Historical Context of the Rising Damp Problem
Rising damp has been affecting old buildings since antiquity. It has been definitely known and documented by the Romans who also worked out solutions to mitigate it, by creating and using special plaster mixes.
The Roman Period was followed by barbarian invasions, leading to the formation of fortified towns across Western and Northern Europe; these town-fortresses being called "bourgs" (later boroughs) and their inhabitants "the bourgeois".1Gies, Joseph (1969): Life in a medieval city, Arthur Barker Publishing, New York
During the Middle Ages the cities of Europe were full of cattle barns and pigsties, with workshop clustered around churches, castles or bishops' palaces. Although very little are known about "medieval houses" as very few of them have survived (mainly 13th century towers), it is believed that during the "dark" middle ages along with generally low hygiene standards and poor health conditions damp buildings were the accepted "norm".
Starting from the Renaissance Period (late 15th / early 16th centuries) a lot more is known about life in important European cities.2Saalman, Howard (1968): Medieval cities, New York, Braziller Later, modern historical records have consistently documented rising damp starting from the 1840s. Please see below some period publications confirming that problems caused by rising damp were well known in Victorian England nearly 200 years ago, showing significant damages to existing 16th - 17th century cottages and country houses.
Click on the titles below to expand the content.
This American book published in 1851 discusses important aspects of house building in the United States: design, materials used, finishing, heating & ventilation etc. The problems of dampness is also addressed, highlighting the importance of damp courses (or the use of hydraulic mortars) to prevent dampness from rising.
The book also discusses in details most building materials used in the 19th century, highlighting that stone houses built without a damp proof course are more or less damp...
... and common lime mortar will not stop rising damp from the ground.
"The foundation of walls built of common lime mortar, will always be damp, from capillary attraction - common lime mortar offering no impediment to the absorption of the moisture from the soil, or to its gradual passage upwards into the main wall of the house."
This book published in 1870 presents 45 private residences of its time, focusing on practical aspects of house building, including: how to properly build walls, construct floors, roofing, ventilation, drainage, what materials to use etc.
The problem of dampness is also discussed in detail, with practical advice on how to prevent it, overcome it and build a dry, comfortable home. Rising damp must always be addressed by laying a damp course under every wall, whether internal or external.
"Damp course: a provision should always be made to prevent any damp rising up the walls from the foundations."
This book published in 1905, presents examples of typical domestic buildings, including some of the most noteworthy houses from Victorian England. The book highlights damages caused by rising damp in many old 17th century cottages - making some rooms almost unusable for living.
"... When the houses were built in sloping sites... by means of terraces and steps... these lower rooms, owing to wet and damp, are now almost unusable except at store places."
The reason why the ground floor rooms of many old cottages were wet and unhealthy, especially during winter time, was lack of damp proof courses, an unknown technology at the time when these cottages were built.
"The ground floor... laid directly on earth, with the result that the moisture readily soaked through, doubtless causing the rooms to be wet and unhealthy, and as damp proof courses were unknown when these houses were built, the lower part of the walls in winter time was moist and damp."
This book published in 1909 highlights the damp, disused condition of some rooms in old cottages due to dampness and lack of damp courses in those buildings.
"Also the houses are often built on a slope, and the lower rooms are so damp that most of them are now disused. The stone floors, indeed, were laid direct on the ground, damp courses were unknown, so no wonder that the houses were not dry."
This book published in 1914, dealing with the restoration of old houses - weather cottage, farm house or small manor house - presents is detail the history, problems and restoration challenges of 40 old buildings stretching back 5 centuries.
Problems caused by rising damp are repeatedly highlighted, linking the problem and associated damages to lack of damp proof courses, unknown when these buildings were originally built. Several such examples are presented, and poor workmanship is also mentioned.
"Some people are apt to suppose that the buildings of historical periods were constructed on particularly sound lines. That, however is hardly the case. It is to the nineteenth century that we owe the use of such devices as damp-courses, and the lack of them in early buildings has not only shortened their lives, but many many of them uninhabitable, sometimes beyond redemption."
Some repairs followed the principles laid down by the Society for the Protection of Ancient Buildings, the SPAB, already in existence since 1877. The book praised the SPAB's rigorous work and conservative approach in retaining as much old building fabric as possible. At one building the repair works also included the insertion of a solid damp proof course while undertaking some foundation works.
