The bricks need to breathe, and you’re slapping on a barrier to that causing more problems
Bingo.
If you trap moisture or try to block it’s progress it will just find a new route and being trapped will lead to stuff breaking down.
Chemical injection is a load of rubbish.
First find out where it is getting into the wall. If anyone suggests rising damp and chemical injection then show them the door. Fix/divert the source away from the wall in the first place. Then, as your wall isnt waterpoof so small amounts will still get in use a covering that can breath. Eg a paint on breathable membrane (vapour permeable) and then a breathable plaster. If it’s an old building I would always use lime. Expensive but worth it, especially in problem areas.