Cellar wall repointing

As its a solid wall in a 1920's cellar it would probably need tanking to stop the damp,(usually from the outside) Rake out old mortar and re-point using damp a proof additive to the mix may slow it down

Give the wall a good clean down then flush point the wall then give it a good coat of tanking slurry but if the floor is wet then a membrane and float pump will be needed without inspection first Good luck

Rake out the joints it is probably lime mortar so re use a lime mortar mix 3 and1 ratio, we had a property in Cornwall forever damp and weeping, to combat that problem we used a mix of cement and SBR brushed on in 3 coats , plastered over the top no problems after.

Efflorescence is a sign that moisture is passing through the wall, so simply repointing may not solve the underlying problem. However, if the mortar is crumbling, repointing the affected areas can help protect the brickwork and prevent further deterioration. On a property of that age, it’s important to use a suitable breathable mortar, such as a lime-based mortar where appropriate, rather than trapping moisture in the wall. It would also be worth identifying the source of the damp so the root cause can be addressed when your budget allows.