i would suggest same as alan and gary.
what puzzles me is that you did not recognise that this screed was different than sand/cement/
i am assuming that you have never laid on to anhydrite before and therefore did not recognise that this screed could not be sand cement
hi Jonny, I wasn't sure but did quiz the customers and architect on my thoughts of it being a Anhydrite on pricing the job.
I was unsure because you find a lot of freshly laid anhydrite screeds look very similar to some special lafarge, cemex, tellings screeds these days.
bearing this in mind, The architect was telling me it was concrete (definition: rough building material made from a mixture of broken stone or gravel, sand, cement, and water)
on this information I proceeded.