was due to the absence of a physical damp proof course and had therefore recommended the removal of the internal plaster to at least 1.2M high, followed by a chemical injected damp proof course and the subsequent re-plastering with hard sand cement render.

As Independent Specialist Surveyors, we have a variety of tools at our disposal to identify dampness in properties. One such tool is the Speedy Carbide Test (SCT). The SCT is an item of apparatus used by specialist surveyors to determine the moisture content within the walls and is an accurate diagnosis of dampness or otherwise within the property.

The SCT has a greater degree of accuracy which includes taking a sample of masonry, as compared to the Protimeter Moister Meter (conductivity meter) which will only give an indication of moisture on the surface of the walls and could be confused with condensation. The apparatus itself contains a sealed vessel that is thoroughly cleaned before each test is carried out. This prevents any discrepancies with the result that it provides an accurate reading. We drilled a number of holes in the ground floor walls with a slow percussion masonry drill to get samples to test the moisture content. The samples were weighed using accurate scales and poured into the flask standing vertically. Once the sample was placed carefully within the flask, calcium carbide was measured and placed into the lid of the flask, ensuring the two substances did not mix. The lid was then securely placed on the flask, still being held vertically and then shaken vigorously to mix the substance together. By mixing the sample with the calcium carbide, any moisture within the sample reacts with the calcium carbide and releases an acetylene gas. This gas builds up within the flask turning the dial at the bottom of the flask, allowing the surveyor to calculate the percentage of moisture within the sample. If the total moisture content reading is above 4% in traditional brickwork within the walls, it would suggest that the moisture content is higher than that which could be regarded as dry. It must be stressed that these figures are dependent on the porosity of the brick substrate. In this case, the reading was very much lower than 4% and it was our recommendation that remedial works suggested by the contractor were not necessary. We were told that this had saved the client many thousands of pounds during the final negotiation.