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 Use of electrical moisture meters

When damp investigations are undertaken using electrical moisture meters, one frequently hears the comment that such meters don't measure dampness in walls or other masonry substrates and therefore they are misleading. As a result some authorities would argue that quantitative results should be obtained, but try persuading a vendor to allow you to remove samples from their newly decorated walls in the course of a general survey!

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Electrical moisture meters -v- carbide moisture meters

In the recent press there has been considerable 'sniping' against the use of electrical moisture meters for diagnosing dampness in masonry substrates. The snipers rightly point out that the meters do not measure dampness but show changes in electrical resistance, capacitance or radio wave reflection/absorption in the substrate, depending on the type of electrical moisture meter in use.

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Condensation - the basics

Condensation is the most common form of dampness in buildings. Indeed, it appears to be more of a problem in modern properties than our historic buildings due to the introduction of double glazing, draught exclusion which basically cut down the natural ventilation of the property. Older properties, say, with sash windows, open fire-places and gaps around the original doors and windows are far less likely to be severely affected by surface condensation..

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Equilibrium Relative Humidity (ERH) - the pitfalls.

With the advent of better moisture meters, more knowledge on dampness and affordable hygrometers, measuring moisture in buildings can become quite sophisticated.


Take condensation for example. Measurement of relative humidity, air temperature to determine the dew point temperature, and then determined the surface temperature in relation to the dew point will tell us, or at least give us an indication, as to whether surface condensation is occurring or the likely risk of it developing at a particular time. So the measurement of relative humidity is a very important - in some cases.

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How damp is damp?

One frequently gets requests to undertake an investigation for dampness following building surveyors reports usually prior to the sale of a house. Inevitably they have found dampness with the aid of an electrical moisture meter and requested further investigation.

On questioning the client over this reported dampness it often becomes evident that there is no visible or physical problem - decorations are in good order, no peeling or lifting of wallpaper, no staining, no eruption of plaster finish or paint film. Clearly no obvious problem. Yet it was reported damp.
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BRE Digest 245 'Rising damp in Walls: diagnosis and treatment' - A Guide or a Specification?

When evaluating dampness in buildings one of the most useful procedures is to investigate the distribution of moisture, that is the free and air dry moisture contents: the presence of free moisture indicates a source of water ingress.

The method of moisture analyses and removal of samples is given in Building Research Establishment Digest 245, 'Rising damp in walls: diagnosis and treatment'. The Digest describes the size of the drilled be used, the method of sampling and the regimes for drying and weighing in order to obtain the objective distribution of moisture. Whilst the method described in the Digest is basically for evaluating rising dampness, it is extremely useful for evaluating any source of dampness, especially 'salt damp', other than condensation.

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Evaluating the performance of chemical injection damp-proof courses.

rdampContrary to a vociferous minority view, rising dampness does occur and is not that uncommon in properties without physical damp-proof courses (just put a brick/mortar in water and watch it wick). Where rising dampness does occur and warrants remedial action then a chemical injection damp-proof course may be considered. Over the years there have been a number of problems of continued dampness following the insertion of a chemical injection damp-proof course. However, considerable argument can arise as to whether the problem is due to the damp-proof course, replastering or other factors: this tends to form the basis of related disputes.   

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Sampling for Moisture and Soluble Salt 'Profiles'

When investigating dampness it is very often essential to accurately evaluate the cause of that dampness. Where a definitive diagnosis is required, perhaps for litigation purposes, this will require sampling from which data can be obtained regarding the distribution of water within the material. It is this distribution of moisture which identifies whether there is an actual source of water ingress (free moisture) or whether the 'dampness' has some other cause ('salt damp' - hygroscopic moisture).

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 'Salt damp' - the problems

Electrical moisture meters will respond to very small quantities of free moisture and certain contaminant salts. In building materials the latter are usually hygroscopic, that is they have the ability to absorb moisture from the atmosphere. The more humid the atmosphere the greater the absorption of atmospheric moisture, and also the greater the concentration of salts the greater the absorption of moisture. Where such contamination exists alone (that is without the presence of free moisture) high electrical moisture meter readings will be obtained even though the surface may appear visually dry. However, where contamination is high, and should it get into decorative finishes there are occasions when a wall can look very damp solely as a result of moisture absorption from the air. Such dampness is regarded as 'salt damp'

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Five percent moisture in walls - is it dry?

