Hair is used internally and externally. Mind you I have found plenty of internal lime plasters with no hair at all!
There is a huge variation in the amount of reinforcement (hair, hay, straw) that was used as well. Mike.
Yes, as filler. Just mix ground rice and water, and there ya go. Did it as the shops were closed, out of filler, needed to finish off etc. It works fine. Being starchy, damp and rats can both affect it, so not recommended for damp or ratty situations.
I assume its the starch that does the binding, and the fact that theres a lot of hard non-starch in rice maens youve got a non soluble matrix glued together with starch, hence little to no shrinkage.