Mike,

My solution is just one approach to a problem. If the site of the work(especially if it is large and takes a considerable amount of time to complete) is in a location where it may possibly show for a long long time, it may be best to insure that the surface is of the best quality and craftmenship. It is possible to paint a fresco in a studio, remove it from the wall, and transfer it to a light-weight fiber glass surface. These mounts are easy to install, do not have a heavy load,and may go on a variety of surfaces. See fresco museum in Pisa. Yes, there are a variety of board surfaces that work well with slaked plaster. See this website or email Gary. The instruction,artists,and projects I have worked on have followed more traditional methods and steps that have proven successful for centuries; this is why I would offer such advice. It is just one suggestion to consider. You are right to think carefully about a surface because so much rests above it. Good luck.

Mozart