Natural hydraulic lime comes from burning Limestone. For a thousand years we produced our own supply & the country was dotted with kilns, the ruins of many can still be seen today.
In those times hydraulic limes were judged by their ability to set in water, being classed as ‘feeble’ ‘moderate’ or ’eminent’.
Modern day limes (imported from Germany or France) are classified by approximation of the same qualities: NHL 2 being the more feeble, NHL3 being moderately hydraulic & NHL5 being eminently hydraulic.
We are using NHL5 because of being situated close to the west coast & susceptible to much wet weather.
Lime mortar has to be mixed using accurate measurements.
The recipe here is 2 buckets of sand to 1 bucket of Lime.
Water is then added carefully by small amounts. The consistency of the mortar should not be sloppy, but a thick, workable paste. Excess water will lead to loss of strength due to evaporation leaving air pockets behind. Clean water is essential so as not to compromise the mix. We use fresh rain water.
These walls are roughly 46cm/18 inches thick, and have been built using mud mortar. This was common in the past. This dark brown mud came from beneath a peat bog and had a great stickiness and workability as a mortar, and was of course cheaper than lime mortar.
Lines are set up lines in readiness to build.
After having endured over a hundred years of erosion and neglect, the first restorative stone is placed!