Check your link -- it doesn't seem to be working.

Shrinkage - One of the facts of papier mache is that when it's wet, it swells, and when it dries, it shrinks.  I think there is some law of physics at work there. I think strip or patch-type PM may shrink less than the pulp, as the pulp has more air/space in it than smoothed-down strips would.

Room-temperature drying will help to avoid distortion more than heated drying. A small fan may speed drying for you, but not a heated fan.  Also, the least amount of moisture that you could incorporate into the PM would be beneficial.  For pulp, you are limited in that respect, as it requires a certain amount of moisture for you to be able to manipulate it. If you press out too much of the water, it will be hard to work with.

Buying cheaply - most of the commercial mixes contain ground or shredded paper with some kind of binder/adhesive. Some contain plaster, which limits the working time due to the plaster hardening.  None of these mixes dry quickly. Amaco Claycrete is just paper and adhesive (possibly methylcellulose).

Casting - Yes, you can use either plaster or plastic/vinyl molds.  If you are using interior molds, the PM usually shrinks and pulls away from the mold. Partial exterior molds (the PM doesn't encircle the mold) should pop off once you get them started. Any PM material wrapped around edges must be removed or filed off.  An encircling exterior casting must be cut off and then fastened back together.

Sanding the completely dry piece and then coating it with several thin coats of gesso on the visible side will give a smoother finish. If you aren't intending for the PM parts to be finished, be very careful in your production methods for a smooth (or appropriate) finish. PM is not the easiest thing to patch in visible areas.

Good luck, and welcome to the board!

Sue

Liam

I'll send you a recipe for pulp that I find works very well.  It's not worth buying stuff when there is so much free raw material.

DavidO

I haven't posted it because it is fairly similar to the fine pulp (porcelain) recipe that is already on by Martin Favreau.
DavidO