Comment 68417

By heritage (anonymous) | Posted August 24, 2011 at 18:23:58

The first mortars were lime based. We know now that lime mortars used in the 19th century were softer than the stone or brick of the stucture being constructed and that the mortar was able to allow for the passing of water vapour through the seasons. Two critical properties that allow older buildings to survive today. It is very unlikely that water will become entrapped within these older materials.
It is a mistake to use modern portland based cements that are harder than the old stone or brick in historic buildings. Water vapour or moisture in the air is not allowed to pass through portland and the building stone or brick will break before the cement when any very minute seasonal shifting occurs in the building. I have seen the resulting broken building stone when water becomes trapped behind portland based mortars and the freeze thaw cycle blows it apart.
Buildings always move and seasonal humidity will try to equalize itself in buildings. They need to breathe.
The crafts people that built our historic buildings knew that they needed to work with the natural environtment.

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