This is what I used:
http://www.homedepot.com/p/Loctite-PL375-28-fl-oz-Heavy-Duty-VOC-Construction-Adhesive-1390599/202020479#.UhMpPD9f1aQ
M.D. Holloway, If you want motar, you have to have at least 1/4" or 1/2" between the bricks. I want no gap, as you can see in the pic. Also, the surface where they meet is flat. I don't think motar will make it very strong.
VINMAN, I searched on "PL masonry adhesive" and found "Loctite PL Premium 28 fl. oz. Polyurethane Construction Adhesive". Similar to what I used, except it is premium instead of 375. Is that it?
john70t, I broke the join so the surface can be even, no gap.
wdfifteen, thanks.
Scott, nice bed scott. For me, it took a long time. I also built couple columns with the same type of brick. The one against the wall, I want to fill it with concrete and bars inside in case any drunk driver wants to test his car.
To those who recommended PL masonry adhesive, is this what you are talking about?
Loctite PL Premium 28 fl. oz. Polyurethane Construction Adhesive-1390594 at The Home Depot
Thanks all.