An Interview with Graham Coleman

Graham Coleman

B.Sc.,M.I.Biol.,C.Biol.,A.I.W.Sc.,F.Inst.R.T.S.

Graham has been in private practice as an independent consultant since 1982. He specialises in laboratory and consultancy services examining dampness, timber infestation and timber decay problems in the built environment. Graham is widely recognised as one of the country's foremost independent experts in this field.

During his career he has been called upon to investigate many interesting buildings and other structures including HMS Victory, The Great Hall at Westminster, King Arthur's Round Table in the Great Hall at Winchester to name but a few. Graham has had numerous papers published in technical journals concerning investigation of dampness, and measurement of moisture in building materials.

We are grateful to Graham for responding to our request for a brief interview the transcript of which is shown below. We recommend that you visit Graham's own web site which contains a great deal of interesting and useful information.
(See our links page)

PGA: What do you believe your function to be as an independent consultant?

Graham:
The function of an Independent Consultant is primarily to give objective, non-bias advice even if this does not support your client's view, which is frequently the case. I also believe that where possible it is essential to collect data - that is analytical results obtained from samples taken on site.

This forms part of the investigation and it is certainly an advantage if you can extract the data yourself. Being able to analyse materials yourself gives you a much better feel for the problem; over many years of such analyses one can get a good understanding for the materials but especially the problem. Far too many consultants still fail to collect sufficient and proper data where appropriate which can lead to unnecessary argument, litigation and expense in the longer term.

PGA: In percentage terms what is the approximate breakdown of your work between woodworm, dry rot and rising damp?

Graham:
Most of my work is directly damp related - rising damp, condensation, and plastering then followed by rots. Very little is related to woodworm but surprisingly one of the most common calls usually concerns Lyctus, the Powder Post Beetle.

PGA: If we could deal with damp related problems first, from your experience what is the most common reason behind an apparent failure of a remedial damp course?

Graham:
First of all it should be appreciated that an injection damp-proof course does not fail - they do not just work for a while and then stop working. They either work or are not effective from day one. Basically the reasons for 'failure' are a non-effective damp-proof course coupled with re-plastering specifications that cannot meet their required design function.

PGA: From your experience what are the main areas of misunderstanding or lack of knowledge in damp related problems?

Graham:
Condensation, especially in relation to relative humidity. Most people I come across do not understand relative humidity (RH) and its relation to temperature. Ask them, for example, which is the damper room - one at 60% RH or one at 50% RH and almost all will say the former. One needs to take temperature into account as relative humidity figures alone mean very little; you need temperature details as well to convert to vapour pressure - but that's another story.

PGA: We hear so much about 'correct re-plastering' following the installation of a remedial damp proof course. What is 'correct re-plastering' and why is it so important?

Graham:
"Correct re-plastering" in these circumstances is using a re-plastering system that will inhibit the passage of water and salts from the underlying wall to the surface. If the plasterwork cannot meet this function then it is of no use following the insertion of a remedial injection damp-proof course. If people appreciated that an injection damp-proof course is unlikely to stop rising damp like a physical damp-proof course and that walls take time to dry down then the importance of correct re-plastering would be better understood.

PGA: In your opinion is 'light weight renovating plaster' a suitable material to use following the installation of a remedial damp proof course?

Graham:
In over 25 years of analysing renders and plaster samples, I do find in general terms that dense sand and cement based mixes meet their design function. Renovating plasters, I have found, do not always meet this requirement. I believe the designers of such plaster have failed to appreciate that walls take time to dry down and that injection damp-proof courses will generally only control the rising damp, not stop it.

PGA: Very many surveyors use and rely on a 'Speedy' meter on site to evaluate the effectiveness of a remedial damp-proof course. What is your opinion of this?

Graham:
There are a couple of major problems to be considered when using a 'Speedy' meter on site. For example, they only measure the total moisture content; that is additional water ingress plus 'inherent' moisture held within the material. Inherent moisture is more accurately known as hygroscopic or air dry moisture and it is present in all masonry and timber based materials; it is the materials' standing level of moisture that is naturally absorbed from the air.

In some materials the hygroscopic moisture can be very high especially when it is contaminated with hygroscopic salts. So whilst a material may be damp, that dampness might all be absorbed from the air rather than from continued water ingress - this can lead to a wrong diagnosis as on site a Speedy meter cannot distinguish between hygroscopic dampness and water ingress. Thus an apparent damp problem may all be due to hygroscopic moisture absorbed from the air rather than actual water ingress. A further problem commonly associated with this instrument is the misconception that any material containing less than 5% moisture is perfectly acceptable - it probably isn't! 5% and less moisture can cause visual dampness and/or other spoiling problems. It is a nonsense, for example, to tell a client following a 'Speedy' test that the wall is perfectly acceptable at, say, 4% moisture content when the paper is peeling off, paint and plaster are erupting and timbers are rotting! In some materials moisture contents of less than 3% pose a problem. This 5% problem is going to be more clearly identified in the forthcoming Building Research Establishment literature.

Finally, it should be considered that a surveyor uses an electrical moisture meter to determine, for example, rising dampness during his initial survey. A new damp-proof course and re-plastering are recommended and undertaken. Three years later the client notices damp and calls back the surveyor. He tests the wall and obtains high surface moisture meter readings again on his electrical moisture meter. However, a 'Speedy' test gives him less than 5% moisture content, so he says this is perfectly acceptable.

The question now should be why are the high surface moisture meter readings acceptable now whereas three years earlier they indicated that the wall was sufficiently damp for a damp-proof course and associated works to be undertaken? Similarly, how does this man know that the high electrical moisture meter readings obtained three years ago didn't reflect the current less than 5% moisture content now found? Draw your own conclusions.

