ᐅ Closing an Opening in the Screed for a Construction Staircase

Hello everyone,

Our construction staircase was removed yesterday. Naturally, there are now two holes in the screed where the construction staircase was fixed to the floor slab.

Our site manager said these should be filled as follows --> insulation first, then filled with screed. With this method, should there be a membrane between the insulation and the screed? If yes, what type of membrane should it be?

Our stair builder suggested that these holes could also be filled with two-component expanding foam. It would provide insulation, be sufficient for the load, and would be quick and straightforward. Vinyl flooring will be installed as the final surface.

However, the idea of using expanding foam feels a bit unusual to me.

What do you think?

Thanks

No expanding foam, please!