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Article 6 - Rising Damp - The Truth not the 'Myth' PDF Print E-mail

An informed article written by Graham Coleman which explains the truth about rising damp and dispells the ilinformed theory that rising damp does not exist which is peddled by those whose only agenda is self publicity.

 

RISING DAMP - THE TRUTH, NOT THE 'MYTH'

 

By: G R Coleman B.Sc.(Hons). M.S.B., C.Biol., M.I.W.Sc., F.Inst.S.S.E..

 

People reading this piece will probably be aware there have been numerous articles in both the press and some professional journals regarding the actual existence of rising damp.  Indeed, there has even been a small published book stating that rising damp is a myth. We are even told that the term 'rising damp' originated in the 1960's but unfortunately for that author it appeared long before - the term was used in the British Medical Association Journal of the 1870's.  So what is the truth?  What is the objective evidence for rising damp?

 

For a start, it is not a simple UK phenomenon as some publications would imply.  Serious peer reviewed papers have appeared in scientific building and technical journals for many years in those parts of the world where rising damp has proved to be a problem. This includes not only the UK, but Belgium, Italy and especially Australia where it is referred to as 'salt damp'. It occurs where any masonry is sufficiently permeable to take up water from the ground. Given this fact it is unlikely that Governments and Technical Institutes in these parts of the world would spend time and money on something that was considered to be a 'myth' - unless one believes in international conspiracy theories!

 

We can define rising damp as water rising up through masonry - the water originating from the ground. The water rises via interconnecting pores within the wall by a process we refer to as 'capillarity' - in other words permeable masonry acts somewhat like a wick. However, the wick idea is not quite that simple.

 

In order for water to rise the pores up through wall must be interconnecting.  If the capillaries are sufficiently fine and interconnecting then water has the potential to rise.  Pores in masonry are reported to be as small as 0.001 mm in diameter, but on average are around 0.01 mm. Pores of this latter size give a theoretical height of rise of 1.5 m.  However, processes such as evaporation and pore continuity will in part control this.

 

Even now it is still not that simple. Think of the capillaries within the wall as a 'suction' agent, and similarly think of the ground as the same.  If the suction of the wall is greater than the suction of the ground then water will rise if the capillaries are of a suitable size and sufficiently continuous. If, however, the suction of the ground is greater than the wall then water will not rise even if the pores within the wall are continuous. Put quite simply it explains why not all walls without the benefit of the damp proof course will have rising damp. There are simply a number of factors which need to be present for water to rise. Hence, many properties without physical damp proof courses will not have, and probably never will have rising damp.  So simply taking an old Victorian wall and standing it in water to see if rising damp occurs as one individual has done proves precisely nothing whatsoever if the water doesn't rise, and  as such it is not a basis on which to 'prove' that rising damp is a myth as this individual has indicated.

 

We have defined the rising damp above.  Where it occurs water rises up through the system of interconnecting pores to a given height depending on pore structure, evaporation and other factors: this process is continuous and will take place over many years.

 

Ground water contains soluble materials, a proportion of which are soluble salts; these are usually presents in lower parts per million and at this level they are of no significance.  A proportion of the salts are soluble chlorides and nitrates neither of which exist in building materials at any significant level, usually less than 0.01% so effectively we may consider the materials to be free from such salts.

As water rises from the ground into the wall these dissolved salts are carried in the rising water.  As the rising water continues to rise and evaporate these salts are left behind, and over many years significant levels become deposited within the wall and finishes.  The majority of the salts are deposited towards the maximum height of rise of water where they form a distinct concentration known as the 'salt band'.  Since these salts are, for practical purposes, absent from bricks, mortar, stone, plaster, etc, it is their presence and distribution that is the key to the diagnosis of rising damp.  Whilst there are a few occasions where such salts can arise from other sources, by far the most common occurrence of these salts in walls is water rising from the ground.  In examining a wall therefore suspected to be affected by long term rising damp one will readily find these salts but only up to the height of the rising damp - above the height of rise these salts will effectively be absent.  So looking for the presence and distribution of these salts, especially in relation to the presence and distribution of water ingress, is essential for a definitive diagnosis, and it is this fact that the supporters of the 'myth' conveniently ignore.

 

To reiterate the fact - the salts and their distribution are the key to diagnosis together, of course, with whether or not water is still entering the wall.  Moisture and salt 'profiling' will readily identify the presence of rising damp in relation to any other form of dampness. Condensation, surface or interstitial, never introduces ground water salts into the wall neither does rain penetration. In the case of condensation in the UK there is a 'condensation season' and this is broadly between October and April. If there is dampness outside of this period it is probably not condensation.  Furthermore, unlike rising damp, condensation is very frequently intermittent and if so it may not remain sufficiently long to cause any visual problem.  If it is long term then it is clearly readily evident. It is unlikely therefore that condensation will be misdiagnosed as rising damp especially considering that surface condensation literally forms on surfaces and will penetrate permeable surfaces only a few millimetres if the condensation is severe. Effectively condensation is highly unlikely to occur during the warmer months of the year

 

Another misconception is the classic "mains water leak" where the rising damp is supposed to be caused by such a problem with the water soaking the ground. Basically, if the wall has sufficient suction water will rise from the ground whether there is a leak or not. Indeed, the most common source of water in the ground is rainwater where it clearly wets up the upper surfaces of the ground, i.e. where the walls are in contact with the soil.

 

Physical damp proof courses were introduced into 'Regulations' in the 1870s in relation to public health although some properties were built with such damp courses prior to this time.  However, it took a number of years before all properties were built incorporating physical damp proof courses.

 

So how common is rising damp?  It is very unlikely, but not absolute, that properties with physical damp proof courses will have rising damp unless it becomes bridged or seriously defective, the former usually being readily identified.  Of the properties that do not have a damp proof course some may have rising damp, others may not: not having a damp proof course is not synonymous with having rising damp.

 

Building Research Establishment positively identified rising damp to a greater or lesser extent in around 80% of the properties they investigated in Cardiff several years ago. These results together with other data suggest that rising damp is probably not that uncommon in United Kingdom (it is sufficiently common in Denmark, Belgium, Italy and Australia for the Institutes to research and report on the problem, especially in relation to their historic buildings). However it appears likely that severe rising damp is sufficient to cause significant decorative spoiling, staining, blowing of plaster and timber decay

 

So does rising damp exist? - A resounding yes!  Can it be readily diagnosed? - yes, it has very distinct features not present in other forms of dampness, but it may take laboratory facilities for a positive identification.  Is rising damp a myth? - no, and certainly not in Europe and Australia.

 

 
Contact Peter: Email - info@dampdecay.co.uk - Telephone: 015242 71794