Cladding denseblock with travertine

I've just managed to pick up a load of travertine that I will use for a patio. I'm also going to build some raised planters out of denseblock and had planned to render them. However, I'll have enought stone left to clad them and use as coping.

The stone is 3cm thick. Can I simply use a standard mortar mix to stick them on and can anyone see any problems with this?

you will be better using a tile adhesive for the vertical faces, it will be stronger

Definately use a good quality powdered tile adhesive suitable for natural stone and for large tiles cause that stuff is heavy.