"...the principles laid down by the Society for the Protection of Ancient Buildings. It is not only conservative in the preservation of every scrap of old work, but eminentlv satisfactory in appearance. For the needful repairs to the walls bricks were made locally of the same size as the old ones. The attitude of the S.P.A.B., familiarly known as the Anti-Scrape, is sometimes more rigorous in respect of the alteration of old buildings than some antiquaries can endorse. Its work has been of immense value, however, in forming public taste and in checking the vandalism which raged unhindered before the Society was formed."
This book published in 1915, written by the Medical Officer of Somerset County, discusses important aspects of rural housing, including: the housing shortage, housing conditions, health and sanitary problems etc. The effect of various types of dampness are discussed in detail, based on the findings of professional surveyors.
"A very considerable proportion of country cottages are damp... due to a combination causes. One prevalent cause is the absence of proper foundations and damp-proof courses. There is nothing to prevent the wet from the earth rising up the walls, and it does so rise."
Rising Damp is listed as a major problem that can be remedied with difficulty. The solution is fitting a solid DPC while other works are being undertaken. Failing to do so, the lack of a damp proof course, often makes old buildings uninhabitable, also resulting in their long-term decay.
"The provision of a damp course... is an expensive and troublesome matter. It has to be inserted... to prevent houses from being condemned." (Def: condemned: officially classed unfit for living)
Conservation vs. Damp Proofing Approach
Dampness is one of the major causes of decay in old buildings, as a result the efficient and conservation-friendly handling of rising damp should be an integral part of building conservation technology. Yet, damp proofing - which in Britain is synonymous with chemical DPCs - has a bad name in conservation circles because mainstream damp proof course technologies are:
- Invasive: causing significant changes or damages to the historic building fabric (e.g. by drilling) which they supposed to protect.
- Non-breathable: the replastering following the insertion of a damp proof course is done with non-breathable sand and cement plasters, known to create additional dampness problems.
As a result, the validity of damp proofing has been questioned by conservation bodies, forbidding their use in many listed buildings. Lack of modern research on rising damp, by not understanding its mechanism or its primary drivers, lead to incorrect or short-term solutions that gave only temporary relief from the problem without solving it long-term.
All rising damp solutions on the market - regardless of their approach or long-term effectiveness - can be divided into the following four solution categories:
1. Installing an Injected DPC
One of the common recommendations to solve rising damp - often a clause to receiving a mortgage - is fitting a chemical or injected DPC. Although mainstream, this solution is not considered conservation-friendly due to its invasive nature, regardless if an old building is listed or not.
2. Applying Various Moisture Barriers
The application of any non-breathable waterproofing materials (plastic membranes, cement-based plasters, tanking slurries, bituminous layers, waterproofing paints etc.) onto the wall surface, to keep moisture away from the surface. These can be applied on their own or in conjunction with a chemical DPC (at point 1).
This again is not a very conservation friendly approach. Although with this solution the wall surface stays dry, moisture keeps accumulating invisibly behind the surface until eventually resurfaces (often years later), resulting in a significantly damper and more decayed wall fabric long-term.
3. Focusing on Breathability Alone
This is the "official" conservation-friendly approach. The general consensus is to leave rising damp alone, instead one should focus on making the wall fabric breathable with actions such as: using lime plasters, removing any cement and non-breathable materials (in fact reverting any moisture barriers applied at point 2), improving the drainage, more ventilation and heating etc,
This is all good advice which will improve many old buildings, however in reality none of these actions solve rising damp long-term. Why? Because they don't address its primary cause: the evaporation of moisture from the soil into the core of the building fabric. Additionally, there seems to be a considerable divergence of opinions, even among conservation professionals, about the mechanism and drivers of rising damp, leading to inconsistent advice about its handling.
The latest technical research data below should bring more clarity into this subject. Click on the title below to expand more information.
What is Rising Damp?
Rising damp is the natural upward movement of moisture from the ground inside porous masonry. Latest research has shown that rising damp is NOT just liquid moisture movement (capillary action) but a significant part of it is saturated vapor movement - rising damp being a COMBINATION of vapor and liquid movement.
In nature there is a constant, ongoing evaporation from the soil into the air and the surrounding environment.
When a wall is built onto the soil, blocking the free evaporation of moisture into the air, the moisture will now evaporate INTO the porous wall fabric, into the wall capillaries. In the presence of humidity, the tiny capillaries, having an extremely small volume, become instantly saturated with moisture. The humidity saturated environment triggers a special form of condensation driven by the excess humidity (which is independent of temperature), resulting in a thin liquid water film on the capillary surfaces, which can gradually grow into standalone capillary flow.
