High water table occurs when the level of groundwater rises to or near the surface, saturating the upper soil layers. The water table represents the upper surface of the soil, where the pores and fractures of the ground are filled with groundwater. This occurs due to excessive water accumulation beneath the ground, often from heavy rainfall or water seeping down from higher elevations into the surrounding soil.Â
Old buildings, especially those constructed before the 1870s, often lack a damp proof course (DPC). A DPC prevents dampness from rising up the walls. When there’s no DPC, the bottom of the wall is directly connected to the water table, which acts as an unlimited water supply.
Here’s how high water table affects old buildings:
Rising damp: the height of the water table plays a crucial role in the development and intensity of rising damp. Without a DPC, moisture from the water table can rise through the walls. Evaporation creates a pressure difference, drawing up more moisture and salts from the ground. This ongoing water intake leads to rising damp within the walls.
Masonry damage: high water tables mobilize soluble salts within the masonry which are carried up by rising damp into the wall fabric. These salts harm the building fabric, leading to deterioration. Additionally, a damp masonry can be subject to more frost damage, affecting the long-term integrity of walls, plastering and other structures.
Structural problems: the constant presence of moisture weakens building materials, affecting their integrity over time. Foundations, walls, and floors may suffer structural damage due to the saturated soil. Settlement issues, uneven settling, and compromised stability can occur on buildings situated on a high water table.Â
Reduced thermal efficiency: dampness in the wall fabric reduces the thermal efficiency of the building. Cold, damp walls are less effective at retaining heat, leading to radiating cold, discomfort for the occupants, unhealthy environment and potentially higher energy costs.
Health risks: mould growth due to damp conditions can pose health risks to occupants, especially those with respiratory issues.
In summary, a high water table can create significant challenges for old and listed buildings, impacting their condition, stability, longevity and habitability.
All the above problems can be addressed in a conservation-friendly sympathetic way, using building-friendly technologies and breathable, traditional materials. For starters, good drainage is essential to channel away as much liquid moisture away from the property as possible. However, most of the times a combination of various solutions are needed in order to tackle several problems caused by high water table.
Rising damp: a non-invasive damp proof course alternative to invasive chemical DPCs is the magnetic DPC. Instead of blocking the ascent of water by physical or chemical means, a magnetic DPC takes a completely different approach: it increases the breathability of the wall fabric by decreasing the adhesion forces between the water molecules and capillaries, allowing moisture to evaporate much easier.Â
Masonry damages: hydrated lime (air-lime) plasters do not perform very well in the presence of high humidity and salts. Although very breathable, sustained humidity and salts decrease the longevity of lime plastering significantly, leading to frequent replastering and increased maintenance costs. A conservation-friendly much longer-lasting alternative is replastering the walls with the Roman lime plastering system.
Reduced thermal efficiency: to improve the thermal efficiency of old buildings in a building-friendly way, we have high-performance lime thermal insulation plasters, with or without aerogel. Low U-values of 0.5 or lower can be achieved with only a few centimetres of breathable lime thermal insulation. More information on the lime thermal insulation page.
Health risks: lime is a very healthy material that is naturally anti-bacterial. Some lime plasters such as Cocciopesto (a traditional Roman mix of lime and brick dust) or lime-hemp or lime-clay plasters are excellent humidity regulator creating a healthy, low-humidity environment.  Â
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.
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
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 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.