Last year I had made a decorative frieze in the basket weave pattern, and one of this spring's jobs was to mortar it together. Doing it freehand wasn't at all successful, so I had an idea. I put the pieces upright in a frame the size I wanted:
I put dry type S mortar mix between the cracks about half way up, and sprayed it with water mist as i did:
A day later it had set up well, although it was sandy on the surface, from washing down the portland with the mist. I mortared it with conventionally mixed mortar. Here's the frieze setting in position before mortaring it in:
