FWIW, the MSDS of Chico A sealing compound says it is:

Fused calcium aluminate 60% - 70%
Plaster of Paris 30% - 35%
Portland cement < 4%
Crystalline silica < 2%

I'm not sure how the fused calcium aluminate changes the chemistry, but there is some discussion on line about using a sodium bicarbonate solution to attack plaster of paris. If that works, it would be a lot less hazardous than muriatic acid.

Cheers, Wayne