Had a go with flour and water last week. It was probably my bad experiences of trying to mix flour into sauces etc that had been putting me off, but by being patient I got a good sticky paste. It does make the pm pulp more manageable.
The head at foot of this post is for a 'mild-mannered' PC character, and is modelled around a pm core, there is one layer of fine pm pulp, including whiting, and this was reasonably smooth, the face detail has then been further covered by a thin second layer of extra fine pm pulp with a higher whiting content.
Not a big head at 14cms as shown, the weight of 105g is very reasonable, but starting with a sturdy pm core the weight can start to creep up, and the Judy head (at bottom,) bit smaller at 12.5cms has reached 160g
To keep the weight down as the heads get larger, a polystyrene ball or balls or egg can be used, the ghost below is taller at 17cms but weighs 135g