This is a clean, washed river sand that’s specifically intended for rendering and plastering use.Plastering sand has finer particles than sharp sand or building sand.
Generally, in any plastering work plasterers are used natural sand, crushed stone sand or crushed gravel sand.
In general, good plaster sand should be sharp, with a diversity of particle sizes, and clean. Sand should be sharp and angular, not worn and rounded. Imagine trying to build any kind of structure out of balls vs blocks, and the reason for this becomes obvious.