pointing stonework

[iandandav]

Most of the stone (sandstone) and lime mortar built houses around where I live have been repointed with a portland and sand mortar.

I have read that this is not a good idea, and I have noticed on many of the houses the stone is spalding. I dont know if this is just natural due to the age or whether it is down to the repointing.

If its the repointing Im curious to know if its just due to bad repointing, allowing water into the joint or if its an incompatibility of the stone and mortar, either mechanical or chemical.

Id like to hear peoples opinions on this as I will probably be repoint my own house some time soon.

 

[^woody^]

The inflexibility of cement mortar causes the stone to fracture and fall away either side of the joint

The actual finishing of the joint can accelerate this with certain soft stones too, so sometimes the pointing should be left proud of the stones and not flush

 

[stuart45]

You can brush use a churn brush to finish off the joints with lime mortar.
Do it the next day.