Repointing a couple of areas to try to stop leaking of rain water through wall.

[Peterwats23]

I need to try and seal between some of the stones above the front door and bay window to stop rain water ingress. I dont have the normal lime mortar joints but instead the very thin joints.
Does anybody know what this is? And, can I lime mortar in areas where I think rain water might be penetrating?
The stone work is a bit crumbly on the outside and needs scaling back with a little care. This is due to a false concrete brick affect being stuck to the outside with cement mortar in its history.... the horror!!
Anyway if anyone has any insight into this type of stone joints please let me know.
Thanks!

 

[Stevers]

Looks like they've been close bedded with a very rich fine grained (chalk?) lime mortar - the original craftsmanship being of the highest order.

 

[stuart45]

The stonemasons job in the winter months was inside cutting all the stones to size. My daughter used to own a house in Bristol built in the 1600's that although was a random rubble construction the majority of joints were around 2-3mm.

 

[Stevers]

My builder was working on a local mansion after he finished my house. He and his merry men spent that winter in a nice dry shed facing up stone ready to repair the long boundary wall in the better weather.

 

[a twig]

At the risk of being a potential downer - how hard is the white mortar?

I only ask because it looks pretty bright, and if the wall has been messed about with there is a chance that the mortar could have been “touched up” or re-pointed with some masonry filler or similar which will be very hard and not great for the stone.

The good news is if that is the case, it is pretty easy to remove with a thin stone cutting disc on an angle grinder as long as you are careful.

If the mortar is not rock hard then you’re probably fine and can ignore the above

 

[Kearn]

I would be thoroughly investigating where rainwater may be getting in, particularly if above doors/windows. Those incredibly tight joints are unlikely the culprit…they also don’t look like they need anything doing to them, assuming original chalk rich mix and that they are indeed not touched up with inappropriate modern muck. Even then…