> 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
>
> --
> To terminate puerile preservation prattling among pals and the
> uncoffee-ed, or to change your settings, go to:
> <http://maelstrom.stjohns.edu/archives/bullamanka-pinheads.html>
>
>
Ilene:

Since you have started with a mix design that is in the Type O range,
which has to reach 350 psi at 28 days under the ASTM C270 standard,
the 620 strength you are getting is not too surprising. But Type N
will not usually get you 750 psi, it will often reach 1500 to 2500 at
28 days depending on sand grading and cure regimen. I guess the
question is what you are really after. What makes you think it needs
to be higher than 620? How would you go about determining the strength
of the original mortar?

Cure time for lime is an interesting topic of discussion. Some say it
never cures completely, a theory to which I tend to adhere and to
which I would attribute lime mortar's long-term plasticity.

Edison Coatings, Inc.
M. P. Edison
President
3 Northwest Drive
Plainville, CT 06062  USA
Phone: (860)747-2220
Fax: (860)747-2280
email: [log in to unmask]
Internet: www.edisoncoatings.com

--
To terminate puerile preservation prattling among pals and the
uncoffee-ed, or to change your settings, go to:
<http://maelstrom.stjohns.edu/archives/bullamanka-pinheads.html>