Lessons learned while mountain building

A latex mold filled with paper mache pressed against the mountain

Back in September I tried two different methods for making rock castings: 1) filling a mold with papier-mâché and pressing it against the mountain while still wet, and 2) spraying Great Stuff foam into a mold and then pressing it against the mountain. The first method worked, but took awhile to harden, the second was a messy failure.

Later I tried filling a mold with papier-mâché and letting it harden in the mold before gluing the dry casting to the mountain. That seemed to work ok too. 

Masking tape holds still wet casting in place

The problem I found with making additional stand alone papier-mâché castings was they had a tendency to break before hardening because I failed to provide them with proper support during the drying process.

After some humming-and-hawing I settled on the first method of taking a mold loaded with papier-mâché and pressing it against the mountain while still wet. Sometimes masking tape had to be applied to hold everything in place while drying.

One modification to the process I made was to peel off the mold from the still gooey papier-mâché after around 8 hours. By that time the goo was firm enough to withstand the mold coming off without damage, and the now exposed surface allowed the casting to dry much faster.

Much faster? Hmmm, well, in my basement drying time of an air exposed casting could be anywhere from overnight to a few days depending on the thickness of the casting, the water content of the papier-mâché, and the workshop's humidity, which I attempt to control at this time of year with a dehumidifier.

Rock casting at Inspiration Point

I applied about 7 or 8 molds to the mountain to give rock-like three-dimensionality to large flat surfaces. Once they were hardened a lot of time was spent blending them together with carefully slathered on papier-mâché to create a unified surface. Surface detailing still needs some work, but the shapes seem to be ok. Well, except for the Granite Gate. I still haven't settled on the shape for that feature.