# What is Capillarity?
**Capillarity (or capillary action) is the physical phenomenon in which a liquid — usually water — is transported upward through fine openings, pores or channels in a material, against the force of gravity.** In construction, capillarity is a key concept because it is the main cause of rising damp in walls and structures.
## How Does Capillarity Work?
The phenomenon relies on the surface tension of water and the attraction between water and the material surface (adhesion):
– In narrow openings (capillaries), water is pulled upward by adhesion
– The narrower the opening, the higher the water can rise
– In brick, water can rise capillary more than one metre
– Concrete and natural stone also exhibit capillary action, depending on their porosity
## Capillarity in Building Practice
Capillary moisture uptake is a common cause of dampness problems:
– **Rising damp** — groundwater rises through the foundation and masonry into the wall
– **Damp stains and efflorescence** — visible as white deposits (salts) on the wall surface
– **Mould growth** — caused by prolonged high moisture content in the masonry and internal finishes
## Prevention and Solutions
– **Damp-proof course (DPC)** — a waterproof layer in the wall, just above ground level
– **Injection** — introducing a water-repellent agent into the masonry
– **Drainage** — channelling groundwater away from the foundation
– **Hydrophobic treatment** — making the outer surface water-repellent
## Related Terms
– Rising damp
– Damp-proof course
– Building physics
– Hydrophobic treatment
– Drainage
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