What are you going to attach the plaster to? Are these going to be like a painting on the wall but in relief? If so, you could make a wooden frame with a wood backing in which to attach some screws too. These screws would be beneath the surface of your plaster and just give it some added strength like rebar does for concrete.

Adding fiberglass to the plaster will give a lot of strength as well. There are different types of fiberglass. Some are shredded and can be added directly into your plaster and other types come in sheets that like thin fabric. You dip the fiberglass fabric into the plaster and let it soak in and then lay the fabric into a bed of plaster that you’ve already applied to your sculpting surface.

Look forward to seeing what you are working on.:clap:

It would be heavy at 2″ thick by 4′ to 5′. Of course, attaching it to studs would be the way to go and it would hold. I’ve cast a lot of my sculptures solid in plaster and they are table top size (19″ tall or so) and very heavy.

Here is a plaster product that I have seen sculptor friends use that is lightweight and easy to use. https://www.sculpturedepot.net/clay-wax-tools/product.asp?Forton_MG_GFRC

I know I’ve seen wall relief plaster videos on YouTube. One guy sculpted directly onto the wall. If you want to make a frame and would like the piece 2″ thick, then perhaps get your general form built out with some chicken wire and hang plastered fiberglass over that. The voids behind will lighten the piece. If you use Forton MG, that will lighten it even more.