This is a STANDALONE mechanism (consisting of several vapor and liquid transport mechanisms, as shown above), that can develop and exist independently of any other dampness sources. It can be reproduced and observed in a lab and in real buildings. Its development has been well documented by the scientific literature worldwide.
Any additional problems or building defects arising from lack of maintenance or neglect - such as improper pointing, higher ground levels, lack of heating, cement plasters, non-breathable materials etc. just to name a few, very often present in old buildings - do not cause rising damp if the ongoing evaporation from the soil is not already present. These problems create their own set of issues, overlapping rising damp. Fixing these problems will obviously improve the overall situation, but if rising damp is also not addressed on its own, as per below, it will continue to exist and create problems (years) later.
A very important but often less known or neglected aspect of rising damp are ground salts. The rising water flow draws up dissolved salts from the ground, depositing them into the building fabric. Following the evaporation of water, salts crystallize, expanding 5-10 times in volume. The exerted mechanical expansion pressure (crystallization pressure) leads to the cracking, crumbling and flaking of the plaster and wall fabric – which is a consequence of rising damp.
Crystallizing salts are the primary cause behind crumbling and the gradual, slow decay of masonry. Because over decades or centuries salts become a permanent part of the building fabric, their presence must be known and “managed” by using appropriate renovation materials.
The Main Moisture Sources Affecting Old Walls
Thus, the main dynamic forces affecting old walls are:
1. Water in from the soil (rising damp): the evaporation from the ground is a major source of moisture in old buildings. The soil, which is in connection with the water table, is one of the most abundant sources of moisture, which can result in several liters of water per day being evaporated into the living area.
2. Water out (evaporation - breathability): the moisture that gets from the soil into the building fabric travels upwards and sideways, trying to evaporate out into the surrounding environment.
If evaporation can happen freely (e.g. by using breathable lime finishes), a good part of this moisture is able to evaporate out, keeping the wall fabric relatively dry and the surface completely dry. However, even under perfect breathability conditions, some part of the moisture is still trapped by the building fabric due to the presence of surface charges (electrically charged capillary surfaces attract water vapors), which leads to a gradual slow accumulation of moisture inside the wall fabric, long-term developing into a rising damp problem that eventually needs attention. This mechanisms has also been confirmed by lab experiments.
On the other hand, if evaporation is hindered (e.g. by non-breathable (cement) plasters, membranes or any modern materials acting as moisture barriers) the moisture build-up inside the wall fabric occurs much faster, resulting in significantly more moisture, that creates more damages faster.
Finally, often there is a third dynamic force at play:
3. Water in from other sources: any other moisture source than rising damp, primarily various forms of rain water (e.g. as water splashback, leaky drains or gutters, water ingress around chimneys, pointing and rendering problems etc.) - often present due to building defects or general lack of maintenance. Occasionally, broken water or sewer pipes, can also create rising damp symptoms, but these are limited to smaller areas and can be quite intense in nature.
Because liquid water ingress is generally a more abundant source of moisture than the "slow" rising damp, when present it can completely overlap or mask the underlying problem of rising damp. Fixing these defects obviously brings about an (often significant) improvement, but the underlying rising damp, if also not detected and addressed, it will continue to create problems.
The amount of existing moisture inside old walls is determined by the dynamic balance of the above three factors (rising damp, breathability and other moisture sources), which can all show seasonal fluctuations.
The soundness of this technical data can be validated on many old buildings - especially on large old buildings with thick walls with difficult to handle severe rising damp problems (e.g. churches, cathedrals, manor houses), where all known "fixes" such as drainage, heating, ventilation, lime plastering etc. have all been exhausted - often with no expenses spared, under the careful supervision of experienced conservation professionals - yet the problem of rising damp remained, the plaster needing periodic repairs or replacement.
The missed problem here is the presence of soil evaporation inside the walls, the main cause of rising damp, which over time, no matter how breathable the wall fabric is, always leads to moisture accumulation inside the fabric and subsequent plaster damage.
Plaster damage in old buildings, most commonly is a consequence of a dampness problem, which needs to be investigated and handled. Just automatically replastering with lime won't solve the problem because the underlying dampness will again damage the new plastering. The never-ending replastering cycles in old buildings, where the plaster "keeps falling off" every few years, is a definite sign of an unsolved underlying condition (very often rising damp).
Breathability is Only a Partial Solution
Breathability (letting moisture out) is only half of the solution to any dampness problem, the other half is preventing the moisture from getting in. The concept of breathabilty works well for walls, because they are affected by dampness (mostly various forms of rainwater) intermittently. When it doesn't rain, the walls can "breathe out" the moisture and gradually recover.
