Better minds can respond to this query ,but lime mortar absorbs water then at a certain point sheds it , salts are crystals that " bloom"with the wet dry process prior to Portland ,fort work was "capped " with Natural Cement (see conference with Mike Edison) this according to documentation found in the Army Corps of Engineers 1898 Why? because of its strength and ability to shed water -- To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: <http://listserv.icors.org/archives/bullamanka-pinheads.html>