Limekilns and Lime

Just six County Waterford kilns appear...

Just six County Waterford kilns appear on the list of structures in the National Inventory of Architectural Heritage (NIAH), website at www.buildingsofireland.ie there may well be many more around.

Lime kilns are the commonest kind of kiln in the countryside. They are often squarish rubble stone structures with a cylindrical cavity opening at the top about two metres across in which layers of broken limestone rock and fuel (coal or wood) were piled on top of each other.  An arched alcove on one side at ground level allowed the bottom layer of fuel to be ignited so that all the layers would burn, eventually leaving a mixture of ash and whitened lumps of burnt limestone, known as quicklime, to be taken out through the alcove.

Quicklime was light and cheap to transport but it is a very dangerous material to handle.  As quicklime it was used sometimes in burying fallen livestock as it quickly corroded the flesh down into minerals-an indication of just how dangerous it can be. Wetting can ignite it. But for use as fertiliser or for making building mortars the quicklime has to be slaked; thrown into a pit of water by someone wearing protective clothing and with eyes well shielded.  The water literally boils in the pit with the heat of the chemical reaction and, depending on how much quicklime and water is added, the result is a heat-dried powder or an underwater putty.  Slaked lime is now produced much more safely in factories and both powder and putties are available to builders.
 
Limes differ in how hydraulic they are.  This reflects the wetness of the conditions under which a lime mortar will set.  A wet bridge base needs an extremely hydraulic mortar and an internal house wall needs none. Limes produce mortars that "breathe" and are often specified for use on traditional houses originally built of stone and lime mortar.
 
Cements are made from burnt clay minerals and produce more brittle mortars that do not "breathe" or "move" so well. Limes need less energy in their production than cement does and so less Carbon Dioxide (CO2) is produced by the factory.  Lime mortars actually reabsorb a lot of CO2 as they harden.