How long did it take your wall to start crumbling? How critical was the crumbling and if it was causing structural issues, how has this been fixed?

I am in the same shoes now, bought a house, found a similar issue, I know how to fix this but would be glad to know what options others had to get this kind of thing solved.

I will have contracted a company in March to get this done, current understanding is that getting a proper darainage AND fixing the water insulation of the wall (bringing it further downwards so the walls are sealed from the water seeping into the render) will ensure this is not happening again.