Terrace tile installation/connection: Use sand or gravel?

Hello everyone,

we are now ready and will build our terrace this summer. We have chosen a concrete slab: 60x30x4.5 | weight: approx. 18kg. Our garden landscaper has prepared the base (60-80cm compacted mineral mix) and there are still about 20-30 cm remaining up to the finished terrace floor level (depending on the slope). The installation instructions for the slab say "Installation note: joint spacing: 3-5 mm, base: sand bed or gravel/grit bed". Now my question is: which is more sensible? Sand or grit? What grain size? How are the joints then filled in each case?

The second question is: how do I create the connection to our house facade? We have a solid house with insulation and plaster. Is it sufficient to lay a strip of tar paper between the facade and the terrace slab, or should you leave 1-2 cm of air here and then fill it with sand / grit?

I would appreciate a few tips.

Best regards Sebastian

We have now decided on a gravel bed and will leave 1-2 cm of space towards the house, install roofing felt, and then fill with gravel. Does anyone have experience with joint sealing? There is supposedly something similar to sand, which is slurry-applied with water into the joints and then seals them so that nothing can settle and nothing grows...