Lime mortars – why use them?


first law of property ownership is that systematic and regular maintenance is always best. If a building falls off the so-called ‘plateau of good repair,’ it is expensive to haul it back up again. Dry rot, for example, is almost always a consequence of timber being in contact with wet masonry.


A


But how does one keep stone and brick masonry dry? Firstly, of course, by maintaining roofs, gutters and pipes, and by keeping a watch for obvious damp patches. If green staining becomes evident, a problem has remained unobserved and undiagnosed for much too long. Secondly, by ensuring that moisture which has got into the wall by whatever means evaporates out and does not become trapped behind impervious finishes.


In order to have a proper grasp of this, it is necessary to understand the nature of


traditional building, the process by which buildings used to be built, and how it differs from modern construction.


Traditional building has its origins in the pre- industrial age, when buildings were made from natural, locally sourced materials. In the UK, earlier buildings of timber were superseded by walls of stone or brick, bedded in lime mortar, plastered internally and frequently also finished externally with a floated or thrown plaster coat and/or limewash.


ll owners of old buildings face the challenge of maintaining and repairing them. The


Top: A late 17th century house in Fife, whose stone walls are kept dry by a permeable ‘overcoat’ of thrown lime harl and limewash


Above: Lindisfarne Castle off the Northumberland coast, with walls brought to a flat surface, with more lime mortar than stone


Continued >> Listed Heritage Magazine January/February 2020 89


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