Building an outdoor staircase in natural stone and considering how the stones should be attached to each other. It is a small staircase with two steps that is 180 cm wide.
For the risers, I am using limestone blocks (about 11x30x20 cm hewn blocks), and for the treads, I am using sawn porphyry slabs (30 cm wide in varying lengths).
The challenge is that the limestone blocks are a bit uneven, and the porphyry slabs vary in thickness (30-40 mm).
The question is how I should attach the tread to the riser. I'm considering placing cement mortar A on the blocks and pressing down the tread (the sawn slabs). This would allow me to adjust the height so that the tread is completely even (about 4 slabs per step).
The advantage of cement mortar A is the price (compared to, for instance, Ardex 32) and its good consistency/ease of use. If it weren't so thin, fine concrete would have been an alternative.
Am I thinking wrongly, are there any risks with using cement mortar A?
