: The local rock gym has an employee who makes holds. He's experimented with
: several materials. Wood does not make good holds, due to cracking and
: splintering and relatively low friction and wear resistance. The holds he
: makes now are a combination of resin (polyester, I believe), chopped glass
: fibers (for strength) and coarse sand (for texture).

Your mentioning polyester resin made me think of automotive filler putty--it's a pre-thickened polyester resin. Bondo 'n Sand would be a perfect hold-making medium. (With little need for the non-boatbuilding type to have to learn about thickening resins, etc.)

Shawn

: He mixes it to a
: dough-like consistency, shapes it to his liking, impresses a steel washer
: into the surface deeply enough to recess the head of a 3/8" allen
: head bolt, then pokes a hole through it. Once fully cured, they work
: great, provide excellent friction and wear like iron.