My 2-part article on the purpose of Paavai nonbu and how it was done can be read in the following links.
http://www.tamilhindu.com/2010/01/paavai-nonbu-and-thai-neeraadal/
http://www.tamilhindu.com/2010/01/paavai-nonbu-and-thai-neeraadal-2/
The articles are in Tamil and those who can not read Tamil, can however browse this blog for my earlier articles on this topic.