Re: Repair broken plaster sculpture
Might want to read the instructions on any other glue than Elmers, rubber glue and contact cement are the only glues I know of that are applied on each piece, let DRY and then pressed together- every other glue I'm aware of - especially Elmer's and white glue- you simply apply a thin coat and clamp or weight over night.
I had a 600 POUND architectural concrete bust that was in a building fire and a section about 75# had cracked and broke when it was moved, I glued that back together with Elmer's white glue and it held perfectly fine for years. It only came apart when the entire sculpture was SOAKED for 2 days in a fire sprinkler flood I had by sitting in 6" of water, but when left in place and dried out the glue re-activated and hardened up again as before once the WATER dried out.
So unless you are planning to soak this thing in the bathtub, adding patching plaster or spackle is not going to affect the glue enough it will fall apart.
I have worked with plaster sculptures and broken mother mold shells in restoring/repairing and the plaster has to be SOAKED in water and totally wet, otherwise if you try adding more plaster on it or repairing it- the plaster just sucks the water out of the fresh plaster and it doesn't work well. You then have to keep damping the stuff down till the fresh hardens and then the two plasters usually have different hardness.
Use the Elmer's white glue, it's the easiest most simple fix
If all you are doing is pulling a mold off this thing, glue it and patch with spackle, bondo or plasticene, or plaster in small bits and damp the area you are working with a spray bottle of water and while the repair hardens- don't soak the thing in the bathtub in other words.