Eric,

As those of us with offices on the refined and dignified East Side say,  fuck
'em.

This asshole (excuse me, I mean distinguished) Contractor chose to bid on
your project with specs that said (didn't they?) that you would not permit
the use of accellerators; he didn't take any exception to the specs that told
him that he had to provide blankets, temporary heat and and GOd knows what
else to protect the work; and (some other shit I can't think of right now).
Either he does it the way you spec'd and he agreed to perform the work, or he
can go fuck himself.

If, God forbid, the Owner is leaning on you to go along with this,  you might
wish to offer the Contr the opportunity to extend his warranty (by say, 5 or
10 years), and to include a provision that all future efflorescence (and
other defect that you can think of that might result from using this crap)
will be removed at no additional cost to the owner.  Offer to let the Contr
pay for lab tests on field-installed samples to prove to you and the owner
that everything  is hunky dory.

That should shut them up.

Ralph