anyhydrite or hemihydrate?

Hello,

Liquid screeds come in (at least) two types: AnhyidrIte (CaS04,H20) and HemihydrAte (2CaSo4,H2O). One is Gypsum and the other, supposedly is Plaster of Paris--but untill now I always thought Plaster of Paris and Gypsum were the same thing. Actual chemical properties don't concern me. Practicalities, however, are a different matter. So:

1. Which is better? In particular, which is stronger? (Do either react with iron (such as with steel reinforcing mesh?)

2. I don't see Plaster of Paris taking tile cement very well. Any comments on that?

3. Are these screeds PURE Gypsum and/or Plaster of Paris? I.E., are they only that? Or is the Gypsum/Plaster of Paris merely their main constituent and to which other materials are added to make them more durable and stronger?

Thanks in advance,
Phrixos

have a look at mapei topcem instead.
I'm assuming that you are looking for a screed to go over underfloor heating.
With both types of screed you've mentioned your floor covering installers have to know what they're doing to avoid any failures. They both take longer to dry enough to install flooring (reach 75%rh or lower) whereas the topcem is very rapid (do a google search)

Thanks Petest67. Haven,t heard of Topcem before. I'll look into it.