My 1 year non immigrant B expires at august 31. Because I have visitors from Europe I will accompany them to Mea Sai / Tachilek at August 19 and return the same day after we would like to stay for another ten days in the upper North.

For this trip I have a re entry permit stamp in my passport.

Because our trip is close to the expiration date of my visa will I get a 30 day or even 90 days stamp on the Mea Sai border ?? Does anyone know.

Are you here on a visa stay of 90 days or an extension of stay of one year? A re-entry permit only keeps your present permitted to stay stamp alive - so if now 31 August it will allow the 31 August stamp on your return.

If you have a multi entry visa that is valid until 31 August your new return before that date would get a new 90 day stamp with no need for a re-entry permit. But if your visa has already expired (more than one year from issue date) and the 31 August is really your permitted to stay date the re-entry will keep that alive - or you could obtain a 30 day visa exempt entry without it.