Lime terracing was a popular method of roof treatment for ancient structures. Roofs of many buildings are witness of that technology. I remember a summer about 45 years back. That was a pleasant activity to me, which I have still kept in the jewel of my mind. Bankura district in West Bengal is very hot in summer. I grew up there in a single storey Govt. quarter of irrigation project. The staff quarter was newly built and had no top covering on brick bat, cement concrete roof. It was so hot to stay under the particular roof that the children used to suffer from fever. I too could not escape from this problem. One fine morning, I heard that SAONTAL TRIBAL women are coming to do something on the roof and our small house will turn to cold. That surprised me. I enjoyed the entire activities which I remember. The tribal women used to come every morning and sitting on opposite rows, started compacting red coloured mortar on roof in a fantastic rhythm with their tribal song. After few days, an engineer came to see the finished work. I climbed up on that nice red coloured finished surface. Someone was applying mastered oil on the finished surface. The engineer wearing a SOLA hat (Sola wood comes from a tapioca plant), took a betelnut and a hammer. One man placed the betelnut (SUPARI) on the finished surface and hammered on it to break repeatedly. After he broke it, the engineer looked on the surface where the betelnut was placed to break. He was happy to see that there was no impression left on the surface after hammering the betelnut repeatedly.
We stayed comfortably under that excellent insulated and waterproof roof till the date we left that quarter after my father’s retirement, when I left for USSR.
Now I can explain that technology in view of participation of microbes.
The main ingredients of that lime surki mix was small brick bats, surki (coarse part of broken clay bricks after screening), dense jaggery with adhesive property, METHI and water.
The first step of the methodology was fermentation of jaggery by bacteria.
Lactobacillus plantarum, Bacillus sp and Arthrobacter sp are the species of bacteria, which meet most of fermentation. It reduces the pH value; hence jaggery is converted to an acidic end product. When available sugar for microbial growth depleted, acid production decreased. The pH first decreased and then started to increase. The rise in pH in later stages was mainly due to the depletion of sugar for lactic acid production. The buffering capacity of the calcium from the shell solubilised into the media and nitrogenous compounds released by the proteolytic activity of the endogenous and microbial enzymes were also responsible for the increase in pH values of the protein liquor. The abovementioned bacteria are identified today for calcification and hardening of lime. Today those bacteria are used to prevent decay of marble stone monuments.
So, the use of microbes is not a new technology. Earlier people had no idea about microbes. But, they were aware of the function of microbes in fermentation. Today, these type of bacteria are sprayed to protect marble monuments from natural degradation.
In this section of Technology Coordination Technology Part-12, I would like to emphasis on the old traditional technology of roof insulation and waterproofing using modified methodology. Because of that, old technology has proved its durability, excellent thermal insulation and waterproofing property. Today, advanced polymer technology are not able to perform equally in terms of durability and cost-effectiveness. The materials which were used for the purpose were not friendly with parent concrete by nature. As a result, layers of polymer coating after placing insulation board could not perform in terms of durability.
But, red brick surki is not available today.
So, is it possible to recall that old technology to enjoy that comfort, durability with low cost? Researchers will certainly think on this subject today.
Before we start any research on this subject, we should try to choose natural ingredients. Our aim is to achieve the insulation property with waterproofing at low cost by calcification and hardening of lime. Accordingly, the ingredients should be selected carefully. We know how to incubate the colony of bacteria in modern technology. Still, we can choose the old method of fermentation. That takes 24-36 hours fermentation time. If we look back to the old roofs covered by lime terracing, we observe an effect of self-healing concrete. Many concrete roof cracks were sealed due to calcification of lime by bacteria. We will get that benefit in the modified technology based on that old methodology.
Intensive research work is available on microbes used for calcification and hardening of lime to prepare self-healing concrete. This is not at all a complicated subject if you look back to our old traditional technology. Most of my engineer friends are excited to know more about the microbial utilization for self-healing concrete. Many of them are worried about its cost. Because of the modern technology based on microbial culture and utilization in structure, it seems to be costly. Yes, it is. But, in our old traditional technology, those were not costly. The reason behind this is the advanced technological approach which includes lots of experiment, trials, study and research that were already done by our late technologists. Only we have to finish it using our available natural resources.
This work will help us establish a new modified method of low cost long term durable, waterproof with excellent insulation property. I hope the researchers on the related subject will think on this matter and be interested to share their ideas in TECHNOLOGY COORDINATION TECHNOLOGY PART-13. I would like to invite all technical professionals to share their valuable views to establish a new concept in the building industry, which is useful in the case of cost, quality and durability.
To be continued in Part XIII…