Brown stains on newly plastered chimney breast

[Tash123]

hi everyone, first post on here. We have recently had our spare bedroom plastered and over the last couple of months this damp has spread and is now showing brown spots. We are in the process of getting quotes for removing/re rendering the chimney stack. Can anybody advise why it is brown? Is removing the chimney stack the correct action to take. We have spoken to our neighbour a sit is a party wall and they have the same problem on their side. Strangely the wall above in the loft seems to be bone dry.

 

[Wayners]

Chimney Cowl might stop water coming in.
You need to investigate.
You have water getting in there.

 

[88v8]

this damp has spread and is now showing brown spots. We are in the process of getting quotes for removing/re rendering the chimney stack. Can anybody advise why it is brown? Is removing the chimney stack the correct action to take. We have spoken to our neighbour a sit is a party wall and they have the same problem on their side. Strangely the wall above in the loft seems to be bone dry.

I would leave the stack. A future owner might want it, and no stack often spoils the look of the house.
The brown is soot leaching through the parging and the mortar, due as Wayners says to damp in the flue.
This happens because of people leaving the pot uncapped &/or blocking up the fireplaces with no air vent. The rain comes in and eventually this is the result. Removing the stack will not remove the problem once the soot starts to leach through.
First, the chimney needs to be capped off with a ventilated pot cap, and the fireplace should stay open to create an air flow.
As to the stains, you can try to cover them with a stain block such as Zinsser BIN, or if the stains even come through that you will need to use a barrier such as Foildamp but then it would need wallpapering to cover the Foildamp.