Cavity Block wall abutment to solid stone wall question

[RobertG]

Hi, 

My builder has just used cement to fill the join between the two walls. The cavity block wall and the stone, rubble and lime mortar wall. I can see the damp penetrating the blockwork but the lime mortar wall dries well as it should. 
 

Can someone advise what I should expect for this area of the construction? I can’t see this as being acceptable. Photo provided.

[RobertG]

Bumping this up. 👍

[jfb]

Why is it damp? 
how else is it going to be constructed? once the block wall is weathertight what is the issue?

[RobertG]

On 25/05/2026 at 12:21, jfb said:

Why is it damp? 
how else is it going to be constructed? once the block wall is weathertight what is the issue?

Hi, 

 

I’m led to believe that a vertical DPC would normally be used between a cavity wall and the original building’s wall. I think the damp is leaching from the stone wall with lime mortar into the block wall. Ther’s not a lot of definitive information readily available. 
 

Thanks, 

 

Robert

[torre]

21 hours ago, RobertG said:

vertical DPC would normally be used between a cavity wall and the original building’s wall

 

On the inner leaf of the new wall - if you want something to show your builder then LABC publish renovation guidance that covers this including a diagram on page 14...

 

 

[ETC]

DPC is in the wrong place!

[ETC]

 

Edited Wednesday at 15:59 by ETC

[ETC]