There are genuine applications where liquid water has to be kept out of certain areas and waterproofing old walls becomes a necessity. However, old buildings also need to breathe, which can appear a contradictory requirement to waterproofing old walls. Let's explore this topic in more detail. Â
Water ingress can take many forms, the most important ones being:
In such cases, due to their properties, regular lime plasters do not provide a robust enough, long-lasting solution. As a result, waterproofing jobs on old buildings are often performed with modern materials such as tanking slurries, bituminous tanking materials, plastic membranes, just to name a few. Although these perform well in keeping liquid water out, when used in older or listed buildings designed to breathe, they also come with important drawbacks or trade-offs.Â
Modern waterproofing materials have been designed in line with modern building philosophy: keep all moisture out. As a result modern waterproofing materials are completely waterproof, stopping both liquid water and water vapours. Although this is a desirable behaviour in many applications, in older buildings this behaviour is not ideal.
Unlike newer buildings, older buildings have been designed to be vapour permeable (breathable). By design, a well maintained fabric stops liquid water penetration but allows vapour waters to penetrate. This way the wall can regulate its own moisture content and keep the fabric dry (within limits).Â
Modern waterproofing materials being non-vapour-permeable (non-breathable), by blocking the movement of vapours, they permanently change the moisture dynamics of old walls, resulting in some very undesirable consequences long term.
Here are some of the most notable drawbacks of modern waterproofing materials when used in damp old buildings:
So the ideal waterproofing solution for old buildings would be some selectively waterproof material that can stop liquid water while allowing water vapours to pass. In other words, it should be waterproof and breathable at the same time.Â
These requirements, at first glance, seem to be contradictory - however the Romans figured out a simple, workable solution that just does that, the solution also being very building-friendly.
By adding volcanic sands and ashes (natural pozzolans) to the lime, the Romans have developed a wide range of lime plasters for a very wide range of applications - including many waterproofing applications which today are solved with modern Portland cement. Some of these Roman lime plasters were able to set underwater, being suitable for very damp environments. The longevity of these plasters was also outstanding, many of them lasting for centuries.
How can a lime plaster be waterproof and breathable at the same time? Modern research2Arizzi, A. & Cultrone, G. Aerial lime-based mortars blended with a pozzolanic additive and different admixtures: A mineralogical, textural and physical-mechanical study. Constr. Build. Mater. 31, 135–143 (2012). https://doi.org/10.1016/j.conbuildmat.2011.12.069 gave us a better understanding on how these plasters work. It all has to do with the pore structure of the material.
Normal lime plasters are macroporous, which means they have relatively large pores. Looking at their pore size distribution, most pores in air-limes are between 0.1 to 1.0 μm, with some larger pores in the 5 to 50 μm range.3 Santos, A. R. L. dos, Veiga, M. do R. da S., Silva, A. M. dos S. & Brito, J. M. C. L. de. Tensile bond strength of lime-based mortars: The role of the microstructure on their performance assessed by a new non-standard test method. J. Build. Eng. 29, 101136 (2020). https://doi.org/10.1016/j.jobe.2019.101136
Liquid water can only circulate through pores larger than 0.2 μm in diameter. Water can't penetrate pores smaller than 0.2 μm. Due to their pore distribution, normal lime plasters allow the passage of both liquid water and vapours.
The addition of volcanic ingredients to lime, depending on the type and quantity of volcanic materials mixed, can change the pore size of lime plasters. The right mix and quantity of volcanic ingredients can reduce the pore size under the critical 0.2 μm threshold, making some of these lime plasters completely waterproof while retaining their breathability.
Thus Rinzaffo MGN is an open-pore microporous (small pore) lime plaster that acts as a breathable water and salt filter. Its small pores stop liquid water. Its open pore structure allows the wall fabric to breathe. Its small open pores are impervious to salt penetration and crystallization, being free of crumbling and decay. This results in an extremely long service life of this plaster (several decades) even in very damp and demanding environments (e.g. basements), lasting much longer than any NHL plaster or other waterproofing, dehumidifying or restoration plasters operating on other principles.
The practical waterproofing of old walls with lime that "ticks all boxes" - breathability, water and salt resistance, moisture control, long life expectancy - consists of the application of the following 3 plaster coats:
The recommended materials are listed below. This concept can replace modern non-breathable waterproofing and tanking materials, being a listed building and heritage-friendly solution, that keeps old buildings breathable. Â
For more information, please see below a list of technical pages, projects, image galleries and videos related to this solution.
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:
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.
Waterproofing the service area of an old crypt with traditional Roman lime waterproofing and Cocciopesto plasters. On some parts of the room the MGN Lime-Pozzolanic Tanking Slurry System has also been applied to reinforce the waterproofing in critical areas.
This old cottage has been extended a few years ago, receiving a new extension. During flooding the waterproofing of the newbuilt extension did not hold, resulting in the flooding of the building. Using the Roman lime materials the waterproofing has been reinforced, preventing future flooding.Â
This old farm house has been converted to living accommodation and thermally insulated using Roman lime materials in a sympathetic way.
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.Â
Here are some client testimonials:
I agree, I can see with my own eyes how the Rinzaffo is dealing with moisture. I’m actually amazed by the product. It’s a difficult product to work with initially, but we have to understand that this is not the finish. I have seen with my own eyes how it is dealing with moisture. There are a couple of walls that I can see need 3 or 4 mm extra.
To breathably tank a building like Romford farm is unknown. I must admit I was dubious at the start, but open to the idea. There is no modern building products that I am aware of, or am used to that could possibly be an alternative.
I can see with my own eyes and other senses how the dampness in that building is disappearing the more work that we do. … You have to understand …. I entered that building early on…. It was rotten with moisture. I would say inhabitable. Day by day it gets better.
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.Â
The plaster application video below explains the concept in detail.
