So, we have to go back to stone-age to improve our indoor air quality? Not really. We may have to just revisit some of our conventional building techniques with an open mind and blend it with modern technology.
Perhaps clay plastering of wall may be the simplest and the easiest solution to the most dangerous problem of poor indoor air quality faced in Indian homes. In fact, it is feared that indoor air quality is much worse than the outdoor ones though not much studies have been done in this direction.
Now a days experts are advising clay plasters because of some of their functional qualities like breathability and ability to regulate relative humidity. Most of the houses in congested cities where space is the biggest constraint face the problem of airtightness leading to poor air quality inside homes. Due to the airtightness there will not be any scope for moisture created by the people residing within the house, kitchen, bathroom, etc. to find a way out. Impermeable walls are much more prone to transient episodes of condensation caused by cooking and washing, or simply by the breathing of a large gathering. Insects also thrive where liquid water is available. However, clay plastered wall can solve this problem due to its breathability quality. Unfired clay can absorb and desorb indoor humidity faster than any other building material. Studies show that clay plasters can regulate relative interior humidity between 40% and 70%.
Different methods are used for preparing clay for plastering in different parts of the country. For example, in Kerala, soil, sand, and lime is added in certain proportion and carefully mixed in the dry state to which enough water is added to create stiff mortar. Usually such mix is cured for a few days before it is used to enhance its elasticity. There is a practice to add rice husk and cow urine before using it for plastering. In some parts of the coastal Karnataka jaggery is added. Once the mix becomes ready for use, plastering can be done normal way. Usually, plastering is done in 12 mm thickness.
Here is a construction practice which was followed in ancient India but ignored in modern times which can make you breathe easy!