"There's less than it 5% moisture content in the wall - the damp-proof course is working perfectly"

How many times have we heard this statement? The client has called someone back because they still have a damp problem. The 'Test' - usually involving a Carbide meter - shows less than 5% in the wall; this, the client is told, is 'acceptable' even though there may be spoiling due to dampness.

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 The facts about chemical damp-proof courses and replastering

There are a number of factors to be taken into account when considering chemical damp-proofing systems and attendant replastering works. The following guide is intended to provide an objective insight into chemical damp-proofing, its performance and the importance of the replastering works.

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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!

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How damp is damp?

One frequently gets requests to undertake an investigation for dampness following building surveyors reports usually prior to the sale of a house. Inevitably they have found dampness with the aid of an electrical moisture meter and requested further investigation.

On questioning the client over this reported dampness it often becomes evident that there is no visible or physical problem - decorations are in good order, no peeling or lifting of wallpaper, no staining, no eruption of plaster finish or paint film. Clearly no obvious problem. Yet it was reported damp.

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 'Non-destructive surveys' -- The expectations?

Almost all the surveys/inspections undertaken by specialist damp and timber companies involve 'non-destructive' evaluations; it is currently standard industry practice.

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BBC's 'Raising the Roof: January 1999'

Having posted a review of BBC's 'Raising the Roof' 2000, I thought it might be useful to show what variation was obtained in their 'Raising the Roof' relating to damp proofing shown in January 1999.

The basis of the programme was that dampness within a particular property in Birmingham was not attributed to rising dampness, but to anything but rising damp. The house was set up so that a number of specialist damp-proofing surveyors looked at the building and gave their opinion. Yes 9 out of the 10 diagnosed rising damp. The programme then went on to show they were wrong - but they weren't!!

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A cautionary tale!

Most initial the diagnoses of dampness are undertaken using an electrical moisture meter (qualitative method of moisture measurement) - and quite understandably so: they are quick, clean and non-destructive.

Perhaps, as a result, high readings and a suitable pattern of readings are obtained and rising damp is diagnosed following which a chemical injection damp-proof course is installed. Fine.

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A review and opinion of performance data relating to an environmentally controlled damp-proofing system

1. INTRODUCTION:

In recent years there has been some significant advertising in the national press about a Patented, damp proofing system developed in Europe. Advertisements claim that it will Schrij_diageffectively cure rising damp, condensation and penetrating damp. Similar claims are to be found on the Internet

 

 A European Patent was granted for the units. The Patent (EP 0 829 587 B1) describes the units in full and claims the units to be “Improved device to abstract moisture from a wall or similar, ----“: the patent then continues to describe the improvements.

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Assessing the internal environment and condensation

1. EQUIPMENT REQUIRED

  • Surface temperature thermometer (infra-red or direct contact)
  • Thermo-hygrometer
  • Psychrometric chart (included below)
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BBC's 'raising the roof'



Once again the BBC have produced one of their low budget, spy-on-the wall progarmmes, this time about the timber preservative industry, ie, those who actually treat timber.

Some of you may remember the last programme produced about a year ago (January 1999) where they 'investigated' the damp-proofing trade -- however, what they didn't show on that was the results of analytical work which conclusively showed there was active rising dampness in the building!! In fact the 3 consultants they used all gave different diagnoses, one reporting a flood, one reporting bridging of the dpc and the final one who produced the analytical work showing rising dampness saying nothing!

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The Truth about Rising Damp

Over the last few years there has been a considerable amount of 'debate' concerning the existence of rising damp. Indeed, there has even been a book written, "The Rising Damp Myth" in which the author claims exactly that - rising damp is a myth.

 

By definition a 'myth' is 1. Any fictitious story, or unscientific theory, belief, etc, and 2. Person or thing whose existence is fictional or unproven account,

 

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Distribution of Moisture and Soluble Salts in Masonry

Moisture

The total moisture within a material is the sum of the moisture due to moisture absorbed from the air and any wetting from some source of water, eg, rain penetration, rising damp.

Hygrosopic or Air Dry moisture content:

All materials composing the basic fabric of walls, eg, stone, brick, render, plaster, contain various amounts of moisture, the amount depending on the specific material and the moisture equilibrium of the surrounding environment. This standing level of moisture is known as the air dry or hygroscopic moisture content of the material.

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