Random damp patches on wall

[DIY67]

I have a spare room with a cold outside wall that has always had condensation hence drips of water. I have hung insulation lining paper with Warlock thermal paste to the left side of the chimney breast. The wall is much warmer. So far so good. I am about to hang it on this side of the chimney breast but there are random damp patches I can't fathom as it isn't condensation (no water run marks). Even stranger are the damp patches on the chimney breast itself which has a gap between it and the outside wall. In fact, the downstairs fire is being used so there is warm air between. The chimney itself was pointed 2 years ago, as well as a new roof. No leaks at all there. and I have storm dried about halfway up the outside of that wall (I need to get higher with some scaffolding to finish) I have also invested in a dehumidifier. I can open the window as much as I can but not in cold weather as I* will lose heat.

So apart from not knowing what is causing these patches, I am hoping that covering the wall with the insulation paper will stop it. I shall try and get higher up (perhaps extended paint roller up a ladder) to finish the storm dry as soon as we get a couple of rain free days as I suspect the odd spayed bricks may be the culprit. The house was built in 1883.

 

[foxhole]

Damp on and around chimney breast is usually down to unventilated and or uncapped chimney pots .
The fireplace would normally keep the area dry as it heats and causes very high levels of ventilation .
Remove the heat source without capping the chimney to reduce rain ingress and adding ventilation result in damp.

 

[opps]

It might be hygroscopic salts in the chimney breast itself. They absorb moisture in the warm months and when it becomes cold and damp, they dump them through the neighbouring brick work.

Take a photo from further away (showing the chimney breast as well).

 

[DIY67]

I have covered the recessed walls with the lini8ng paper and it has made a huge difference. The walls and room are no longer cold. Just can't fathom why the chimney breast which has a cavity behind it has damp. I was going to leave the chimney breast and paper with normal lining paper using thermal paste instead of standard wallpaper paste ?

 

[opps]

I have covered the recessed walls with the lini8ng paper and it has made a huge difference. The walls and room are no longer cold. Just can't fathom why the chimney breast which has a cavity behind it has damp. I was going to leave the chimney breast and paper with normal lining paper using thermal paste instead of standard wallpaper paste ?

Erm... perhaps Google "hygroscopic salts".

I am a decorator, I have come across similar problems. If it is down to the salts, by the end of the year, you may see damp patches appear through the lining paper.

The chimney is likely to be full of old soot- that soot absorbs moisture and in the colder months it dumps the moisture through the existing plaster- and lining paper... I am not making this up.

 

[DIY67]

I have noticed Jackdaws nesting for the first time in our chimney but there are two pots, one for the current open fire downstairs and the other for upstairs (the studio room in question which used to have an open fire) They have nested in the unused pot.

I can see that the salts may come through the normal lining paper but I very much doubt they will come through the polysyerine backed insulation paper. They dont just appear on the chimney, they are also on the walls, near the top of the ceiling which are nothing to do with soot.

23 years ago I had some old wardrobe doors dipped and stripped to the original wood. to this day they still attract wet patches on the wood despite taking off and drying in the summer sun. I have even jet washed the doors to flush out any remaining chemicals used for stripping. all to no avail. my only option is to perhaps wax them.

 

[DIY67]

Erm... perhaps Google "hygroscopic salts".

I am a decorator, I have come across similar problems. If it is down to the salts, by the end of the year, you may see damp patches appear through the lining paper.

The chimney is likely to be full of old soot- that soot absorbs moisture and in the colder months it dumps the moisture through the existing plaster- and lining paper... I am not making this up.

Well after almost a year on I can feel the lining paper (despite having polystyrene backing) feels damp in places, as does the ceiling paper. We have just had the chimney swept (after 2 years use) and about to have a log burner installed with metal flue. I am hoping the combination of a clean chimney and new burner will help keep the breast, and area around dry and even slightly warm during winter.

 

[davidm1969]

Good luck! Lining paper however waterproof was never going to solve whatever is the cause of the damp behind it tho was it? Polystyrene is not entirely waterproof so not a surprise moisture has got through it

Condensation happens from lack of ventilation open the windows use a dehumidifier add window vents etc.

if not capped chimney could be letting in water from above plus hydroscopic salts and if not vented at top and bottom could also cause damp.

Old crumbling /soft mortar could also be letting damp through so could cracks (these do need to be filled before applying stormdry)

Stormdry helps water repel but like any product I'm not sure if it makes bricks and mortar 100% waterproof in all circumstances if there's enough driving rain it will fail?

Also if you read up on cavity walls sometimes if something bridges the gap you then get a cold spot...could be what's happening in the cavity behind your chimney breast?

Hope that helps rather than hinders!

 

[mrrusty]

I have had the same issue in a 1902 house. A 100% cure from what I have personally tried seems to be to strip off the salt contaminated plaster, seal in any salts with an SBR slurry (not sure how necessary this step is) and then fix plasterboard with a foam adhesive which damp and salts can't pass through (unlike water based dab adhesive that they can).

If you have a ventilated cavity, you could insulate internally at the same time - we have; we used loads of insulation on internal face of external walls, and 5 years on no issues with interstitial condensation (we feared this was a risk, and I discussed with our BCO at the time and we concluded that the risk was mitigated by the ventilated cavity, which has proved to be the case). However, if you have a solid wall I would not rush to insulate without further investigation.

they are also on the walls, near the top of the ceiling which are nothing to do with soot.

It's not just soot - it's combustion gases as well. In our house all the walls exposed to a room which had a long-term coal fire are salt poisoned. The walls alongside a chimney particularly.

Your chimney IS capped isn't it? an open chimney will have loads of water coming down it - think bucket stood out in the rain...

 

[Koolpc]

Condensation could be the cause, linked with the salts too...

 

[DIY67]

Ok, we have the log burner installed with metal liner, a more durable high grade. All chimney pots are now capped which were previously open (one even had no pot for years with gaping hole until replaced a few years ago) I Wass told by the guy fitting the flue on his cherry picker that he has rented out many houses for many years and in his experience nearly all causes of damp in chimney breasts are caused by not having pots capped. He also told me that people make the mistake of sealing the tops with concrete which only causes condensation. This and the combination of the warm flue has improved things already as the walls don't feel damp to the touch. I also have a dehumidifier on hand. Since having these improvements (including new loft hatch the house feels so much warmer.

 

[mrrusty]

Heating, dehumidifiers etc are all good remedies against condensation. However, if salts have migrated to the surface of the wall, they will be pulling moisture from the room air whether it is condensing or not. The more humid the air, the more it will pull. A dehumidifier will definitely help. Ambient room air at 70% humidity holds about 14g of water per m3. If you pull the humidity down to 50% it still contains about 10g/m3.

If it's raining don't forget it's 100% humidity outside, and warm air can hold a lot more water vapour than cold, so you have to think about condensation and salt growth as having separate but related causes; one thrives on high humidity, the other depends on temperature differentials and whether surfaces are below the dew point.