Plaster/Paper Mache Pulp
plaster/paper mache pdf
Materials
Soft white paper, good quality PVA glue, Calcium carbonate (ceramic whiting, slaked plaster, joint compound plaster, chalk or even cornflour)

Instructions
Boil shredded paper on a low heat for 1-2 hours to break up fibers
Keep enough water for paper to float. Blend with a stick mixer or blender. When cool, squeeze out enough water for paper to still be slightly squashy.

Combine 1 part paper with 1 part PVA glue, mix until smooth.
Add 2 parts calcium carbonate or similar powder.
Mix in powder, one part at a time until desired consistency is achieved

Notes
Use less paper and more powder for a smoother mix.

Plaster Clay
Materials
PVA glue, boiled linseed oil, calcium carbonate (ceramic whiting, slaked plaster, joint compound plaster, chalk or even cornflour)

Instructions
Start with 1 part PVA glue, gradually add up to 4 parts joint compound plaster or the equivalent powder to the PVA, mixing until smooth.  Add linseed oil until clay is plastic to work with but not oily.

Notes
I came to develop these recipes through looking at Gesso, a plaster slurry used to cover walls and canvass.  They used slaked plaster, which is super diluted then dried plaster.  Ceramic whiting is a very close alternative which does not react with water.  The mache pulp can be mixed and stored for long periods in air tight containers.  Ordinary plaster does not work as the plaster sets too quickly.  Joint Compound Plaster is chemically set and takes a lot longer to set than ordinary casting plaster.  Mache made from it can’t be stored however. 

More information for joint compound plaster recipe can be found at
http://ultimatepapermache.com/paper-mache-clay  She uses flour in her recipe which will give a stickier mix.  Gesso recipes use honey or rock sugar.

You may need to experiment with different materials.  Some joint compounds apparently do not work.  Different types of PVA glue will give different drying times and strengths.  A high quality pva glue will make a mache pulp that only needs to be a couple of millimeters thick.