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We have recently moved into a 1960s built house with a large block chimney, which leaks around the top in the upstairs rooms. We have had a roofer in to replace the lead and rubbers, and had them back 4 times (no extra cost) to look at it again, repair pointing, etc. because the problem remains. As the winter progresses the dampness and evidence of leakage gets worse. The chimney is made of sandstone block which seems very porous, and definitely holds on to water, as shown by the dark patches in the photo. I'm now thinking we have to render to waterproof the whole thing to prevent it getting wet and soaking through. I'm trying to get a surveyor in to advise, but would welcome advice from anyone on this as rendering is expensive. I've considered waterproofing using something like Sageguard Stormdry, but I favour rendering for other reasons.

Hi garybarnes995
It would appear that there is no capping on the chimney, it needs to have an impervious slab fitted which projects around the chimney and incorporates a drip groove.
Once this is done you could treat the block work with silicone waterproofing liquid.
Regards S

There were slabs on top but these were removed by the roofer and replaced with flaunching. Was this a mistake?

Hi garybarnes995
Possibly that was a bad move. It’s unlikely that the flaunching will be non porous whereas concrete slabs would seal the top of the chimney.
Chimneys this size usually serve at least two flues - have some been sealed?
Regards S