After a bit of research I found 10 of the 12 grounmds for divorce in Thailand explained. It all comes from the Divorce Act (Thailand): Section 1516:What are the current grounds for divorce in Thailand?
Actually after posting my question I did some research on my own - apologies for not doing that in the first place! While I came up with some info, you've supplied me with a lot of detail I did not come across - especially on examples of 'desertion'.
Thanks very much - I appreciate that.