PGA: Are you able to cite any examples of misdiagnosis when a 'Speedy' meter has been used?

Graham:
Yes, I was involved in a case that illustrates these points very well. This was where a wall was damp-proofed and didn't dry out - it remained unusually damp. Various 'Speedy' tests taken from the wall over a period of time showed it was not drying out. It was thought to be an ineffective damp-proof course so further injections were undertaken periodically but nothing happened.

Eventually a full and proper moisture analysis was undertaken which clearly showed the damp-proof course to be fully effective - all the damp recorded by the Speedy meter was solely due to moisture having been absorbed from the air, i.e. hygroscopic moisture, in this case better known as 'salt damp'. All the moisture was being absorbed by huge levels of contaminant hygroscopic salts - it was not an ineffective damp course.

PGA: If we could turn our attention to timber treatment now. What is your opinion of current timber treatment insecticides compared with those used 15 to 20 years ago?

Graham:
Timber preservatives currently in use today have a significantly lower risk associated with them than those used 20 years ago. Just look at the LD 50 figures of the newer products - many have a lower risk in use than common household products.

PGA: Over recent years we have seen an increase in the use of what is referred to as fogging, misting or micro spray as a means of applying preservative on to timber. What do you think of these methods?

Graham:
This would mean writing a book on this subject. In essence fogs or mist distribute the material like smoke particles, and I do have experience of the latter. The problem is that one needs a given volume of fluid in order to penetrate a given volume of timber - the greater the volume of fluid the greater the volume penetrated. Mists and fogs are highly unlikely to deliver the volume on all surfaces which leads to significant under treatment. This, of course, has serious consequences for the client. Perhaps the answer to this question is more fully answered on my website.

PGA: Would you personally give a guarantee for this type of treatment?

Graham:
No!

PGA: Will a surface spray treatment alone protect against fungal decay?

Graham:
No! Penetration is limited on damp wood, and many rots can punch their way through minimally treated surfaces. Once into the untreated timber below the surface treatment the rot can spread unhindered.

PGA: What use therefore are so called 'dual purpose' insecticide/fungicide treatments and what protection do they offer?

Graham:
As a spray treatment 'dual purpose' preservatives are fine against wood boring insects but, of course, the fungicide fraction is not required in these circumstances. I have already expressed my comments on spray applied fungicides - basically they are of little value. Against Common Furniture Beetle and the like then one should use contact insecticide treatments only; don't waste money on 'dual purpose' materials. However, there is an exception to this and dual purpose solvent based fluids can be useful for injection into oak beam ends where there is decay and death-watch beetle, but don't forget to try and dry down the wood first to control the rot.

PGA: What do you think of the Health and Safety Executive (HSE) registration procedure in this country for timber preservatives?

Graham:
The registration process in this country is excellent and the clearance procedures for any pesticide products are such that we probably have the safest pesticide industry in Europe, possibly the world. What people fail to appreciate is the strictness of the clearance scheme. In essence all products, pesticides and raw materials are thoroughly evaluated by the Government's Advisory Committee on pesticides, a body of very eminent independent scientists drawn from a number of specialisations.

They evaluate all toxicity and other related data pertaining to the formulation. Labels, hazard warning phrases, etc, are also scrutinised before clearance for 'use as directed' is given. To use a product without such clearance is a criminal offence. There is very strict legislation laid down in relation pesticides, the most important being under the Control of Pesticide Regulations, part of the Food and Environmental Protection Act.

PGA: You read articles in the press stating that timber treatments are 'toxic'. What do you think?

Graham:
No timber preservative used in the domestic market carries a 'toxic' label (skull and crossbones symbol on the can). Most are labelled 'irritants' under the current legislation (St Andrew's cross hazard warning label) and that is often only in their concentrate form. A number of the ready to use timber treatment materials do not require a warning symbol at all! Compare this with the warning symbols on common household products such as fabric conditioner and bleach.

Those in the press that peddle the toxic notion never advise the public of the Control of Pesticide Regulations, part of the Food and Environmental Protection Act. Indeed, some of these people are distinct self-publicists and have distinct agendas and it is clearly not in their interest to report the full facts.

PGA: What do you understand to be 'dry rot treatment' and does it ever fail?

Graham:
Graham: The industry's understanding of dry rot treatment appears to be masonry irrigation, i.e. treating walls to kill invading fungal growth. Unfortunately many rely far too heavily on this treatment, and yes, it does fail frequently. A leading authority on dry rot once said that such treatment works best where it is not required. Enough said?

PGA: What is your opinion of the 'free' or low cost survey of a property for timber defects and rising damp that is common practice in the industry today?

Graham:
The free or low-cost survey is neither free nor low cost - someone at some time will have to pay the costs involved. There is always the argument that a company will always find a problem to get work; in a number of cases this is undoubtedly true. But then again so do dentists, solicitors, etc. - they will only receive a fee if they diagnose and treat a 'problem'. Nevertheless, it is probably the best policy to go for the paid survey since it may be argued that the investigator is less inclined to be touting for work.

PGA: How do you see the future of the building preservation industry in this country?

Graham:
I see the industry declining slowly as a whole. We will probably be left with fewer practitioners but overall a better qualified and higher quality industry.

PGA: Thank you very much Graham for your time which is very much appreciated. We hope that your views and comments will be thought provoking and provide information to interested parties.

Graham has a very interesting web site that is well worth a look. A link to his site may be found on our links page.