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Why is it so common to use render in the first place then? Genuinely interested. There certainly are internal issues which I'm seeking to address (cold / damp bathroom) but the render is clearly damaged, letting in water and getting worse.
Unfortunately as this is a shared freehold, that's probably not an option.
Polygon-
I think it started off purely as a fashion thing, when bricks were considered ugly in the post-war concrete era - hence the appearance of pebbledash, etc.
Since then it's often used as a 'solution' to damp, because people think that damp is only ever caused by water getting in - a myth seized upon and perpetuated by damp proofing companies. If you have properly functional guttering, then a well-pointed brick wall will not get so damp from rain that the damp comes all the way through to the inside, and between rain events the wall will dry out fine on its own.
The trouble is, once you've slapped impermeable cement render all over bricks then there's no way that any damp is getting out - and any that's caught inside - perhaps by a crack in the render elsewhere, or an internal leak - will be prevented from escaping.
NB If you have a wall cavity, then external render is less of an issue, but I'm assuming that's not the case
BobbyBriggs
I expect the damp in the wall is caused by internal factors rather than anything to do with the external render - unless there's leaky guttering or something like that.
The render, however, will be preventing it from drying out. Walls need to breathe, and the 1960s-present fad of slapping cement render onto external walls is a hideous and costly way to prevent damp walls from drying out.
Hack off all the render and in a few months time the wall will have dried.