I have a technical question for youz (gender-neutral) guys:

We specified a mortar mix of 1/4 part white Portland cement, 2 parts
hydrated lime, and 7 parts sand to match the historic mortar.  The brick
are really hard, testing out at 14,500psi, so mortar strength is not the
problem, unless it is too weak.  Initial tests of our mix are just that,
too weak, starting at 620 psi, and not increasing at 14 days.  Something
might be wrong with the mix.  This is all using too much time, and the
contractor is anxious to start his repointing and rebuilding at repair
areas, and we keep saying we need the mortar mix to test initially at
750 psi, with indications that it will increase at 14 and 28 days,
before his work can proceed.

Should we give up and switch to 1:1 1/4: 7 to make it more like a
standard Type N mix, or should we hold out for the hybrid historic
mortar, when strength is not the problem?  Our testing consultant would
like us to stay with the high lime mix, but I'm feeling time pressure to
revert to the standard. 

I know I won't get a straight answer, but I might find a reply on this
email list that I had not, even in my wildest dreams, imagined possible.
Surprise me...  Thanks.


Ilene R. Tyler, FAIA

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