Subfloor question.

[Gkular1]

I'm hoping someone can help I'm having a right nightmare.

I've got a suspended jousted floor. UFH heating guy has placed celotex between the joists and then a dry mix over the pipes. The screed finishes level with the joists.

Builder has then laid 12mm OSB ( very badly)

The flooring guy will lay 6mm ply and then vinly flooring on top of this.

My question is, the 12mm osb , can I lay 18mm instead or will this be too thick as it will have another 6mm ontop.

In some places there are no joists but solid floor. The builder has had to glue the floor here but not very well and it's a bit bouncy and loose on the edges. How can I secure the floor here, what glue should be used as there are UFH pipes