Cellars and lime
When it comes to cellar waterproofing, modern methods often involve tanking, a process where a waterproof coating is applied to the interior walls to prevent water penetration. These methods can create ongoing problems as they hide a symptom rather than dealing with the root of the problem.
Lime possesses natural breathability, allowing moisture in the form of water and vapour, to evaporate rather than becoming trapped within the walls. This is a crucial advantage in cellars where maintaining a balanced moisture level is essential to prevent issues like dampness and mould growth. Wet walls are cold walls which help create issues with condensation. Trapping moisture behind an impermeable coating has various disadvantages:
Breathability Issues: Historical buildings often rely on the natural breathability of their construction materials (like lime mortar) for moisture regulation. Tanking can trap moisture within the walls, leading to potential long-term damage such as dampness, mould growth, and structural decay.
Material Compatibility: The materials used in tanking may not be compatible with those used in historical buildings. Modern waterproofing materials can have different thermal and moisture properties compared to traditional materials, leading to potential stress and deterioration.
Structural Stress: Applying a waterproof layer can create a 'seal' that prevents the walls from naturally expelling moisture. This can increase the risk of trapped moisture exerting pressure on the structure, potentially leading to structural damage.
Alteration of Historical Fabric: Tanking can require significant alteration to the historical fabric of the building. This can impact its historical and architectural value and may not align with conservation ethics, which often prioritise preserving original materials and construction techniques.
Aesthetic Impact: In cases where tanking is applied to visible parts of a building, it can alter the appearance and character of the structure. This is particularly significant in historical buildings where aesthetics and authenticity are key considerations.
Maintenance and Repair Challenges: Once a tanking system is in place, it can be challenging and costly to maintain and repair, especially if it fails or if access to the tanked areas is restricted.
Limited Effectiveness Against Capillary Action: Tanking can be less effective against moisture rising through capillary action in old masonry, a common issue in historic buildings. Capillary moisture can bypass tanking systems, especially if they are not meticulously applied.
Potential for Concealing Problems: By masking the symptoms of dampness, tanking can sometimes conceal underlying issues, such as poor drainage or structural defects, leading to neglected maintenance and worsening of the original problem.
Regulatory and Permission Challenges: Making significant alterations to a listed or protected historical building, like tanking, is unlikely to be passed by a conservation officer.
Cost: Tanking, especially in large or complex historical buildings, can be a costly endeavour, not only in terms of initial installation but also in ongoing maintenance and potential remediation of issues caused by the tanking itself.
The question then becomes what happens when there isn't any tanking? As long as lime based materials are used, moisture the moisture can more to the surface. This is where effective ventilation takes over. For a cellar to be dry it requires constant low level background ventilation to remove damp air and allow for its replacement with warm and dry air. The moisture from the walls can then evaporate and the process continues. The use of lime is the only conservation option, it’s physically more flexible, deals with moisture effectively and is more environmentally friendly.
