"SteveB" wrote in message
news:YhbQd.96496$mt.47412@fed1read03...
I want to make some mortar to stick some pieces of flagstone to vertical
cinderblock surfaces, and to place them horizontally, too. The horizontal
would be capping, and laying on top of other pieces of flagstone.

What is a good recipe for mortar that will stick? Or should I just use
the premix stuff at Home Depot?

You may want premix thinset mortar, but I am not certain. That is what I
used to lay slate tiles onto backerboard for a woodstove hearth, but it was
an interior application. I also used a special additive - forgot the name -
that makes the mortar stand up in points, and flow less - better
consistency.