I would think that an adhesive made for masonry in your area would work OK. Also there are many types of mortar that are successful in joining and not cracking. I would carefully and completely fill the joints and smooth the exposed seams so that water could not enter/gather and freeze. You may want to try a combo with mortar providing the main bond and, after curing, covering the exposed areas with waterproof adhesive.

Why do you want to join the stones? Why not do dry rock formations?

I am leaning towards dry rocks, but joining might help make taller - odd shapes.

hi why not use expaning foam..here in minnesota its called 'great stuff' its used to fill cracks and hole to insulate. I use it in my pond outside to hold rocks and things in place..its yellow in color, but after it is dry you can paint it..works great....linda

I visited the Dr. Sun Yat-Sen garden in Vancouver, Canada a few weeks ago. I was disappointed in some of the rock work. The limestone was imported from China and looks very exotic with all the holes in it. I'm no expert on placement of Chinese limestone, but even I can recognize when rocks are not right side up. Note rock in upper left of picture.
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