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as lime mortar but some or all of the sand is replaced with ash. It was
forbidden on many building projects as it was more prone to failure
than lime mortar. In many cases it was used anyway on the non visible
areas, as coal ash was something one had to pay to get rid of.

Having hit some with a drill a few years ago it amazes me the house that
was made with it was still standing. It was like flaky pastry.

--
Skipweasel
Pay no attention to that man behind the curtain.