Steel beam in concrete ceiling - how to plaster?

In our living room, we have two steel beams between the concrete ceiling. My plasterer does not see the gap between the individual concrete slabs as a problem and can close it.

However, he sees a problem under the steel beams. If he were to putty there, it would only hold for a short time.

Has anyone in this forum had to solve this situation before? What would be the easiest solution here?

How about simple battens and then sheathing with drywall?

We also have a steel beam in the living room, it will be plastered in about 2 weeks. Our site manager said that first a kind of mesh will be applied there, otherwise the plaster would not hold. I'm curious to see how it will be done.

Best regards
Sabine

This won't work with a batten. The recess is about 1.5 - 2 cm.
The problem with this "net," probably plaster mesh, is attaching it. Because you can hardly fasten it under the concrete ceiling. It will then protrude from the ceiling and say goodbye to a nice flat surface...

Our site manager said that first some kind of net will be applied there, otherwise the plaster wouldn't hold. I'm curious to see how it's done.

I guess the net will be attached with mortar or construction adhesive (not fully covered so that the plaster can flow behind it as well). But the plasterer should actually know this in more detail and it should be routine for him, so I wonder what kind of training he had. That he sees a problem here, I take as an indication that he is only "semi-trained" (even though it actually is a vocational training profession, but now probably one without a master craftsman requirement).

To explain it more precisely. Our ceiling will NOT be plastered. It is also not to be suspended with drywall, because the recessed spotlights are already planned in the concrete ceiling. So unfortunately, there is no option to apply mesh to the concrete ceiling.