How can I stop damp coming through wall?

[mrrusty]

@noseall has the answer in post #48. It's salt contamination, which once in the bricks/plaster, draws moisture from the room. The answer is to isolate the salts from the room. The easiest way is to strip it back to brick, and fix plasterboard using foam adhesive (that the salts can't cross - if you use wet dabs the salts get drawn through to the surface of the PB as the water in the dabs evaporates). Reskim and job jobbied.

These guys suggest a membrane to isolate https://www.tracebasementsystems.co.uk/post/damp-chimney-breasts, but I've found using foam adhesive works well in my house.

 

[foxhole]

Damp on thick wall internally , would that have been the original rear wall before extension was added? In which case poor roofing where it meets rear over the extension will allow rain straight down into brickwork .

 

[ree]

OP,
As mentioned above in a couple of posts: what your pics show is hygroscopic chemicals that originate in the flue or flues in your chimney breast.
1. Open any blocked fireplace, & sweep the flue.
2. Also sweep any open fireplace flues.
3. IOW. sweep all your flues.
4. Your rear elevation pic shows soot penetrating the brickwork at the base of the stack - ie it shows unswept flues, & possibly unventilated flues.
5. Flues need through ventilation from fireplace to stack terminal.
6. Mentioned above is the possibility of water penetration at the abutment of the (failing?) extension roof & the rear elevation? Its a possibility?

7. From the affected chimney breast remove all plaster back to brickwork.
8. Render the chimney breast with a 3:1 mix of sand & NH lime - skim with a remedial finish such as Limelite.
9. Dont use any slurries or additives - slurries can cause condensation. So can a cement mix.
10. Any use of any kind of plasterboard can cause other difficulties.

 

[mrrusty]

Any use of any kind of plasterboard can cause other difficulties.

We can agree to differ on that. My suggestion is not theoretical - it's what I have done to completely cure similar problems in 120 year old houses.

Why on earth would you use a breathable plaster? The water in the plaster will absorb the salts in the brick and they will be deposited on the surface as that water evaporates and the plaster dries, leaving them there to cause further problems!

And as to slurries causing condensation! - condensation is caused by air carrying water vapour reaching the dew point. It will occur in or on any material where the temperature gradient is appropriate!

 

[ree]

I'm afraid that you sound very theoretical.
Hygroscopic problems are not be "cured" not even "completely cured" - they are simply controlled.
Using plasterboard can create further problems - its a method that seems to have come into prominence with you tube as an "easier" hopeful alternative to the traditional rendering method.
You have a peculiar notion of what happens as render dries - salts may appear on the surface 20yrs later but not immediately after drying.
Plaster is not render.
Condensation can form on slurries.

 

[mrrusty]

I'm afraid that you sound very theoretical. Except everything I suggest on here is the result of personal experience
Hygroscopic problems are not be "cured" not even "completely cured" - they are simply controlled. Yes, by isolation as I suggested
Using plasterboard can create further problems - its a method that seems to have come into prominence with you tube as an "easier" hopeful alternative to the traditional rendering method. That's because isolating using plasterboard is an efficient method of isolation and control
You have a peculiar notion of what happens as render dries - salts may appear on the surface 20yrs later but not immediately after drying. The water in the render/plaster evaporates over a few days. The evaporation process deposits the salts on the surface in the same few days, beecause the evaporation takes place from the surface.
Plaster is not render. Quote from elsewhere "Plastering is the intermediately coating of building materials to be applied on the internal facade of concrete walls or blockwalls. Rendering is the intermediate coating for external walls only"
Condensation can form on slurries. It can also form on bananas. What condensation appears on is purely a function of humidity and temperature