Chris Plastow
Patches half way up the wall are normally caused by incorrect plastering height when doing replastering after a injection job. From your description I would say the wall was treated about 20 - 30 years ago. This is caused by salt migration. The new plastering height should have been 1.2m. If the damp patches are restricted to between 1.0 to 1.2m that is it. Replace that section of render. My advice would also be, get a damp proofer to check it.
