External wall question

[adaw24]

Hi,

Would anyone have any idea what this mark is on an external masonry cavity wall (circled in yellow)? The paint has a hollow sound when tapping on it in that area in some parts.

Thanks in advance

 

[tell80]

There's a definite "line" of disturbed render - its probably a case of the render being blown due to damp getting behind the render.
Render should finish above the DPC - at the moment your render has bridged the DPC.
The render should finish with a plastic BellCast.
Where the render is in ground contact it draws up, by capillory action, moisture behind the render.

You could knock off that patch & re-render when installing a BellCast?
Any signs of damp inside the structure?

 

[^woody^]

There's a definite "line" of disturbed render - its probably a case of the render being blown due to damp getting behind the render.
Render should finish above the DPC - at the moment your render has bridged the DPC.
The render should finish with a plastic BellCast.
Where the render is in ground contact it draws up, by capillory action, moisture behind the render.

You could knock off that patch & re-render when installing a BellCast?
Any signs of damp inside the structure?

Your hypothesis on the cause does not explain why the issue is not along the whole length of the wall.

Nor why cracked blown tender is not cracked on the the surface.

Factoid: damp does not blow render.

 

[adaw24]

There's a definite "line" of disturbed render - its probably a case of the render being blown due to damp getting behind the render.
Render should finish above the DPC - at the moment your render has bridged the DPC.
The render should finish with a plastic BellCast.
Where the render is in ground contact it draws up, by capillory action, moisture behind the render.

You could knock off that patch & re-render when installing a BellCast?
Any signs of damp inside the structure?

No signs of damp inside from what I can tell.

 

[Nige F]

In that case leave it alone

 

[Old Salt]

There are parts of that wall going the same way. Zoom onto the foreground of the second highlighted pic.