Rising Damp – Historical Overview
Although the existence of rising damp and problems caused by it have been documented since antiquity, its underlying mechanisms has not been well understood.
The first known written historical reference about rising damp goes back to ancient Rome. The Romans, being excellent engineers, that have built some masterpieces that lasted over 2000 years. Historic records show that they not only were aware of rising damp, but they also worked out efficient solutions in combating it.
"I shall next explain how the polished finish is to be accomplished in places that are damp, in such a way that it can last without defects. First, in apartments which are level with the ground, apply a rendering coat of mortar, mixed with burnt brick instead of sand, to a height of about three feet above the floor, and then lay on the stucco so that those portions of it may not be injured by the dampness."
The Victorian Period
From 1877 the use of damp proof courses became mandatory in the UK, however references in books and specialist publications mentioning rising damp go back as early as 1844. Here are some historical references from the UK describing the existence of rising damp, along with recommended solutions on how to overcome it.
Click on each publication to expand additional details.
The Builder was a journal of architecture published between 1843 and 1966. Issues from year 2 (1844) mention dampness rising from the ground due to capillary attraction. As a solution, to prevent the ascent of moisture up the walls, it recommends the use of slate inside the walls.
This professional textbook from 1851 is a practical manual written for architectural students, engineers, contractors and builders.
Dedicating a whole chapter to dampness, including to the prevention of rising damp, stressing the importance of separating the foundations from the rest of the wall with a damp proof course, to stop the upward migration of dampness.
"... to intercept entirely all communication between the foundation below and the walls above, no damp, as far as we have observed, can possibly find its way upward; and however damp the work below the asphalte (DPC) may become, that above will remain perfectly dry and unaffected."
French architects, independently, came to the same conclusion. Even if the footing of a building is always underwater (e.g. in a lake), using less than half an inch thick asphalt DPC keeps the walls completely dry.
This paper read on 12 Jan 1863 at the General Meeting of the RIBA, discusses the sanitary aspects of rising damp in old buildings, and various damp proof course options as a natural remedy to the problem - about 20 years ahead of global UK sanitary reforms,
"The great evils, in a sanitary point of view, are doubtless caused by damp rising up the walls by capillary attraction. (...) Our remedies for this have generally been a layer of asphalte throughout the thickness of the walls, "sheets of lead", a course of slates bedded in cement, and sometimes compounds of gas-tar, pitch, sand etc."
A new damp proof course is also presented to the attending architects - a layer of perforated bricks, laid as a row of ordinary bricks, to prevent the rise of moisture, while also improving underfloor ventilation.
Some of the architects' comments on this damp proof course technology included:
- Many new inventions are adopted with difficulty, including the idea of damp proof courses.
- Some concerns about their additional cost. Damp proof courses have often been skipped to save on material and labor costs.
- They should be better tested, although in buildings used (e.g. the great Artillery barracks at Colchester) they were very efficient.
- Their aesthetic look is a positive.
- Architects were in agreement that damp proof courses were the best method of keeping damp down.
A report of the British Medical Journal dating 20 Dec 1873 discusses various sanitary aspects of rising dampness in houses, hospitals and public institutions.
Various damp proof course technologies used by architects are mentioned in the paper, including double course slates, Welsh slate bedded in cement, sheets of lead, hot asphalt DPCs, glazed bricks and vitrified stone-ware tiles.
The paper also advises the retrofitting of a damp proof course into old buildings, which turned uninhabitable buildings into perfectly healthy ones.
This 3-volume publication from 1876 was the official syllabus of a three-part advanced building construction course. A whole chapter is dedicated to the problem of dampness and how to efficiently overcome it, including rising damp, penetrating damp and falling damp from the roof or gutters.
Various damp proof course technologies are also discussed, making reference to the fact that slate DPCs embedded in cement are liable to crack and thus fail.
Glazed pottery slab damp proof course built into the wall:
Lastly, according to an official report from the 1867 Paris Exhibition, some interesting technical facts from the book on how much water saturated brickwork can hold:
- In England, common bricks can absorb as much as a pint or pound of water
- An ordinary cottage consisting of 12,000 bricks, can hold about 6.5 tons of water when saturated
- Porous sandstone fit for building purposes may contain about half a gallon of water per cubic foot. (about 80 liters / m³)
Realizing the effect of damp walls onto the health and well-being of inhabitants, between the 1870s - 1890s a number of health bills have been passed throughout UK, all of them recommending damp proof courses as a means to combat capillary rising damp.
