I have not read the book referenced. But I would recommend wooden frame for shape, aluminum window screen stapled on frame to make desired shape and covering with paper towels soaked in a mixture of powered texture paint. This method was use by me in the late 1970s and probably was not use in the 1940s or 50s display layouts but I think it will give the same appearance with out the weight and cracking of plaster of Paris that was probably used on the earlier display layouts.
The below write up is from my OGR post linked below
https://ogrforum.ogaugerr.com/...ra-027-layout?page=2
The mountain frame was made from ¾ inch boards for a base and ¼ and 3/8 inch plywood framing to make the mountains shape. Care was taken to be sure none of the tunnel supports interfered with the train track and right of way. Tunnel portals were cut from ½ inch plywood. The mountain shape was covered by stapling aluminum window screen on to fill the openings between the framing and fill in the mountain shape. An access door was made in the side of the mountain to allow clearance of train wrecks and derailments.
View of Mountain with access Door for derailments
Access Door removed showing two Marx switches inside mountain
View Inside mountain showing framing and some window screen on left
Sears Textured Paint, a powder that was mixed with water to make a paste was used to cover the aluminum screen wire. Textured paint was used by painters to add swirls to ceilings to hide the tape seams and may not be available now but something similar should be available. It has proven to be a great mountain material and did not crack and is much lighter than plaster of Paris and is more durable than paper mache and not susceptible to bug attack. The textured paint was used to soak paper towels that were laid on the wire screen to form the surface. Several layers and coats were used.
5 pounds of Texture Paint was used and this one left over.
Charlie
