SBR slurry works, ive used it today. It stops water.
But as mentioned, some houses are made with lime which has to breathe. If you have a stone wall. which has lime mortar on in, and you hack it off, and stick plasterboards on it, skim it...it will look fantastic. But down the line it will all go wrong. Stuff made and used in the last 25 years or so, is modern and meant for modern techniques. This is what i know and was taught.
Old houses need to be aprroached differently. And what you might find is a builder or plasterer who cant be a***d to do it properly, and can stop water ingress by slurrying it. If you dont have lime render etc then this could be your answer. Do you have any pictures you could post of you internal and external walls? if they are just brick then that will make things easier.