Introduction
Rising damp is a commonly misdiagnosed issue in existing buildings, often leading to unnecessary and costly treatments. The misdiagnosis is primarily a result of the incorrect interpretation of visual evidence and moisture meter readings. Specialist remedial contractors promoting injected ‘chemical damp-proof courses’ have played a significant role in associating rising damp with the absence of such treatments. While this misdiagnosis has benefited their business, it has led to the destruction of original plasters and finishes, unnecessary damage to structures, and wasteful expenditure of clients’ resources. This article explores the true causes and effects of rising damp and presents alternative cost-effective solutions for managing damp problems in buildings.
Understanding Rising Damp
Rising damp refers to the upward movement of moisture through permeable building materials via capillary action. It becomes problematic when the moisture penetrates vulnerable materials or finishes, particularly in occupied areas of a building. This moisture carries soluble salts from the building materials and its source, resulting in the formation of deposits and efflorescence. While the presence of a distinctive ‘tide mark’ is often associated with rising damp, these salt accumulations can persist even after the original water penetration has ceased. It is important to recognize that water penetration can occur from various sources, not just rising damp.
Common Sources of Moisture
The primary source of moisture at the base of walls in buildings is often defective ground and surface drainage. Factors such as rising ground levels, failed drainage systems, and inadequate consideration of drainage slopes contribute to this issue in almost every building. Chronic plumbing leaks or flooding from plumbing or drainage defects can also lead to the accumulation of moisture reservoirs in the foundations. Additionally, damp conditions at the base of walls can be exacerbated by condensation, particularly when warm, moisture-laden air cools against cold surfaces due to reduced insulation caused by water penetration.
Problems Caused by Damp Masonry
Damp masonry at the base of walls can give rise to several issues. The moisture content of the structure may rise to a level conducive to the growth of decay organisms or adversely affect the materials themselves. Inorganic materials can lose their structural strength in very damp conditions, and the growth of moulds on surfaces and within porous materials becomes a significant aesthetic and health concern. Furthermore, the deposition of soluble salts on the surface or within the pores of materials can cause aesthetic and structural damage.
Cost-Effective Treatment Options
Addressing high moisture levels in the base of walls requires proper identification of the moisture source and the defect responsible. The most cost-effective solutions depend on accurately diagnosing the problem. Some treatment options include:
Suitable moisture sinks and repair of contributing defects: Providing moisture sinks at the source and repairing broken pipes or other defects acting as moisture sources.
Physical barriers and isolation of vulnerable materials: Introducing physical barriers such as damp-proof membranes or hydrophobic materials to form a damp-proof course and isolating vulnerable materials from damp fabric.
Surface water drainage: Minimising moisture sources by improving ground drainage and re-detailing surface drainage to ensure water is drained away from the base of walls.
Wall construction considerations: Avoiding impermeable finishes around the base of external walls and using breathable lime mortar renders instead. Cavity wall construction, when properly ventilated, can also help dissipate moisture.
Ventilation: Re-establishing ventilation in sub-floor cavities, basements, or cellars to prevent moisture build-up and subsequent penetration into vulnerable structures. Through-ventilated suspended floors are often preferable to impermeable concrete slabs.
Conclusion
Rising damp is frequently misdiagnosed in existing buildings, leading to unnecessary and costly treatments. When we carry out a damp survey a more logical and astute approach is taken to diagnosing damp problems in buildings which more often than not, results in no recommendations for chemical damp proofing.