"We must now turn our attention to the walls, which is equally necessary to protect from rising damp. If you plant a brick or stone wall o ground which is capable of retaining moisture, it will inevitably happen that unless you take means to stop its progress, the moisture will climb up the walls in obedience to the law of capillary attraction."
Solution to the problem is a vitrified (glass-like) layer of bricks or two layers of slate.
The book also provides technical advice with drawings, presenting the wrong way of laying a slate damp proof course">, if gaps are left between them.
Clause 96 of the The London Public Health Act from 1891 stipulates the use of damp proof courses for underground rooms: "Any underground room (...) shall not be let or occupied unless (...) every wall of the room is constructed with a proper damp proof course">."
Capillary Action Theory - A Historical Mistake?
Rising damp has been commonly associated with capillary action: liquid moisture rising from the ground as in a capillary glass tube. Then, according to some other theory, water can be made to rise in old walls by strong water pressure (e.g. from water pipe leaks), driving humidity up the walls. Either way, the main cause of rising damp has been thought to be liquid water.
Rising damp as capillary action is mentioned in several historical publications as early as 1844.
The view that rising damp is capillary action has been brought forward from the past into today without anyone investigating in detail weather this is true or not. As a result, solving rising damp in old buildings has focused on handling liquid moisture: either by channeling it away from the building (drainage) or preventing it from penetrating the building fabric (fixing any leaks, good pointing, rendering etc.).
Recent technical research into breathability – how moisture moves in-and-out of old walls, what drives it etc. – has uncovered that a fundamental error was made in the past assuming that rising damp is capillary action. The mechanism of rising damp is different - it is not capillary action.
The Mechanism of Rising Damp – Simple, Non-Technical Explanation
In nature, there is the natural Water Cycle that describes the large-scale circulation of water in nature. Liquid water falls as rainwater, goes into the ground, then evaporates and rises up as vapors. As part of this cycle the soil constantly evaporates moisture into the air.
When a wall is built onto the soil – blocking the free evaporation of moisture – the moisture from under the wall will now first evaporate INTO the porous wall fabric (into the wall capillaries), then into the air. In other words the full evaporation path becomes: Soil >> Wall fabric >> Air.
However, according to measurements, even in the case of a perfectly breathable wall fabric (e.g. bare bricks built with lime, with no moisture barriers present) not all moisture evaporates out from the fabric. Some part of moisture gets trapped by the building fabric due to surface attraction and it starts accumulating, going through several stages: from vapors, to a thin liquid film, to partial capillary flow, eventually developing into full capillary flow – as shown below. Capillary action is the last stage of this cycle.
The primary mechanism of rising damp is VAPOR MOVEMENT from the soil as a result of natural soil evaporation.
Vapors rise and so does humidity. The rise of vapors from the soil under the building results in a gradual slow accumulation of moisture that over time can become so severe that it needs attention. This is the fundamental mechanism of rising damp.
Salt efflorescence, the crumbling of plaster, tide marks etc. are just some of the typical signs accompanying the problem, the accumulation of moisture. Which of these signs are present in an old building can vary widely depending on a number of variables such as the intensity of soil evaporation, type of plaster on the walls etc.
The Mechanism of Rising Damp – Technical Research Data
For those interested, here is some more insight and technical data on rising damp. We have done a series of experiments both in the lab and on real buildings. This experiment performed in a controlled lab environment shows in detail the development of rising damp and its primary drivers.
Experimental Setup and Methodology
We have built a small wall consisting of 4 bricks. Instead of mortar we used dry brick dust from the same bricks, a common practice for lab simulations.
The bricks were placed on a 100 mm thick well-drained but humid soil-bed placed in a deep perforated tray, positioned in a second, shallower tray used to control the amount of water vapors present under the bricks, with precise wetting of the soil from the bottom.
Detailed measurements have been taken during the experiment using an array of embedded micro-sensors, collecting humidity and temperature readings from the soil, mortar courses, depth and surface of the bricks as well as of the ambient environment. In addition, various electrical parameters of the fabric such as the spontaneous voltages and currents present in them have also been recorded.
