Hygroscopic Salts on Chimney

[Monty_Stranger]

Hello

We have a 1930s house and blocked the chimney 2 years ago as below. This is an external wall.
Before

[GALLERY=media, 104200]Image0 by Monty_Stranger posted 29 Mar 2020 at 10:53 AM[/GALLERY]

After

[GALLERY=media, 104201]Image1 by Monty_Stranger posted 29 Mar 2020 at 10:53 AM[/GALLERY]

Mistake no1 - we didnt add a vent to the bottom - this has now been added by drilling holes in the plasterboard area and adding the vent

We also had the roof replaced at the time. Late year some damp patches started appearing halfway up the wall above where the grey plasterboard is in the photo above. These became progressively worse during the persistent wet weather this winter (I live in Glasgow). We had the chimney checked by a roofer who said the sealant was gone and water was getting in. He fixed it.The chimney "stack" is a metal flue pipe.
[GALLERY=media, 104199]IMG_1836 by Monty_Stranger posted 29 Mar 2020 at 10:53 AM[/GALLERY]
The damp patches now have salt deposits appearing. My amateur research tells me these are salt deposits
[GALLERY=media, 104198]IMG_1834 by Monty_Stranger posted 29 Mar 2020 at 10:53 AM[/GALLERY]

So how to fix- if i chip the plaster back then apply some sealant and replaster, will this work? Do i only need to be concerned about the damp areas or the whole wall? The damp areas have not become larger since we had the roof repaired and added a vent.

Any ideas as to materials etc? I am happy to give it a go myself but if too complex will call in a pro.

Thanks

 

[bobasd]

Presuming that you still have a flue going up an external chimney breast? do you have a pic?
Assuming no metal flue liner, did you originally sweep the flue before blocking it off?
There should be through ventilation bottom to top of the flue.
Hack off back to brick, and render with a 3:1 sand & lime mix with a limelite finish.
Hack off 300mm beyond any salt signs.
Dont use any sealant.

Why not read up on some of my previous posts about dealing with your situation?

 

[Monty_Stranger]

Thanks Bob - no we didnt sweep the flue. There was a gas fire there previously. I'll check out your posts. Thanks again

 

[bobasd]

a 1930's house will definitely have had a solid fuel fire.
still dont know if there's a SS liner in the flue?
still no pic of the c/breast?
perhaps its time to get someone on the stack again - to check & photo the condition of the metal terminal, the flaunching and the flashing.
go in your loft and look for staining around the external chimney breast?