This update is overdue.
My recommendation for papercrete at this point, after a few years of experimentation, would be to start with that good ol' three parts substrate to one part Portland cement mix. Since the days of my mower-towed "mini-mixer" I have dabbled with using cellulose insulation, peat moss, vermiculite, and sand as substrate and have come to rely on the three to one mix, substituting one substrate for another depending on it's use.The recipes I posted years ago made for a weak mix. Two parts paper to one part sand to one part Portland cement would be a better starting place. I mix smaller batches by hand these days. The papercrete wall in the picture is covered with a heavy layer mortar made of sand and Portland cement and laced with either joint compound or builder's lime added for plasticity. Both the wall and the sculpture still stand. Just remember that everything posted here is in the spirit of experimentation.
Thanks for reading.