The readings have been taken by an 80-channel Keithley Tektronix DAQ-6510 professional data logging system operating at 0.0025% accuracy.
The experiment has been divided into 2 stages:
- Stage 1: Natural soil evaporation (drying soil): aimed to understand to what extent a drained soil with no liquid moisture in it (and no capillary action) affects the moisture content of the building fabric.
- Stage 2: Controlled wetting of the soil (damper soil): aimed to understand how the increased evaporation from a rising water table affects the moisture content a wall.
Stage 1: The Effects of Natural Soil Evaporation
Once the soil sensor is inserted into the soil, it starts registering the moisture content of the soil (black line). When the plastic foil is pulled from under the bricks – acting as a damp proof course at the start of our experiment – vapors now can freely start evaporating into the first brick. (see Graph 1)
As a result, in depth the brick starts accumulating moisture (dark blue line). The humidity on the surface of the brick (light blue line) however stays at the level of ambient humidity (orange), around 36% RH.
Let’s fast forward 10 – 11 days into the experiment. During this time the damp soil was naturally collecting humidity from the soil. Some interesting observations at this stage (see Graph 2):
- The moisture content of the soil (black line) under the bricks gradually increases, peaks then slightly declines as the surface of the soil starts drying out.
- The depth moisture content of the lowest brick (dark blue line) increases from ambient 36% RH (orange) to about 87% RH. This shows that the amount of moisture present in a well-drained drying soil is more than enough to wet the bricks sitting on it. Imagine what a soil constantly wetted by rain can do (more on that next). As a result, drainage will not solve rising damp, although often improves the situation, especially in case of clayey soils.
- We can also see that the surface and the depth of the bricks behave differently and have different drivers: the surface of the fabric is driven by ambient humidity (orange line), while the depth of the fabric is driven by the soil humidity (black line). (see Graph 3)
- Ambient changes barely impact the depth of the fabric indicating that the effect of surface changes is negligible in depth.
This concludes the first stage of the experiment.
Stage 2: The Effects of Soil Wetting
Next, 12 days into the experiment we applied liquid water at the base of the 100 mm thick soil bed under the bricks, simulating a more intense soil evaporation from an increased water table (e.g. from rain).
The changes caused by the increased evaporation can be broken down into several smaller phases (see Graph 4):
- Phase 0: Before soil wetting: Stage 2 starting point. The drained soil has been freely evaporating into the wall fabric for over a week.
- Phase 1: Soil wetting starts: after wetting the soil from the bottom the vapor content of the soil under the bricks starts rising (black line).
- Phase 2: Vapor rises in 1st row of bricks : vapors migrate from the soil into the 1st brick (dark blue), making its moisture content rise, initially slowly then much faster.
- Phase 3: Liquid moisture in 1st row of bricks (saturation): the capillaries of the first brick become saturated with water vapors and around 99% RH a transition between vapor and liquid phases occurs. This phase change is very nicely shown by another parameter we captured, the spontaneous wall potential (red line), which sharply drops from about +200 mV to -50 mV. Why this happens? In a nutshell: water vapors are positive, liquid water is negative. A change of sign of the voltage indicates a transition from vapor to liquid phase, an ongoing wetting of the masonry.
- Phase 4: Vapor rises in 2nd row of bricks : water vapors start migrating through the 1st mortar course and into the 2nd row of brick. The moisture content of the mortar course (grey line) and the 2nd row of bricks (light blue line) starts rising.
- Phase 5: Saturation 1st mortar course: moisture migration in the 1st mortar course speeds up (grey line), while the moisture content of the 2nd row of bricks also increases steadily.
This experiment shows the step-by-step upward migration of moisture: from the soil through the 1st row of bricks, 1st mortar course, 2nd row of bricks and so on. The pattern is obvious and it all occurs on its own, without any additional moisture source or mechanism being present – no water leaks, no moisture barriers or cement, no condensation, nothing at all. Soil evaporation is a standalone, self-sufficient wetting mechanism; its accumulation leading on its own to rising damp.
This lab experiment detailing the rise of moisture in “slow motion” in a controlled environment only captures the beginning of the process. But it is not difficult to imagine that if a wall is subject to the presence of soil moisture 24/7 for several years, decades or even centuries, a significant amount of moisture can accumulate inside the fabric – initially as vapors, gradually leading to liquid moisture transport. Once liquid water is present, even as a thin liquid film on the capillary walls, salts migration starts into the wall fabric, leading to salt crystallization and subsequent plaster damage - the combination of moisture and salts gradually developing the typical signs of rising damp.
