I have been looking into this extensively lately, I am in Thailand and want to visit Singapore and I wanted to fly back from SIN and the same day my flight returns to the UK, have been told by several sources as it’s on two separate tickets I cannot do it without applying for a Thaipass as I am not classed as a transit passenger
is a problem now I am sorry to say. You will need to apply for a Thai pass (double check as I am not sure if there are separate rules for Laos) or they won’t let you on the plane to Bangkok
But my understanding of you are on separate tickets you will have to pass through immigration and customs and to do that you need a Thaipass