External crack cover - fibre?

[88v8]

Bathroom extension, single storey, 60s, hard concrete blocks, cavity. About 10 x 15ft.
Slight horizontal cracking in the cement render most of the way round the three side. Mainly along the same course at window cill level about half way up. External cracking only.

Been filled and painted by PO, cracked again.
Hasn't become a structural problem, yet, and no damp, yet. But...........

Could be a bonding failure, or perhaps corroding wall ties?
Anyway, I'm not going to take the walls down to fix it.

So, what I'd like is a thin-bed render perhaps with fibre? that won't crack.

Any ideas, experience please?

 

[ted456]

You need to post pics but at first glance what you describe is classic wall-ties rusting and swelling in the same bed.
From the outside why not remove a bit of render and blockwork at one single tie, and examine its condition - but dont attempt to pull it out.