Modern Academic Standpoint
Rising damp and its accompanying phenomena has been described by many technical research papers from all over the world, highlighting some of the irreversible damages it can create to old buildings.
Click on each publication to expand additional details.
Old-House Journal is a USA magazine devoted to restoring and preserving old houses. Since its establishment in 1973, the magazine has published many articles on rising damp, the 1994 May-June edition being one of the more comprehensive ones, covering its mechanism, its manifestations and most common remedies to overcome it.
The Journal says:
"Rising damp is most common in low-lying, high-watertable coastal regions such as Charleston, South Carolina, Galveston, Texas and New Orleans - the proverbial land of rising damp. (...)
The symptoms caused by rising damp have been recognized for centuries, and its general action has been understood for close to 150 years. (...) In the "Architecture of Country Houses" (1850) A. J. Downing how foundation walls laid with lime mortar absorb moisture from the soil, particularly damp soil."
Rising damp: capillary rise dynamics in walls, 2007
This UK research paper published by the Royal Society in 2007 not only acknowledges the existence of rising damp, saying that it is an important cause of wetness in buildings...
...but also discusses in detail the various factors influencing rising damp. The paper provides the necessary formulas for calculating various rising damp parameters (rising damp height, quantity of water inside the walls etc.) for walls of different thickness.
An operative protocol for reliable measurements of moisture in porous materials of ancient buildings, 2006
This scientific paper published by the University of Bologna, Italy in 2005, states at the very beginning that capillary rising damp (along with other types of moisture) is one of the main problems in old buildings.
The paper discusses the various moisture measurement methods, while also presenting a methodology on how to easily recreate rising damp under laboratory conditions.
Treatment of rising damp in historical buildings
This paper is part of a series of research papers on rising damp published by a research team at the University of Porto, who have analyzed in detail the mechanics of rising damp, the effect of various wall structures and finishes, and they proposed and analyzed in lab and in-situ a new wall-base ventilation system, as a means to reduce the effects of rising damp.
"Humidity is one of the main causes of decay in buildings, particularly rising damp. (...)
In historical buildings, rising damp is particularly difficult to treat due to the thickness and heterogeneity of the walls.
Traditional methods have proved somewhat ineffective. There is therefore a need to study new systems."
Rising damp has also been reproduced and studied under lab conditions.
Rising moisture, salts and electrokinetic effects in ancient masonries: from laboratory testing to on-site monitoring, 2013
This research paper on rising damp from 2013 studies rising damp and its effects under both laboratory conditions and in real buildings. The paper acknowledges that rising damp is a complex phenomenon influenced by a multitude of factors, which leads to the decay of both ancient and modern building materials.
Results of rising damp recreated in the laboratory after 6 months are also presented.
Building Dehydration - From Basics to Practical Applications, 2017
This 270-page Austrian technical reference book discusses in great detail every aspect of moisture movement and building Physics.
It describes in detail the development of rising damp through its various phases; one interim phase being interstitial condensation. The book makes a clear distinction between rising damp and condensation, which are two different phenomena.
The stages of dehydration and various mechanisms that contribute to the dehydration of the building fabric are also presented in a logical and structured way.
Rising damp in two traditional clay-brick masonry walls and influence on heat transfer performance, 2019
his 2019 research paper from China studied the effect of rising damp on the heat loss of the building and they found that "the presence of capillary water has a direct impact on the heat transfer coefficient of the wall." - the damper the walls the more heat loss occurs.
- Rising damp has been thought to be capillary action - liquid water rising inside the capillaries. As a result by eliminating the presence of liquid moisture (drainage) and by keeping the fabric breathable (e.g. lime pointing and rendering etc.) has been thought to solve the problem. This is not the case.
- Rising damp does exist as vapors always rise as part of the natural water cycle. Rising damp is caused by vapor evaporation from under the building into the porous building fabric as a result of natural soil evaporation.
- The wetting of brickwork from soil evaporation is a standalone, self-sufficient mechanism that alone can create rising damp over time, without needing any additional moisture sources.