Brad, thanks for your encouragement and useful info. The only reason I thought to make grooves in the shingles was to replicate the natural grooves you get when you split the logs. I hadn't thought of the reactions due to cellular damage. Its a good point, especially because the humidity is so high here that mould or fungus could be a problem. Ive heard that the tannins in teak are a preventative, but you can't be too careful.
I decided not to try to split the logs because the local carpenters are not at all familiar with doing that, the logs are not that big, and the time it would take, I only have one froe. I can get them all rough sawn with a bandsaw in an afternoon.
Regarding coming to India and not wanting to go back. Thats what happened to me 30 years ago. I couldn't even think of going back now. I'm resigned to living the rest of my life here. There are so many problems in India, mostly in terms of efficiency. But the people, the atmosphere and the culture particularly in the rural areas are what keep me here.