Cover the terrace with granite - prepare the substrate beforehand

Hello, I have a terrace behind the house that consists of about 40cm of concrete/screed, it has been like that for about 10 years and over time the concrete is slowly crumbling due to the back and forth sliding of the chairs. Now I want to put granite on the slab. Unfortunately, there are slight bumps and cracked spots on the slab. So now I would have to work with leveling compound?

How exactly do I proceed? Build a formwork all around and seal it with silicone? to prevent the compound from running out?

Unfortunately, the slope also goes towards the house, at first I wanted to reverse it but now I thought about installing a rain gutter, one that is drivable and then lead it into the downspout of the roof gutter. There is no direct connection to the house, about 30cm distance, only one step is actually the terrace door. Size of the terrace is approximately 24m²

Can someone give me tips?

Best regards Ronny

hello, I was at leymann Baustoffe today to inquire about leveling compound, it would cost about 1000 euros for my area and thickness... of course that's too expensive. Also, the seller said that due to the lack of a roof, frost damage could occur in the joints. He suggested that I lay the slabs on about 2cm of gravel and fill the joints with grit. That should be safer, sounds pretty reasonable. Can the edges be bordered with angle brackets? What would happen on the side where I install a rain gutter, since the water there would first rise about 5cm (2cm gravel, 3cm granite slab) and then drain away, frost risk?

Really dangerous business, because the surface water must be drained, gravel bedding = water storage = everything will crack apart during frost, especially if the concrete is already crumbly and water penetrates somewhere, it will blow away under the slabs even more since no evaporation/drying by air and sun takes place anymore.

What height can you make? My recommendation as a technical advisor in building materials trade for civil engineering and landscaping: repair the concrete surface and keep the slope, lay granite slabs (I assume you want to lay slabs, right?) on pedestal supports (e.g. plate supports from Kaim), leaving the joints open.
It would be best to seal the concrete surface using an epoxy primer or something similar. But that is a high-rise construction area, e.g. Remmers products, I’m not that specialized in that, I only do it for partition walls in silo systems.

I would also install a drainage channel, e.g. from ACO, at the end of the terrace, the Euroline or Hexaline would be sufficient. But keep in mind: sealing to the house is necessary because drainage channels are not a watertight system (joints)
Or you can have one integrated into the ground.

I wanted to waterproof the terrace beforehand with a bitumen membrane. Around the edge, I will now set up curbs for the exact height. Unfortunately, everything that goes on now is too high, so I want the buildup to be as low as possible. I have already looked into the pedestals, but I don't like them because of the open joints and also because they are very expensive. Is there any way to leave something open under the slabs for the water, somehow make slots in the curbs and use drainage fleece so that the water can escape but the gravel stays in?

best regards Ronny