Hi we are at Beaulieu (87) and the mortar is crumbling away and there are lots of holes in it where masses of flies are entering the house. Any suggestions please. We can see the flies actually going in through the wall!
Thank you, this is a very good site. The book I am using is 'Lime, A Guide to The Use of Lime Mortar in Historic Buildings' Published by South Somerset District Council. Although it is very good on the lime elements it is a bit succinct on the sand.
One of the problems I saw in France with builders is that they tend to mix cement in lime mortar. It negates the qualities of both products and is deadly with soft stones and brick buildings.
Not wishing to contradict your book but a good mix of all grades of grain size is the normal preferred/strongest mix.
It of course depends on the size of the joints, thin/fine joints in brick walls will require finer sand than a rough stone wall with larger joints.
The issue with fine sand is the higher surface area contains more water so higher evaporation when it's drying can cause shrinkage and cracking.
I used fine washed sand with slaked lime with very good result. My book on lime says 'fine sand'. It is not really the sand that matters but the lime does.