Not all damp surveys are the same

Sometimes only the best will do. You may choose to reward yourself for all your hard work over the years with that Ferrari you always coveted in your youth, or maybe a Rolex watch. At other times the best you can get is essential, like when buying a car safety seat for your baby.

Like everything else in life, damp surveys vary tremendously. It should therefore come as no surprise to hear that I have been called in countless times in the past for a second opinion, or to resolve damp problems that arose/reappeared following works carried out as recommended in other damp surveys. These damp surveys were produced by a wide range of companies and surveyors – national and local. As I often got to see the original report, I must by now be one of the leading experts on third party damp surveys!

To be meaningful, complete and useful, any damp survey must be almost the equivalent of what used to be called a full structural survey – I should know, I used to do full structural surveys and depending on the age of the house, 80-90% of every survey was devoted to checking for damp and the problems it causes. I'm not referring just to obvious damp patches on walls, mould in corners, or mushrooms growing from the skirting boards. Things like cracks in walls, failing wall ties, woodworm in floors and roofs, springy floors, or even subsidence, can all be the result of undiagnosed damp.

To ensure you get the very best advice on how to resolve any existing damp properly without doing lots of unnecessary work, and to detect the early stages of future damp problems so they can be averted, requires the very best diagnostic and detection equipment. Ongoing technological advances mean that new equipment is constantly becoming available – while much of this is often a cheaper new version of existing high quality equipment, occasionally something appears that can genuinely reveal more about your damp. This means diagnostic and detection equipment needs to be regularly reviewed so it can be enhanced when appropriate with replacement or supplementary equipment. The following equipment is typical of that currently used by me in the past for a damp survey:

  • It is vital to know the humidity and temperature conditions in different parts of the building. These are measured with a Vaisala HM42. These instruments are built to order in Finland and are the only meters with a probe fine enough and long enough to measure the conditions in hard to reach spaces, such as underneath wooden ground floors.
  • Hidden inconsistencies within the structure can make certain areas prone to damp or mould. These often create incredibly tiny temperature differences on the surface of walls and ceilings, which can be detected by thermal imaging cameras. These temperature differences are detected by a Testo 875-1i which is one of the most sensitive cameras available – it is twice as sensitive as most other cameras available for building diagnostics.
  • When checking for cool areas and insulation defects that could trigger mould growth or condensation, a Flir Bcam thermal imaging camera is used. The Flir camera is older than the Testo camera and not quite as sensitive, but it has a different range of capabilities, making the two complementary.
  • Due to the natural variability of moisture contents within different materials, and even within adjacent parts of the same material, the only guaranteed way to determine if a wall is damp is to measure the actual moisture content inside its timber components. This is done using an Orion 930. This is a specially designed American meter that can precisely measure the moisture content up to 19mm deep inside any timber. This series of meters, are the only ones that can measure this important deep moisture independently of the moisture content at the surface, and without causing any damage. For hard to reach areas, and smaller or awkward shaped timber, a complimentary meter is occasionally needed – in these cases a Protimeter Surveymaster with pin probes on an optional long lead is used.
  • To locate potential moisture and salt problems in and behind plaster, particularly dense modern plasters, variations in the electrical capacitance within the walls is measured using a Trotec T660 meter. To ensure penetration through modern plaster, this meter is capable of measuring the capacitance up to 4cm within the wall – around 2 times deeper than most other meters.
  • To locate and track moisture even when hidden deep inside walls, a Trotec T610 meter is used to send microwave pulses into the walls and measure the distinctive reflections returned by water molecules. This is currently the only meter able to do this, and it allows moisture to be detected when it is hidden up to 30cm inside the wall.

Using these specialist instruments together, enables walls to be mapped in the detail required to work out if you have an existing or developing damp problem. This data, together with any visual evidence recorded, must then be analysed and cross referenced to determine what the real problems are, where any damp is coming from, how advanced it is, what damage is occurring, and how to rectify it – this stage can easily take several days.

The following letter details one client's experiences as a result of sub-standard damp surveys.

A personal story of damp survey experiences

Dear David,

Further to my telephone call, again thank you very much for your letter.

As I said to you at the time of your survey, dampness in the plaster of the lower parts of ground floor walls, especially in the hall, had been present for very many years – but I had put off doing anything about it because overall it didn’t seem to be getting any worse, it was better when the central heating was used more, and I had been told that ‘treatment’ would involve extensive, high, stripping of plaster in association with Damp Proof Course (DPC) injection.

However, in 2012 a surveyor [from a large well known national damp proofing company] assured me that the plaster was all fine and that only DPC injection was needed, and I decided to go ahead, and had this done by them in a lot of the ground floor walls - getting their 30 year guarantee against ‘rising damp’.

Because this work did not resolve the problem, I complained to them in July and December 2013, and on the latter occasion they sampled the brickwork from the worst affected areas in the hall. The samples were chemically tested (in my presence) and found to be dry, so they rejected my complaint against them.

Then, still concerned, I reverted to a local company of experience, who in January 2014 ‘treated’ the ‘rising damp’ (as they said) in the hall walls by extremely intensive DPC injection and stripping of the plaster to a height of 1 metre. When they re-plastered the walls they left only a small gap between the bottom of the plaster and the floor, and they re-mounted the skirting boards at their original level. For these areas I got their 30 year guarantee.

