Fiberglass Cloth
Hate to be the "naysayer" on this but I've got a suspicion that fiberglass cloth is not going to work to well with plaster.
Especially the kind that's used in automotive repair.
Part of plaster's ability to bond to a surface is the ability of the surface to absorb the moisture from the plaster. Since the fiberglass cloth does not absorb water a bond may not be created. You may able to get by with a small area like Shamus' waterfall but large areas may be a problem.
A fiberglass mesh would work for a large area in that the plaster would flow thru the holes in the mesh and create a mechanical bond the same as it does with window screen wire.
That's the science lesson for today