Guy King wrote:
The message
from Phil Armstrong contains these words:

Just don't get sharp sand (for making concrete etc etc); you need soft
sand (or whatever builders call it).

Soft sand stains really badly - it's got a lot of fines in it - almost
clay. This is what makes it so stable when firmly compacted.

I've yet to find a good substitue for "real" play sand - apart from
beach sand.

There's a BS something or other product which is crushed glass. It's
safe to handle and has been crushed and screened so that it's no more
damaging than sandpaper (which also uses crushed glass).

Back in out play pit constructing days we used to use silver sand, which
is simply a fine white sand. I think it is dredged from the sea, washed
and screened.