Chimney damp issues

[Jammy_Jim]

Hi all,

Thanks in advance for helping. Basically, as can see from photos, we have damp patches on our chimney stack. It's out of use and tops have been capped few years back (before our time).

You'll see from photos damp is in 2 rooms, that are back to back, and share the chimney stack. 1 of the rooms is an extension (room with shelves) to main building and we're not sure if the damp is caused by stack condensation in both rooms or possible the flashing that connects the annexe to main building has issues and water getting in. The damp is at the same height and place on opposite sides of stack. In 1 of the rooms you'll see a vent, we had this previously core drilled as we had a damp issue collecting in cupboard built-in to the old fireplace, and were told ventilating would solve that.

Cheers for your help.

J

 

[opps]

Not my area of expertise but I have worked in houses where the home owner had damp on the chimney breast. They fitted caps over the pots that allowed a degree of airflow.

They still had damp patches on the chimney breast.

They had already paid thousands to have the walls repointed in the hope that it would sort out the chimney damp spots.

I redecorated the room and used SBR and stain blockers (over easter 2021). Winter 2021, the stains came back.

Mr customer spoke to a damp specialist.

The guy didn't charge my customer for advice, he did however tell him that it was down to hygroscopic salts. Chimney breasts are full of soot, the soot absorbs moisture thoughout the year and dumps the moisture through the plaster during the winter.

The free advice was to remove the plaster from the brickwork and use sand and cement.

 

[mcprinter]

Have had this in my 1930s. Damp on breasts upstairs and down.
Lots of work on the chimney stack that never solved it in the 20 odd years we have been here.

Stack now removed to below roof level and slated over.
Stained plaster removed from breasts and redone. Seems to have sorted it finally.

 

[Jammy_Jim]

Thanks both for replying @opps @mcprinter ! Along time, but an update that it turns out we had a leak, which could have been for a year or so, on the channel which sits above and between the 2 rooms in the photos (one is an annexe to main building). We also vented both chimney at the bottom.

Water was seemingly coming in to the chimney stack and progressing down the shoulder of chimney flue that (we believe) each room shared.

The stain and blistering became a lot worse than in the photos. Now it's fixed, we waited about 6 weeks to dry out before redecorating but some stains and blistering coming through again (albeit much less), and worse on the thicker/bigger chimney.

Could this be because the salts are still doing their thing and sucking the dirty chimney moisture through? Or does it just take a very long time for old chimney bricks to dry out, potentially months?

Thanks,
J