Here in n.c, we use 2 shovels masonry sand, one shovel Portland cement type I/II. No bonding agent is needed except for the Portland. I make what we call a slurry. I take a trowel of dry Portland, put in a bucket then add water till it's a paste. I lightly wet my stone then paint it with the paste before I set it in the bed joint. The glue that bonds..
