Laying terrace slabs - Substrate in the conservatory?

Hello everyone,

about 10 years ago we built a house and had a normal terrace (with granite slabs) installed. Now we want to replace the granite slabs with terrace slabs (wood look) measuring 120x40x2cm.

A year ago we converted the terrace into a cold winter garden, meaning that rain or a slope (which we also don’t have now) is not a problem.

I have now checked the subsoil and found the following:
- the first six centimeters consist of a mix of sand and cement, although the surface is not extremely hard (I was able to make a hole easily with a chisel and hammer / it is rather "crumbly" afterwards)
- below this layer there should be about 30-40 cm of compacted sand (we had to level the heights around the house and sand was used here)

Now my question is how the subsoil should be constructed, whereby the current height definitely needs to be raised by 4cm (the running track of the sliding doors should be at the same height as the terrace slabs).

In general, I want to carry out the project myself and it would be great if you could give me one or two tips.

Many thanks and best regards
Thomas

I would first pour a concrete slab for the terrace and then lay the new slabs on top. This prevents sinking and unevenness, among other things. That’s how I did it at a house and found it great. Since the area is practically already prepared, in my opinion that would be a manageable effort and the laying afterward easier.

Should the old substrate be removed (at least partially)? With which material should the "filling" be done? Drainage mortar, screed concrete, flowing screed, leveling compound....?

Hi, I mixed quick-setting concrete with edelkies for my pool, moistened it, and laid slabs. It’s rock solid. Then the tiles on top.

Hi, I mixed quick-setting concrete with premium gravel for my pool, moistened it and laid slabs. It is rock solid. Afterwards, the tiles were laid on top

Thank you very much! Did you also lay 2 cm thick slabs? Did you coat the slabs with a flexible adhesive or bonding slurry?