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Site diagnosis for dampness - the correct approach

When a dampness problem develops there frequently follows a period of concern as to the origin of the situation. Sometime the answers are very obvious, other times they are not. Indeed, in some cases it may lead to a dispute or litigation. In the latter case it is essential to determine if there is a real problem, what is its origin and, of course, who is responsible. There is absolutely no point in taking legal action if there is no case. Thus, all assessments must be objective to advise the client of the problem - whether it is their problem or someone else's!

In order to obtain a proper objective diagnosis, laboratory and analytical services are frequently required as part of the investigation. It is essential that such services are undertaken fully and objectively. The wrong, or more likely, insufficient proper data, can lead to an unnecessary dispute and the associated expenses.


On site damp investigations require several essential evaluations:


  •  Assessment of risk of condensation (very important during the colder months), and also the general moisture production verses ventilation (differential vapour pressures).

  • Where rising or penetrating damp is suspected full moisture/salt profiles will be needed. This involves taking several vertical series of samples of masonry (5 - 8 samples per series) to evaluate total, free and air dry (hygroscopic) moisture contents of the materials.
  • Where there is also a question of replastering then an analysis of the new render is sometimes required: this should be undertaken in accordance with the British Standard and based on a minimum of calcium and silica content to determine the composition of the mix. A British Standard sand grading may be required if the sand was distinctly specified as part of the mix.
  • Should sulphate attack of cement based materials be suspected perhaps due to gypsum being added to a mix, then a proper sulphate determination may also be required. It is essential that sulphate content is related to cement content - one needs to know the proportion of 'combined sulphate' in the mix. Again, there are British Standard methods for analysis.
  • Use of our eyes, and common sense!

It is quite clear that where proper evaluations are undertaken it may become expensive, but it is essential to understand that if data is not full* or assessed by authoritative methods then the objectivity of the investigation may be compromised or worse still - wrong!

* (However, beware of 'excess' analyses - this holds true for any type of investigation, damp, timber, etc. - at best the results may only prove interesting but add nothing to the object of the investigation, and at worse they may be totally irrelevant and expensive! Analyses and data should only be obtained where they will be of direct relevance.)


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