Q. We have a quote from a Dutch company (Schrijver) using a ceramic porous tube mechanism. Why is this not accepted by PGA for insurance backed guarantee?

Submitted by: BT
 

A. Ceramic 'porous pot' vent type methods for the control of rising damp have been around for very many years; in the 1920s this technique was marketed by British Knapen. A Building Research Station report of 1930 after conducting field and lab tests concluded - 'Results indicate that no useful increase in the rate of evaporation of moisture results from the use of these tubes'.

The following is an extract from Building Research Establishment's recent publication 'Understanding Dampness' (2004) under the heading 'Porous Tubes';

'It must be true of course, that increasing the evaporation rate from a wall by boring holes can only help reduce the level of rising damp. The function of the tubes is, however, not clear. It is claimed that the tubes draw moisture to them but, if so, they must also draw salts. It is difficult to see how any significant evaporation can take place. If the salts are hygroscopic, the tubes could perhaps feed moisture from the air into the surrounding masonry when external humidities are high. Also, for the tubes to draw moisture from the surrounding structure, they must be more finely pored than the surrounding material. In general terms, the more finely pored a material the less permeable it is and the lower the evaporation rate from it, unless the material is virtually saturated. In that case, evaporation would take place mainly from the surface and the nature of the material would be of little importance'.

We are not aware of any 'porous pot' tube type system that has ever achieved independent third party accreditation. Because of the recent advent of 'novel' rising damp control systems we have had to introduce certain product stipulations that are acceptable to us. After all if someone claimed one day that lemonade was a great material to treat rising damp who are we to dispute this? It is therefore a requirement of the PGA that materials used or the control of rising damp for which a guarantee is required, must have independent third party accreditation from a body such as the British Board of Agrément.

We hope that the above answer, despite being long winded, is of assistance To you when deciding which process to use.