Lime mortar

Your have to find out if there is any orders on the house that it has to be pointed with a certain material but if it was originally in line which I’d imagine it would then it would be a better job to do in a lime mix. As for cavity only way to tell would be to have it inspected or acess your loft and try and see from the eves

Put white vinegar on the existing mortar. If it’s fizz’s it lime mortar and would recommend nhl3.5 with grit sand and building sand

Easy ways to check Look at the brick bonding on the external wall: English/Flemish bond with headers visible → strong indication of solid brick construction. Almost entirely stretchers → could indicate cavity construction, although bonding alone isn’t definitive. Measure the wall thickness around a window/door opening if accessible. A small inspection hole/borescope can confirm whether there is a cavity.many Thanks RPM

For a house dating from around 1913, I’d generally expect the original mortar to be lime-based, so it should normally be repointed with a compatible lime mortar rather than a hard sand-and-cement mix. However, 1913 is around the transition period for wall construction, so you can’t reliably tell from the age whether it has solid or cavity walls. A knowledgeable surveyor or experienced traditional-building contractor can check the brick bonding, wall thickness and, if necessary, inspect with a small borehole or borescope before specifying the work.