Steve,
    But it lasted the first 100 to 150 years, that seems pretty good.  Plus,
the sand is essentially the same fabric as the original.  I don't think the
original masons did anything special before mixing other than a wash.  Do
you know otherwise?
    We have been using local sands both from rivers and beach for some
twenty years (and the masons fifty to sixty) almost exclusively on granite
or trap rock walls, we then lightly etch the surface to expose the aggregate
for a match.
    I understand the salt issue, but have experienced little evidence that
it has a significant play.  I have noticed a ton of efflorescing on every
brick pointing job at Yale where the sand has been carefully spec.'d.
Thoughts?
Best,
Leland