So, the good points of using the Oasis styrofoam as a modelling base:
* doesn't crumble
* easy to carve
* can be moulded with fingers
Not such great things about using it:
* it isn't very strong
* it isn't that easy to apply the Papydur to
I can't get hold of any proper carving poly blocks so need to make the best of what I have to work with. I discovered after a bit of experimentation last night that I need to cover the foam shape with PVA glue (undiluted because otherwise it just soaks in) to seal the block first. It needs sealing because otherwise each new application of Papydur seems to lift off what you just applied. It also takes off a layer of green flocking!
Papydur is the powder version of paperclay that I bought from the EU and can't read the instructions on the pack! You mix it with water and once it dries even a thin layer is like rock. So I am using it as a base layer over my fragile foam shapes. Once they are dry I will cover them with pre-mixed paperclay such as LaDoll. Took some terrible photos earlier (snowing again) so will post better ones tomorrow.