In article ,
Simon Avery wrote:

Building sand can have high concentrations of salt in it - "washed
sand" is commonly available and may be implied depending on area, but
there's unlikely to be anything else - any mortar additives are put in
during mixing, or with the cement - never with the bulk like sand,
AFAIK.

As Cormaic pointed out, builders' sand has not had salt in it for many
decades - at least not if bought from an even half-respectable person.


Regards,
Nick Maclaren.