Mortar

I have been reading through a lot of conservation literature
recently in working on a book, and am stumped by something I have
found repeatedly in abstracts about mortar in buildings.  Cement and
polymer-based mortars are said to be incompatible with original
mortar components.  What does this refer to--chemical
incompatibility of some kind, or a difference in physical responses
to moisture, or something else?  How exactly does this manifest
itself?  I would appreciate an explanation, as there is obviously
something here I just don't get. Thanks,

B. Appelbaum

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                 Conservation DistList Instance 10:105
                   Distributed: Friday, May 30, 1997
                       Message Id: cdl-10-105-002
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