The situation of rising damp is different. Evaporation from the ground is present constantly present, non-stop, 24/7 as the soil under the walls is always damp, with no option for the base of the walls to "catch a break" to dry out. Thus, for the problem to go away, the soil evaporation into the wall fabric must be interrupted. For rising damp, this is achieved with a damp proof course. The primary role of a damp proof course is to become a protective vapor barrier from the ground.
Why no one is concerned about the breathability of new(er) buildings? Because those have a good damp proof course so their fabric is dry. In lack of moisture there is nothing to breathe out. Breathability becomes a concern after the fabric gets damp, and it becomes the "prime dehydration solution" when there is no other way to get rid of the moisture.
4. Non-Invasive Magnetic DPC Technology + Breathable Lime Plastering
This is the solution that combines a non-invasive approach with breathability, being the ideal solution for any old or listed building.
Recent technical research into the nature of rising damp and molecular phenomena occurring in masonry lead to new technological breakthroughs: the magnetic DPC. This solves the problem of rising damp non-invasively, without any damage to the building fabric. Pairing this solution with a knowledge of traditional lime plasters, salts and natural pozzolans results in a sympathetic solution, that ticks all the right boxes, resulting in an ideal solution with no known negatives that can last for decades.
Old building owners can choose any of the above 4 approaches, and they should choose the solution that makes most sense to them.
Solid damp proof courses (made of slate, tar, bitum or modern membrane), despite their invasive installation, provide the best protection against rising damp, outperforming chemical injections by a wide margin.3Harmathy, Norbert & Jaksic, Zeljko & Trivunic, Milan & Milovanovic, Vesna. (2014). Rising damp analysis and selection of optimal handling method in masonry construction. Periodica Polytechnica Civil Engineering. 58. 10.3311/PPci.2113
In the UK, during Victorian times, at the turn of last century, many old buildings have also been retrofitted with solid DPCs, according to historic records. Those slate or bituminous DPCs fitted over a century ago have now aged, reaching the end of their service life, rising damp becoming an increasing problem in many Victorian buildings. When building listing - adding buildings of special interest to a List to protect them from alteration or demolition - came into effect after the 2nd World War, the retrofitting of solid DPCs as a potential solution has been stopped, leaving the problem of rising damp largely unsolved. Recent academic research papers4Franzoni, Elisa. (2018). State-of-the-art on methods for reducing rising damp in masonry. Journal of Cultural Heritage. 31. 10.1016/j.culher.2018.04.001.5Franzoni, Elisa. (2014). Rising damp removal from historical masonries: A still open challenge. Construction and Building Materials. 54. 123-136 came to the same conclusion, that rising damp, especially in historic buildings, is still a largely unsolved problem.
The Correct Solution
With a better understanding of the mechanisms of rising damp, the solution becomes much simpler, and it consists of the following two steps:
Step 1 - Installing a DPC
The primary role of a damp proof course (DPC) is to become a vapor (and liquid) barrier, to stop or minimize the excessive evaporation of moisture into the wall fabric - the primary problem, that makes rising damp a never-ending problem.
This can be achieved by physical, chemical or electromagnetic means. Several DPC technologies exist on the market, including non-invasive magnetic DPCs.
Step 2 - Breathable Renovation
To repair the damages and to ensure a long-lasting finish, a certain amount of renovation is usually necessary.
Damages of the plaster - the secondary problem - is a direct consequence of the underlying rising damp problem. During renovations special attention needs to be paid to mitigate the effect of salts. Due to the presence of ground salts absorbed into the masonry, the plastering solution MUST include a salt-barrier to prevent the premature breakdown of the new plaster.
Let's look at both of these steps in more detail.
|1||Gies, Joseph (1969): Life in a medieval city, Arthur Barker Publishing, New York|
|2||Saalman, Howard (1968): Medieval cities, New York, Braziller|
|3||Harmathy, Norbert & Jaksic, Zeljko & Trivunic, Milan & Milovanovic, Vesna. (2014). Rising damp analysis and selection of optimal handling method in masonry construction. Periodica Polytechnica Civil Engineering. 58. 10.3311/PPci.2113|
|4||Franzoni, Elisa. (2018). State-of-the-art on methods for reducing rising damp in masonry. Journal of Cultural Heritage. 31. 10.1016/j.culher.2018.04.001.|
|5||Franzoni, Elisa. (2014). Rising damp removal from historical masonries: A still open challenge. Construction and Building Materials. 54. 123-136|