Mixing and making Hot Lime mortar

We will only recommend hot lime mortars these days.  

The reason for this is a little complex chemically, but it's lost in the mists of time.  This is how lime always used to be made.  You took limestone, burned it, added water, and mixed sand with it to make mortar.  It fizzed, hissed and got very hot - and then slowly set to the lovely breathable, flexible lime mortars we see in surveys.  

More recently, hydraulic (not hydrated) lime mortars have been developed and widely sold (Called NHL - or Natural Hydraulic Lime.  In 3 common flavours - 2.5, 3.5 and 5 - where the numbers refer to set strength in Newtons)  These limes are easy to use - like buying a bag of cement.  They set quickly, and work very much like cement in that you get a first 'set' and then harden over weeks as true 'carbonation' takes place.  The catch is that these seem to be setting much harder over time than we thought they would.  Which makes them less flexible and less breathable.  New research is underlining this fact.

So, to solve the problem, we go back to traditional hot lime mixes.

They are easy to make a little harder if needed - just add a pozzolan - brick dust for example, and it makes the mix a lot tougher and harder.