26 Mar Are damp-meters a waste of time?
Anyone with problems of dampness and who has researched on the internet may discover posts highly critical of the use of damp-meters which are a standard piece of Surveyors equipment used also by the many damp-proofing ‘Specialists’. Those who have had a Survey carried out in their own house or flat may have noticed the Surveyor prodding the walls with the ubiquitous yellow device, on hands and knees getting into all the chimney breast recesses and hopefully taking care not to spoil decorations.
So are we wasting our time? The simple answer is probably not.
The question which needs to be asked is however how is the Surveyor interpreting the results and what are the recommendations which follow. Is the wall fabric damp or is it just superfical dampness affecting the surface of the wall and plaster finishes.
If dampness is discovered and this results in a recommendation for a Damp and Timber Report to be carried out by a ‘Specialist’ then the most common outcome is a quote for injecting the walls to try to create in impermeable barrier and for re-plastering the walls with a modern plaster with water-proofing additives which will remain superficially dry for a period of time. This is not good if the cause of the dampness is not addressed.
It is always essential to look for the roof causes of dampness. We recently surveyed a property which had serious dampness from ground level to the ceilings at first floor level. No doubt recommendations had been made to install a damp-proof course (although there was a perfectly good damp-proof course in the walls) and to renew the plaster inside but did the ‘Specialists’ check the roof which had very old and leaking coverings and did they consider the fact that the wall affected was a solid wall, with old render finishes directly exposed to the prevailing weather? There are almost always factors which need to be addressed other than installing a new damp-proof course. Indeed injecting old (rubble) stone walls will be ineffective and a new plaster finish counter productive if it traps dampness in the walls.
Old houses will function well without a damp-proof course if the building is well maintained using traditional materials and techniques such as lime mortar, lime plaster and lime render. The use of cement products and even a cement lime mix for mortar and render must be avoided in all old properties where the walls need to breathe. Cement render and modern plaster is acceptable for modern properties which have very different construction techniques. You do need to be prepared to tolerate a certain amount of dampness in an old property.
The damp-meter is essential in identifying the moisture content of various elements (damp-meters are calibrated for timber) when carrying out a Survey but it is the recommendations which follow which must be subject to scrutiny.
Damp-meters are also essential when checking for penetrating water, for example beneath chimneys and parapet walls, where the dampness may not be detectable by sight or smell.
We shall be continuing to use the damp-meter when undertaking Surveys but it will remain rare that we refer you to a commercial contractor whose main purpose is to install injection damp-proof courses. It is the Surveyors role to provide the independent and impartial advice.
We do have a list of contractors who are specialists in working with older houses and may be best placed to advice and provide quotations. One of the leading companies in this field is Ty-Mawr who are based near Brecon. They specialise in natural and sustainable products and have systems suited for insulating old walls, designed to minimise the risks of dampness and having accreditations from the LABC (Local Authority Building Control).