Hello all experts! I am planning to build a small entrance step in stone. From the ground to the door, it is 25 cm, and I'm thinking of a step at 15 cm. I am considering using Leca blocks, which are 9 cm high, for the frame, gluing them together. Then I plan to attach paving stones around the blocks like a frame and stones on top. I will attach the stones to the Leca blocks with flex-fix for outdoor use. Any objections from the gathered experts?
I would have laid the first layer of leca with mortar against the concrete slabs, but even better would be to remove the concrete slabs and pour a "foundation" for the stairs; otherwise, I would say your plan works...
Flexfix is primarily for tiles and on solid constructions, so I wouldn't choose it. For Leca against Leca, you can use stone adhesive if you want, it’s quick and easy, but I usually use mortar (there is a "thin joint mortar" which is good if you have stones without recesses for reinforcement.)
I would use mortar, but stone adhesive should also work. One thing you should consider is that water can drain away so that the leca blocks don't stay soaking wet in the fall and can freeze and crack or knock the paving stone loose later...
