I had the brother in law install some Armstrong Alterna tiles in my basement bathroom this weekend. I provided an underlayment type material that the store suggested which would allow me to pull up everything if I ever wanted to change the tile. This material seemed to be just a very thick paper type material and did not act as a vapor barrier.
He laid the material down on the concrete floor and then used the adhesive to install the tiles. After looking at the job, I noticed that a control joint goes underneath the area and that it falls directly underneath the middle of a tile row (not the grout joint). I'm wondering if this is going to be an issue since the underlayment is free floating over the concrete. I had not filled the control joint with anything such as backer rod and sealant.