Render cracks on external wall, no crack on internal walls

[propertystress]

Looking for some advice on a property. Cracks in render are where extension (circa. 1970s/1980s) meets original building (circa. 1920s). Survey came back to say there’s potential progressive movement. There are no render cracks on the ground elevation, damp cause is fine and there’s no rising or penetrating damp. Drains were visually checked and looked to be flowing, no previously reported issues with drains.

There an no internal cracks at all on this wall or anywhere else in the house.

Does this look like a subsidence issue or something else?

 

[^woody^]

Progressive movement or foundation movement?

The crack looks a bit too even to be foundation movement, and there would normally be cracking internally, on the ceilings and on the other side of the extension too.

What's the white staining? New paint?
The brown staining is curious. If its rust, then perhaps inappropriate metal ties to the main house starting to corrode?

Some render would need to be knocked off to investigate the cracking, and normally the opinion of a structural engineer would be better than a surveyor.

 

[propertystress]

Thanks for your response Woody. We’re wondering if the previous owners tried to patch it up hence the white paint, much like you we’re also curious about the brown staining. One thought was if previous owners had tried to fill the crack with sand and cement?
Which also leads us to wonder if there were any internal cracks and they’ve been boarded over to hide them. If this was the case would the cracks usually reappear inside after a while?

 

[^woody^]

Repairs internally should be visible, as would recent decoration or overboarding.