Rising damp can be a major concern because of the damages it causes to old buildings worldwide.
Despite its name focusing on "dampness", rising damp is far from being "just" a dampness problem. Rising damp differs significantly from other dampness problems because of the presence of salts. Unlike rainwater ingress and condensation, which are “just” dampness problems, rising damp is a dual problem of dampness and salts.
Water alone rarely causes damages to a breathable masonry. A damp masonry, in the absence of salts, can undergo thousands of wetting-drying cycles and stay perfectly intact.
Between the two – water and salts – the crumbling of masonry caused by the salts is probably the most aggravating problem of rising damp. The role of water is often less obvious as it operates invisibly in the background, diligently transporting dissolved salts, indirectly contributing to the decay problem.
Solving rising damp involves the following two steps:
The primary role of a damp proof course (DPC) is to form a liquid water and vapour barrier.
A damp proof course can be created by physical, chemical or electromagnetic means. Several damp proof course technologies exist. These all differ in implementation, efficiency and longevity.
The technology of damp proof courses has constantly evolved. Each DPC technology was a natural evolution over its predecessors, attempting to improve and simplify the application process, while also addressing some of the shortcomings of previous generations. Here is a short development timeline and summary of each.
Based on written historic records, original physical DPCs date back to around the 1840s, possibly earlier. They were the first attempt to prevent rising damp during times when buildings were generally erected on the soil. Without a DPC a few decades or centuries later rising damp would have appeared causing fabric decay, high humidity and health issues.
The most common materials used for damp proof courses in the Victorian age were slate bedded in cement, hot asphalt, sheets of lead, glazed bricks and vitrified stone-ware tiles.
As we already know today, these "original" damp proof courses lasted anywhere from a few decades to about a century, eventually failing as they aged, as the lifetime of a damp proof course is shorter than the life expectancy of a building.
Here are some examples of damaged or broken down damp proof courses.
In the vast majority of cases one won't be able to assess the condition of a DPC by visual inspection, as 95% of it is hidden inside the wall. Instead, assessing the condition of the wall and plaster above the DPC level can give one indication about the condition of the underlying DPC.
As a rule of thumb: if the wall shows signs of rising damp above the DPC line, especially on sheltered internal walls, with no other moisture sources present, then the damp proof course is likely to be compromised.
Technical solutions had to be found to retrofit old buildings with new DPCs in order to keep rising damp in check.
The first attempt to repair aged, decayed DPCs that reached the end of their life, was to add impervious (e.g. blue engineering) bricks to the base of the walls, or to cut the walls with a large chainsaw and drive stainless steel plates into the cut - a very invasive and labour intensive task.
Technical advancements in chemistry made the retrofitting process of damp proof courses simpler and less invasive by injecting waterproof chemicals into the walls. This reduced the workmanship to a few drilled holes every few inches. Nevertheless, the injection process was still fairly invasive, leaving permanent blemishes on buildings, while giving variable results, performing poorly on thick solid walls with rubble filled core.
Further technical research into molecular phenomena and a better understanding of electrokinetic phenomena made possible a newer, smarter, less invasive approach to solve rising damp, by applying a small voltage to the walls through embedded wires.
But it was not all perfect, the main reasons why electro-osmotic DPCs failed over time were the corrosion or physical damage to the wires (as shown above), and more importantly, more recent findings have shown that in high salinity environments (e.g. old, porous, salt-laden walls) electro-chemical effects in the masonry rendered many of these systems ineffective.
Magnetic DPCs attempted to address the shortcomings of electroosmotic DPCs. New discoveries about Earth's energetic background and how these effect old walls, as well as advancement in wireless technologies resulted in the elimination of the trouble-prone wires - providing a contactless, non-invasive and hassle-free solution to rising damp.
A magnetic DPC unit that looks like a small lampshade and it can cover the whole building, You can read more about the Magnetic DPC technology here.
After the installation of a damp proof course, replastering is the second major phase in the handling of rising damp.
The main challenge in replastering after rising damp is the presence of SALTS.
Walls affected by rising damp often contain a significant amount of ground salts. These salts have been drawn up by rising damp and deposited into the wall fabric over many decades or centuries. When salts crystallize, they expand in volume 5-10 times, leading to the breakdown of the wall fabric. Crumbling, flaking and loss of building fabric are primarily caused by salts, not water.
Because air lime plasters have poor resistance to salts, modern damp proofing customarily uses sand-and-cement plasters which is not compatible with the fabric of old buildings.
Before going into technical details, it's worth mentioning that some conservation professionals don't think a DPC is needed as part of the rising damp solution. The main reasons behind this are:
Summing it all up: invasiveness, limited efficiency followed by non-breathable replastering - understandably - make chemical DPCs an extremely non-desirable proposition in the field of building conservation. As a result solving rising dampness is taken in the direction of improved breathability and lime replastering. This is definitely a good approach that works well for lighter cases of rising damp. However, for more serious cases it becomes less efficient - for a number of technical reasons discussed next.
