Heat-proof your house
Is your building equipped to handle those scorching rays of the sun? A. C. RAVI RANGASWAMI elaborates on the subject of thermal insulation.
WE ALL know that the temperature inside and outside a building is different. Heat is allowed to pass rapidly through some building materials but some other materials do not allow heat to pass. The term `thermal insulation' is used to indicate the techniques by which transmission of heat through the building is reduced.
Besides enormous savings in electricity cost, an external thermal insulation enhances in a significant way the comfort in a building, provides a healthier environment and helps in minimising damage to buildings.
The effectiveness of thermal insulation is directly proportional to the type of material and its thickness, measured in terms of thermal conductivity.
Thermal conductivity is the amount of heat in kilocalories that will flow through a given material in a given period of time. Thermal conductivity of a material depends on its density, porosity, moisture content and temperature.
The choice of the insulating material depends on the area to be covered and the cost of heating or cooling. There are various types of insulation materials (see table).
In the case of building protection, the following methods of thermal insulation are normally used:
Surkhi or brick bat coba
Surkhi is an artificial pozzolana made by powdering burnt bricks. In older times, in our old structures, a very special lime surkhi was used, which was successful, but it needed very skilled and experienced people.
In fact, they belonged to the families practising such crafts and we do not have that kind of trained craftsmen now.
Brick jelly concrete
While brick bat coba was common in the north of India, Brick Jelly Concrete, made with broken bricks, lime, kadukkai, jaggery and so on, was preferred in the south. Like the lime surkhi, this was also successful because of the sincere labour and plenty of time available.
But due to lack of quality labour, materials and paucity of time, this system is not successful.
The surkhi and brick jelly concrete were used to provide slopes on the flat terraces for easy draining of rainwater and also some sort of poor insulation.
In India, sometimes it is accepted as a standard waterproofing system. It is very common that the screen provided over the brick concrete cracks because of non-compatibility of surkhi / brick jelly concrete with cement. These cracks allow ingress of water, which travels through the brickbat (which is so porous) to the RCC slab. This whole process results in the failure of the waterproofing system and the slab starts leaking.
It is found that generally, bitumen felt is applied on roof surfaces, which have a failed surkhi or brick jelly concrete system.
Bitumen or bitumen felt is no solution as the bitumen tends to crack due to the oxidation/UV radiation in a couple of seasons and in fact worsens the situation.
The problems with thermocol are not very different from those in using surkhi / brick jelly concrete. In fact, once the water enters through thermocol, it starts absorbing water, ultimately rots and affects the reinforcement and the slab.
Vermiculite or perlite concrete roof decks
These products are lightweight materials and are good for thermal insulation. But these materials when used for roof decks do pose some problems. Since they are soft materials, they need to be covered by tiles or some other hard material to make the surface trafficable. Vermiculite is very porous and needs effective waterproofing.
The unusual insulating and corrosion-resistance properties of these products are excellent. The ceramic compound with a high quality acrylic binder provides elasticity and a strong adhesion. The reflective ability of the ceramic compound will reflect as much as 96 per cent of heat wave reaching the surface where applied, thus lowering the conductive transfer of radiant heat to the inside.
Experts are convinced that a typical thermal insulation product which is to be applied on the flat terrace must possess the following qualities: Other than providing good thermal insulation, it should be non-toxic, fire-resistant, have the ability to bond with almost any surface, act as a barrier against early water penetration, reflect harmful UV rays and be able to take durable, anti-skidding coatings as the final component.
A product has been developed based on these requirements. This product is a combination of lightweight materials along with redispersable polymer powders that works as a binding agent in cement-based dry mix mortar.
The mortar consists of cement, fillers, additives, admixtures and polymer binding agents. A few companies in the weatherproofing business are presently testing the product in India.
(The author is a Chennai-based weatherproofing consultant)
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