Eric,

We had to look at this situation a few years ago, in connection with a
large repointing project in Chicago using our pre-packaged/pre-colored
Spec Joint 46 Type N mortars. The contractor had been instructed to
store the bags in a heated area until just before use, to pre-wet the
masonry using hot water, and to stop work by 3:00 PM or when the
temperature dropped below 25F.

That has worked well in previous winter repointing work, but
the "heated" storage area in this case turned out to be the roof
stairway enclosure which was reaching temperatures of ZERO F
overnight. That explained why the mortar was freezing in the mixer at
35F.

We have tested a variety of winter admixtures, at least for their
initial effects on set time, color and strength. We found calcium
chloride to be the most effective in terms of set time, but the worst
in terms of effects on color - sometimes it darkened the mortar, other
times there was efflorescence. There is also the potential problems of
introducing corrosion inducing material which can affect metals
embedded in masonry assemblies. While considered harmless when used at
low levels (typically <2% on cement weight, I believe, according to
ASTM mortar standards), I would hesitate to allow the use of anything
with the potential to do the harm that calcium chloride can do.

We ended up using MORSET without apparent detrimental effects on
either color or performance. We specified exactly how much was to be
used in each mix, based on the mortar's cement content, and this
solved the unheated storage problem.

> We are having a real winter here in NYC this year and I have a few
projects
> that contractors and owners want me to allow the use of mortar set
> accelerators. They think this will allow them to work unprotected in
any
> temperature. I have always rejected accelerators due to problems
with bond,
> efflorescence, etc. and that we have successful, yet expensive,
> recommendations in our specs including heating masonry materials,
> windbreaks, blankets, etc. I was hoping some of you more "chemically
> inclined" BPers could help me explain more precisely why the
following are
> bad:
>
> *       Euclid, Euco Winter Admix. Active ingredient appears to be
Calcium
> Chloride.
>
> *       Grace, Morset. Active ingredients appear to be Calcium
Nitrate,
> Calcium Nitrite, and N-Nitrosodiethanolamine.
>
> Please be as detailed as possible.
>
> Thanks,
>
> Eric Hammarberg
> Director of Preservation
> Associate
> LZA Technology
> 641 Avenue of the Americas
> New York, NY 10011-2014
> Telephone: 917.661.8160 (Direct)
> Mobile: 917.439.3537
> Fax: 917.661.8161 (Direct)
> email:  [log in to unmask]
>
>
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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

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To terminate puerile preservation prattling among pals and the
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