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Salts & Dampness in Buildings

Salts.

Dampness in Buildings may be apparent in a variety of forms, arising from a single factor, but often from several sources simultaneously. It is therefore paramount for a surveyor to correctly diagnose the cause or causes of the dampness in a property to then determine the correct remedial measures to eliminate the cause of the problem.

The Inspection.

The presence of dampness is often determined by the visual evidence available at the time together with the proper use of a moisture meter. We would always recommend that a dual facility electrical moisture meter is used preferably having both pad and pins, which if used correctly can ascertain the level of moisture and establish a pattern of the moisture distribution on a wall surface. However where a definitive conclusion of rising damp is required then further evidence can be gathered by measurement taken within the depth of the wall BS:6576 code of practice refers: This may then lead to further disruptive examination and involve the use of a calcium carbide “speedy meter” or even the removal of samples for laboratory testing using the gravimetric or oven drying process for determining accurate moisture content. However chemical testing can also prove valuable in assessing dampness and as such a SALT TESTING KIT can be used effectively.

Soluble Salts.

A number of salts may be present in the structure of a building. Ground water almost certainly contains dissolved mineral salts which tend to concentrate at the wall surfaces where water evaporates. The most common soluble salts associated with ground water are nitrates and chlorides and therefore, these can be used as natural trace elements by a competent surveyor.
Nitrates and Chlorides are hygroscopic salts and have the ability to absorb moisture from the atmosphere, thus potentially leaving a wall damp due to hygroscopic moisture alone. Plaster that is affected by moisture and hygroscopic salts should be removed and replaced with material which is able to withstand their effects-BS6576 refers: see also Heyen Re-plastering guide available on request.  Frequently white crystals or a dry white powder can be found on the surface of plaster or masonry. These are efflorescent salts, the most significant of which are sulphates. They are often present in masonry and their occurrence on the surface is indicative of the passage of water through a structure, possibly from rainwater penetration or as the result of the natural drying out process.

Sampling.

Sampling Procedure. Samples for testing can be wallpaper,plaster,render,mortar, or brick for example. Where the salts are visually obvious then there is usually no difficulty in deciding from where to take the sample. Where they are not so obvious, but there are signs of dampness then it is best to to take samples from the edge of damp since this is where evaporation will have taken place and the salts will have concentrated in those areas. We do not recommend that diagnosis is made based on a single sample, but results should be compared with a sample taken from an area clearly not affected by dampness which can be used as a control.

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