Long ago MR and RMC articles usually hinted at pouring plaster(of Paris), letting it set, washing with desired colour(differing colour/tones for additional batches), placing said lumps into a sack/cloth bag and munting them with a hammer to produce scaleable scree, talus, and waste rock.
This technique alleviated the use of rounded gravels derived from river run aggregates.
Just don't ask what issues eh!
UpSideDownC
in New Zealand