Check out Epobond or Duracrete at email@example.com
. or here in Canada I used to sprinkle a product called seal bond where I was going to put mortar (that also had seal bond in the mixture) to start joining brick to concrete or stone. On the Internet there is information on making your own mortar which is stronger than the store bought mixtures. The store bought mixtures are good when fresh and properly stored.....it's just that YOU don't know how fresh or if it has been stored properly.
A case in point......I bought caulking from HomeDepot. It is cold up here and if Caulking freezes it's no good...comes out in chunks. I had bought a case and they refused to replace it because 'they' said it had been properly warehoused.....their warehouse is not heated.