@Cla***
It is your use of wrong terminology that's messing up the answers to your question(s)..
As people correctly stated there is NO such thing as a 30 day visa on arrival :/
There is however a 30 day visa exempt entry :) which people from 51 countries (ireland included) get when they enter thailand without having bought a visa from a thai consulate before hand.
You are limited to TWO 30 day visa exempt entries per year by land.
Also be advised those southern land border crossing officers can be finicky and ask to see 20K baht in cash.