What is meant by Capillary water in buildings?
Construction materials, like concrete, aggregates and sand, are porous and allows water molecules to rise due to capillary action. This creates a ring of dampness in base of buildings or structure including lateral walls due to accumulation of capillary water.
The principle behind the capillary rise is the surface tension (cohesive force) of water due to polarization of water molecules. It is also defined as the rise of water due to cohesive and adhesive force in between liquid and surface. This uplifted capillary water most often carries minerals or salts (sulphates, chlorides, ammonium compounds) from sub soil with in it and it react with building materials used for substructure or foundation, which may weaken the structure due to deterioration.
The capillary rise depends on the porosity of materials used for construction and types of soil. In different soil types height of capillary rise is different. In case of gravels, it is moderately less. Capillary water rise is different types of soils are given below:
Sand – 1 to 8 feet
Silt – 12 to 16 feet
Clay –12 to 20 feet
Effects of Capillary Water in Buildings
The capillary tubes are elongated narrow cavities with very small internal diameter. Capillary suction enables the porous materials (building materials) to take up the moisture against gravity to a long distance through it. Theoretically, it is found that the water can rise more than 10 meters in homogeneous materials.
The rise of dampness via capillary suction is quite slow. But as mentioned above the capillary rise can make serious issues in a building or structure. The rate capillary rise changes in according with seasonal changes. In rainy season the capillary rise is more compared to summers. The water molecules most probably carry salts or minerals within it (if the site is near to coastal areas) and that may react with the building materials and leads to strength loss in concrete and bricks and corrosion in reinforcement etc. The water often carries dissolved salts within it and it may accumulate on brick layer.
This crystalline white settlement of salts is called sub efflorescence which further damage the bricks and mortar and which is called spalling. The presence of water in brick layer or wall can weaken the mortar or plaster and causes deterioration. In case of exterior walls, the water may evaporate quickly. But later on it causes fading and creates unpleasant atmosphere inside the rooms.
In the case of concrete, the capillary rise can cause long term durability and strength issues. Most of the deterioration caused in concrete is because of the accumulation of salts from water. The salts (chlorides) can react with concrete and reinforcement inside in the presence of oxygen and the reactions with reinforcement trigger corrosion which will lead to expansion of reinforcement bars due to rusting.
The volume change in steel bars finally end up breaking concrete and damaging the steel bars too. In the case of foundation similar issues will happen if it is subjected to capillary rise. The rusted reinforcement bars gradually burst out reducing the concrete cover. Similarly, cracks develops on concrete and this will significantly affects the strength and durability of structure.
Remedial measures for capillary water in buildings
In old construction practices there were no much attention given to prevent dampness and other issues due to capillary rise in buildings. As technologies developed several methods are now available to prevent capillary rise in buildings. Some of them are listed below:
- Provide an impermeable barrier between soil and structure: It is the most effective and common method adopted to prevent capillary rise. Impermeable barriers such as plastic, bitumen, glazed bricks or other geo-textile fabrics are used in between building materials (foundation or wall) and ground soil.
- Integral damp proofing: This method focus on adding waterproofing materials to the concrete during casting to make the structure extremely impermeable to water.
- Replace the clayey soil by gravel layer: As mentioned above clayey soil is much welcoming to capillary rise. So providing a layer of gravel by replacing clayey or silt soil were the building materials comes contact to the ground prevents water penetration to the structures.
- Guniting: In this method an impermeable membrane is created on the surface of building material by applying high grade cement mix mortar. For that a special machine called cement gun is used.
- Provide wall base ventilation system: This method is used to clear off water which contains dissolved salts. A ventilation system with a channel which operated by hydro regulated mechanical device. When the moisture rises through the wall, it is get redirected to the ventilation and evaporated with air circulating inside the channel.
Conclusion
The capillary rise primarily depends on type of soil and porosity of materials. Capillary rise mechanism is far more important to be considered while designing a building.
As we know, the capillary rise can happen without hydrostatic pressure. So, it is very important to adopt preventive measure against capillary rise to maintain load carrying capacity and durability of structures. Historic or old buildings are most affected by capillary water. As on modern construction technologies developed, wide verities of methods are available to slow down and prevent capillary water in building foundation.