This work certainly improved the hall situation (obviously, in retrospect, by changing the original plaster which had accumulated salts) – as did separate re-plastering of a kitchen and a cloakroom wall prior to re-decorating – but some recurrence of low level dampness in the plaster of the hall walls ultimately led to me asking you last year for your assessment and opinion.

Of course your report revealed the true diagnosis and made sense of the whole situation. As you said at the time you strongly doubted if the brickwork had ever been damp.

Just to record that in the period 2012 to 2014 I thoroughly checked all the skirting boards which were removed to allow DPC injection, and found only one small area (about a couple of inches) of (? old) woodworm damage/decay on the back of one board. I treated this area intensively, and painted the backs of the original skirting boards with (real) creosote, and where in the hall I replaced some boards because of surface damage accumulated over 80+ years and /or in the removal of them – painted the backs of the new lengths before they were fitted.

Since your report I have not proceeded to having the plaster removed to a height of 3 inches and the skirting boards raised (I noted that you did not feel this to be a matter of urgency) so there remains some low level dampness in the plaster. Currently I expect this to lessen when the central heating goes on in the winter. I would of course prefer it not to be there, but in the context of all that has gone before, and with the reassurance of your report, for the present I will just accept and monitor it.

I did have the kitchen chimney breast wall re-plastered as you advised, and it and the other walls which were done independently of DPC injection seem fine.

Your other recommendations concerned the outside of the property, and I’ve had :

  • A gap created between the front wall of the house and the low garden wall.
  • The timber in, actually 2, of the bay window bottom corner joints replaced, and all the front windows repainted (the side and back ones are UPVC).
  • The little splits in the rendering above the kitchen window and door repaired and repainted.
  • The ground around the side and required part of the front of the house lowered to expose two clear courses of brick work beneath the DPC.

This letter is just to let you know the outcome of your survey and report, and to record for anyone interested the whole situation.

Once again my sincere thanks for your expert advice and help.

Yours sincerely,

As a matter of interest, the letter above refers to chemical testing of the wall to prove it was dry. Fortunately in this case, the wall was dry but this method generally only ever seems to be used when a company has a vested interest in 'proving' that a wall is dry! What they don't tell you, is this test is incredibly easy to falsify. If not done correctly it will always give a low or zero moisture reading and even when it doesn't, the result is often meaningless anyway (I won't bore you with the technical reasons why). One thing you can be absolutely certain of though – if anyone does a chemical moisture test on your wall and it gives 0% as proof of a dry wall, the test has not been done correctly.

Currently, I still undertake a small number of damp surveys on listed and period houses – I no longer carry out surveys on any property built since 1940 and no longer carry out mould/condensation surveys. At present, I still offer a choice of 3 fixed price survey packages based on the time needed to survey varying amounts of dampness in houses of different sizes:

  Damp plus Standard damp Basic damp
Time allowed for survey inspection: Up to 5 days Up to 1 day Up to ½ day
Suitable for:
  • Widespread and severe dampness affecting a moderate or large home
  • or
  • Comprehensive damp checks required on a large home
  • or
  • Advice is required prior to extensive restoration or renovation of a sizeable or rambling period home
  • Severe dampness affecting the whole of a modest size home or up to half the rooms in a moderate size (3-5 bed) home
  • or
  • Widespread damp concerns on a moderate size (3-5 bed) home
  • Damp patches affecting a small number of rooms
  • or
  • Severe dampness affecting only 1 or 2 rooms
  • or
  • Widespread damp concerns on a modest size (1-3 bed) home
Interior checks carried out on: Entire house All indicated areas, plus those potentially vulnerable to damp All areas affected by damp patches, plus potentially vulnerable walls
Accessible roof spaces included Yes Only if there is evidence of possible leaks or damp
Checks for floor problems All floors Timber ground floors and floors in areas affected by severe damp Ground floors only
Checks for damp in walls Yes
Checks for timber decay Yes Interior timber only
Checks for salt contaminated plaster Yes
Exterior checks carried out on walls Yes
Checks for roof problems (subject to visibility/access) Yes
Checks for decaying brick and stone Yes
Checks for incorrect ground levels Yes
Checks for maintenance issues that could lead to future damp problems Yes Major issues only
Checks for previous building work that is incompatible with the house Yes Sizeable areas or areas where problems are starting to occur
Comprehensive report with prioritised advice Yes – printed and electronic (pdf) versions are both issued as standard Yes – electronic (pdf) version is standard but if preferred, a printed version can be issued instead
Standard Package price £2500 + daily travel £800 + travel £500 + travel

My travel for all damp surveys is based on the shortest RAC recommended route from my office at Aylsham in North Norfolk to the survey location. To give you an idea of what this is likely to amount to, here are some approximate travel charges for various locations: Norwich £15, Lowestoft and King's Lynn £45, Colchester and Peterborough £90, Lincoln £110.

Your next step is to telephone me on 01263 734815 for an impartial discussion about your damp concerns. Often a discussion is all that is needed to provide the pointers needed to resolve your concerns.

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