We have been renovating a 19th century granite cottage. We have decided to keep one wall, with the fireplace, as exposed stone. The stone is mainly granite. The wall has originally been built using a lime mortar. We wanted to have the wall re-pointed in order to bring out the chracter of the stone and to make good the crumbling mortar pointing. We have just had this done by a builder who has worked in thos area for over 50 years. however, he has used a cement and builder sand mixture as the mortar. We have since found information on the web that says that lime based mortar should never, if possible, be replaced with cement. we are now considering removing the cement and replacing it with lime based mortar. It seems a drastic step and wondered if any one has encountered this before? should we leave the cement to dty out completely before removal? Any other thought would be welcome.
Hard (ie 1:3) cement mortar will eventually prove less than
perfect for that job. Stone walls in lime mortar move gently
with changes in humidity and temperature and the pointing
will come away in places, for sure.
My advice would be to dig it all out (set or not) and replace
with pointing in a 1:1:6 or 1:1:8 mix of Portland cement, slaked
lime and soft sand, raking the joints as deeply as possible to get
a good fill of the new pointing mix.
To prevent future flaking and shedding of dust, wait about a
month after the pointing and then use 2-3 coats of VERY well-
thinned PVA size over either the whole wall or just the pointing,
as you choose.
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