In the garage, screed floor, or is there something better?

Hi,

I agree.

Mastic asphalt with a dense coating on top also works. But I can't tell you which is cheaper.

Personally, I would probably choose the composite screed and then coat it as described above with an epoxy resin-based coating, or you tile it and use something epoxy resin-based for grouting the tiles. That is probably cheaper because you would have to sand or shot-blast again for the coating, and you would basically have to do that already for the composite screed.

Best regards

Hello "Zettel159".
You have already received some practical hints here as a posting.
Ideally IT WOULD HAVE BEEN best to raise the floor slab directly by the now missing height.
Underfloor heating WOULD HAVE BEEN also possible as so-called "concrete core activation," meaning: the heating elements are embedded in the concrete. But not a solution for the missing build-up height.
Liquid asphalt is ruled out, as 10cm height is generally not built with liquid asphalt (but only 30-35mm per layer), and for such a small area no asphalt worker will come with a 5m³ (to be heated) liquid asphalt kettle!!
The only (and also sensible) way is to apply a cement screed CT30 in multiple layers, each with a nominal thickness of 50mm, bonded onto the floor slab.
It must be noted that – depending on the floor plan of the garage – a slope or, for 50m² total area, possibly even a central drainage channel should be taken into account. I omit the necessary surface protection here in my reply, as it was not requested in your inquiry.
---------------
Good luck: KlaRa