Damp patches on chimney brickwork - possible causes?

[alexeix]

Hi,

My girlfriend's house is a Victorian end of terrace property, with 2 chimney stacks on the end wall.

We've noticed that there are damp patches on the external brickwork from around waist height extending up approximately 2 metres.
Below waist level, there is rendering along the bottom of the wall, so the damp is not evident on the outside of the house, but inside, we can see it on the exposed brickwork inside the fireplace and creeping onto the slate floor inside the fireplace (which is unused).

We haven't noticed any issues with the guttering and I think it would be a bit strange for any water discharge to be specifically occurring on each chimney anyway.

The next house along (also an end terrace), also seems to have the problem, so does anyone have any ideas what might be causing it and if it's a reason to worry?

I wondered if the chimneys could be letting in water and may need to be capped??? Seems unlikely though.

Thanks in advance!

 

[cotswoldbuilders]

Check all the pointing, fit rain guard cowls to chimney pots and check flaunching, plus the lead work.
You still need ventilation to the stack.

 

[noseall]

Google 'hygroscopic salts' and have a read.

Chimney masonry, particularly chimneys that have burned fossil fuels, are saturated with these salts.

Also, plastered-over sooted bricks can be a nuisance as the blessed stuff insists on bleeding through the plaster.