In our practical experience, rising damp cases can be divided into several stages of severity:
The above categorization is just a generic guideline as there are always exceptions to the rule due to the many variables of the problem. There are, however, several aggravating factors, that can increase the severity of rising damp in buildings. These are:
Based on the above, for the conservation-friendly resolution of rising damp one can have several options. One should choose the solution one feels most comfortable with.
In line with current conservation policies, one can can replaster the walls with a common air lime plaster. This tends to work best in relatively newer buildings with low levels of rising damp. This type of plaster is also called sacrificial plaster, which means that the plaster is expected to crumble off and last only a limited time, requiring re-plastering every few years.
Here is a typical case of replastering with sacrificial lime: a 400 year-old stone building. The salts carried into the building fabric by rising damp have destroyed the lime plastering in a short 4 years, as shown below. Therefore, this type of lime plastering has to be repeated every few years.
As sacrificial lime plasters require ongoing replastering every few years due to the presence of salts, eliminating the problem of salts can increase the longevity of replastering significantly (about 10 times) without any downsides or negatives. This can be achieved by applying a salt-resistant lime base coat under the main lime coat protecting that from early decay.
This technology originates from ancient Rome. The Roman engineers have developed special lime plasters for damp environments. Mixing the lime with volcanic sands and ashes (natural pozzolans) results in lime plasters that can withstand very high humidity and salinity. These lime plasters (also referred to as water limes in old textbooks) have been used for centuries in very damp environments such as Venice. Applying this Roman plaster (Rinzaffo MGN) under the main lime coat would act as a breathable salt filter, protecting the plastering from excess humidity and the destructive effect of salts. The salt-resistant Roman base coat does not affect the breathability of the fabric, being itself a breathable lime plaster. The video below demonstrates the use of this lime plaster.
Although good quality breathable plastering systems can provide a dry, presentable surface for a long time, the moisture and salt accumulation in the masonry continues in the background behind the plaster. This aspect can be addressed by the non-invasive magnetic DPC system, an alternative to more invasive DPC solutions. This is the latest damp proof course technology that deals with rising damp by improving the breathability of the wall fabric. The magnetic DPC system can alone reduce the moisture content of the wall fabric, establishing a new, lower moisture equilibrium state in the walls.
This solution complements the replastering, reducing the moisture content inside the wall fabric which lime replastering can not address. From technical point of view, combining lime replastering with the magnetic DPC is the best overall solution.
The recommended lime plastering schedule, that "ticks all boxes" - breathability, long life expectancy, high water and salt resistance, moisture control - consists of the application of the following 3 plaster coats:
This concept is very similar to the current lime renovation concept, except it extends that by adding the Roman waterproof, salt-resistant base coat to the plastering schedule. This Roman coat does the "heavy lifting" in the background, protecting the other lime coats (the main and finishing coats) from premature decay from the combined effect of humidity and salts. Being a heritage-friendly material, it is extensively used in one of the most historic cities of the world - Venice - a World Heritage Site.
The renovation concept is detailed below.
Regardless of the chosen solution, in old buildings only a breathable approach should be taken when dealing with rising damp.
Modern non-breathable materials and solutions create long-term side effects, causing future - sometimes severe - dampness problems. Thus the use of cement platers, tanking and plastic membranes are considered non-building friendly solutions and as such these should be avoided in older buildings pre-dating the 1940s.
Today, virtually any renovation solution has breathable lime-based alternatives which do not have long-term shortcomings, are sympathetic to old buildings and restore the fabric's breathability making old buildings function as they were intended.
Here are the typical recommended materials / products for this solution. Other plaster variations are possible as we have different types of main coats (normal or thermal) and finishes (smoother, grainier, coloured etc.) depending on your needs or application. Please get in touch to discuss additional options.
Here are some of our projects using this solution:
This solution has won / been nominated for the following industry awards:
Here are some related pages with additional technical information, giving you a more in-depth understanding of this topic.
Here are some photos demonstrating this solution. Click on any image to open the photo gallery.
1600s timber-frame listed farmhouse undergoing full refurbishment from top to bottom addressing sympathetically many problems including: new roof, lime pointing, timber infill panels, thermal insulation, replastering, structural reinforcement with lime and lime floors – just to name the most important aspects of the project.
Here are some photos of disintegrated, broken down original slate DPC which have been frequently installed in old buildings in the Victorian period – a means to prevent and combat rising damp.
Here are some videos related to this solution. Please unmute the videos when playing them.
If you have any questions about a project, a problem, a solution, or any of our plasters - please get in touch.
We understand that each project is unique. Using the contact form below feel free to ask us any questions. Give us as much detail as you can about your project so we can get back to you with more relevant answers.
Here are some client testimonials:
We were recommended Core Conservation by some conservation professionals.
Following an initial consultation with an engineer, we installed the dehydration system into our Grade II listed Tudor cottage in October 2017. The Engineer returned only last week to evaluate changes to the severity of the rising damp in our walls since installation. After only 6 months there is a marked improvement in readings, some of which are 50% lower than those established at outset. We are very pleased with the findings and look forward to the next scheduled visit in 6 months’ time to learn of further improvement readings. Well done!
Here are some key application points about the application of each plaster, as well as links to the full application guides. Additional documents can be found on the individual plaster pages.
The plaster application video below explains the concept in detail.
