What can be used to level the concrete stairs?

Hello,

as mentioned above, we need to level our concrete stair steps by about 4 cm each. One step more. There are 45 steps! Vinyl sheets will be glued onto the steps.

The site manager says that screed would be optimal, but that is apparently also the most expensive.
An acquaintance who does screed, but not stairs, said it would also work with a quartz sand filler mixture, then online it says cement mortar also works.
I had also read the word synthetic resin mortar.

Now to the experts on the portal, what is the correct approach and how should we proceed?

We already have an offer for screed: €3000 plus accelerator €10 per step.

Thank you very much in advance.

At our place, a height adjustment was made elsewhere with manually mixed screed, so that should definitely work.

I think I heard once: If tiles were an option, Styrofoam boards of the respective thickness could be laid and tiled over. That would be an extremely inexpensive option. Steps in front of bathtubs and such are also made that way. But no guarantee whether that would work for entire stairs.

Statements we have received so far:

Site manager: Screed
Floor layers: Sand & stable
Construction expert: Screed
Screed company that does not do stairs: Quartz sand + stable filler

The idea with the Styrodur sounds good, but it is difficult to impossible on uneven ground. At €3000 (that's how much the screed for the whole house cost here) it is also clear that the costs lie in the labor and not in the material. Do it yourself? Who messed up the height and has to pay for it?

Unfortunately, this is anchored in our contract with the construction company. Compensation for the stair step including the covering is the responsibility of the client. The house acceptance has already taken place as well. Therefore, it is out of our own pocket. Our flooring installer is also our current neighbor. He only charges €20 per step for sand & standfester mortar/filler. We also have a warranty there. But what is the best way, if there is only one.

You've really picked a tough job with vinyl there. A neighbor also covered his concrete stairs himself and was busy for at least a week with about half as many steps. Formwork, pouring leveling compound that seeped everywhere, etc. ... tremendous work. And cutting and embedding rails on every step, etc.