Anybody want to weigh in on this?

Typically, we specify repointing mortar to match original mortar, based on laboratory testing for materials and proportions, expecting to see the ubiquitous Type N, 1:1:6, mix.  Further, we specify white Portland and .06 alkalinity.  This allows us to reject gray Portland with all its impurities, and locally St. Mary's cement which has .1 alkalinity.  Sometimes we just specify the Type N mix without testing, based on our experience for age of building and conditions.

So, when is it possible to allow a pre-mixed and bagged combination of these essential ingredients?  Spec Mix tries to fill that need, but I'm skeptical of any proprietary additions, which they deny they do, but are intentionally vague about the proportions.  They say their mix is based on performance and not proportions, so their Type N mix is just white cement and hydrated lime and clean sand, but they exceed 750 psi in strength.  Although typically their mix reaches 1,250 psi, as long as we test our masonry to be stronger than the mortar, where am I afoul of restoration practice.

Case in point:  our current contractor, highly regarded and very experienced, is working high on a platform and doesn't want the hassle of storing and site mixing his mortar ingredients.  Spec Mix is his answer.

I stand exposed and vulnerable, but willing to receive all your barbs and advice, and will do what I need to do, but perhaps with greater wisdom.

Thank you for being gentle and patient, as I strive to better understand this question of practicality in the field.   I'd just like to close the gap between what architects specify, and what contractors really do, assuming we're both doing our best for the building.


Ilene R. Tyler, FAIA
QUINN EVANS | ARCHITECTS
219 1/2 N. Main Street
Ann Arbor, MI  48104
ph: 734 663-5888
fx: 734 663-5044



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