[1990C4S]

I have laid a flagstone walkway from my porch to the road, gravel base and screening on top. That job is complete.

Now my cement porch ( 9' W x 4' D) looks bad in comparison, so I want to face it and cover the surface with flagstone.

I have lots of 1/2" flagstone rectangles, but I'm not sure what to use as mortar. This is a covered porch, but open sides. It will see snow, rain, and winter/summer temperature extremes (-30F to 95F).

I've read that a mixture of lime, sand, and Portland cement is good. Looking at mortar products, there is 'rapid set', and Quick-crete 'plain' and Type 'S' that all appear to be outdoor rated. I would prefer a premixed product, but only if it's not inferior to mixing my own.

There are also concrete bonding adhesives that I can use as a surface prep (and the back side of the flagstone?), but they can also be used as a mortar additive.

This is a job I want to do once, and do right...any suggestions?