Dale,
Unfortunately, I did the latex mix so long ago that I don't remember, and I've moved several times since then so I don't know how well it held up. But I suspect it has done fine since it is/was out of sunlight and relatively protected by carpet/flooring. The thing that sticks in my mind that I got off the internet is that "latex and plaster don't stick to each other," but that was in the context of using latex as a mold for a plaster casting and not as an integral part of a plaster mixture. I think I will experiment and see what happens, and based on the results, either abandon use of latex with plaster or proceed to use it on creating my layout scenery base.
