Earlier in the year I employed a contractor to replace the lead flashing around my chimneys - ironically I had previously contracted someone else to do this and they had done such a bad job I needed to redo it. They also repointed and reflaunched the chimneys too.
Prior to having the job completed it was quite obvious that the chimneys had been leaking, there were obvious signs of water ingress around the chimney breasts. A couple of months after the job was finished and I had repainted the area, I noticed damp spots appearing on my chimney breasts and tried to investigate why that might be so. After some consideration I'm not sure the issue is still the chimney: there may be other issues e.g. hygroscopic salt (it is an old house and at one point there would have been open fires) or render failure. However while investigating in the attic I discovered I could see slivers of light between the chimney stack brick and the lead flashing in a number of places. I link a video
and attach a photo of some of these slivers.
The question is, would this light be 'normal' or cause for concern? The extensive YouTube research (!) I have done on chimney flashing suggests that most people fix the horizontal edges of lead between bricks actually in mortar, but the vertical edges are effectively 'open' which could mean light would be visible? I'd like to think my contractor has done a good job, but do not have the experience levels to tell.
For reference here is an external view of one of the chimneys taken by the contractor just after he had finished:
NB - For background I'm not sure the damp spot issue is the water coming via the chimney stack anymore as there are also similar damp spots away from the breast on adjacent external walls; not really a question for this post just including for thoroughness!