Efflorescence/damp on wall

[aparry93]

Hi all, I cut back the old damaged efflorescence/damp plaster to the brick here and dry lined the back wall. However due to the tie in with the undamaged wall and timber mantle I decided to dry it out and take a chance and dot and dab which I know people will disapprove on here. About 8 months have gone by since replasteting with gypsum and unfortunately the efflorescence has returned pushing the paint and creating like bubbles just on this corner. Can people advise what they think could be the issue here. What is also odd is that it looks like they have merged the new fireplace with an old one. So hidden behind this corner wall is the old chimney I think. I’ve even tried selling into the brick and I’ve drilled in about 400mm deep and the brick is wet! I have attached a photo of the outside and the chimney in question is the white one in the photo.

 

[Cherryburn]

On the scale of things I disprove of, dot and dab plasterboard is probably nowhere near as bad as dry lining or rendering direct to brick. It's at least easily reversible, and there's a bit of an air gap which can sometimes help dry things out.

It's a bit hard to tell exactly what is going on here, but chimneys are pretty notorious for issues as a result of the soot buildup over the years of use. It contains a lot of salts and corrosive chemicals which can attack building materials if it ever gets moist enough to seep through. It's rarely an issue while a chimney is in use, as the heat keeps the brick bone dry. But once a chimney is left disused (?), it's important to keep good ventilation through the stack at the top and bottom of each branch. This may not be the case in your example if the fireplace has been further bricked up on the inside, presumably with cement. That gives nowhere for any moisture to go but out through the plaster on the other side. Moisture which could be coming from the ground, from any leaks or even just from humid air within the house condensing onto a cold surface.

As for remediation, I wouldn't rush into anything. If you uncover some of the brick again, see if you can get it to dry out at all. It can take a long time for brick to fully dry out, but if it remains wet then that points to another problem that you may need to fix. A leak from the roof, an incorrect chimney pot cap being used, potentially some gaps in the pointing, or otherwise a subfloor issue. You can get products which claim to neutralise the salt, though I can't speak to their long term efectiveness. You may need to consider a wall covering which would allow any moisture to continue to escape, lime plaster or a small ventilated cavity.

 

[aparry93]

So I decided to peel the paint to see what was hidden. Plaster looks like it’s wet in the areas I’ve used the adhesive to dab the boards…I know this as when I knock the wet patches these are solid and the areas dry are hollow. Could this be moisture from the adhesive? However this was done around 8 months ago. Or is this just a pathway for the moisture from another source

 

[Stevers]

In my experience pink gypsum plaster is extremely intolerant of salts and/or damp, in time becoming hygroscopic. It could also be said that plasterboard is a layer of water soluble gypsum wrapped in cardboard - a building material for controlled conditions!

My basement chimney breast has been transformed simply by replacing the cement render and gypsum plaster with NHL render/plaster. The remaining walls are still tanked, but the chimney breast now 'breaths', it no longer smells damp, the salting has stopped and the new NHL lime plaster still looks good after a year.

 

[aparry93]

Well tonight escalated. I decided to remove as I could tell something wasn’t right. I even found slugs. How would you recommend repair. There is also an old hidden chimney. You can see on the return side of the red brick I have removed an old brick to access it and it looks like it is full of rubble

 

[Stevers]

In my basement chimney breast the bricks had rotted on the inside and front of the builders opening , so I replaced the rotten bricks using some bricks that were already here and happened to be more or less the right size being a lot thicker than a modern brick, but only fractionally thicker than the bricks I replaced.

It struck me earlier in the thread that there had been a fireplace in the corner on the right, and that there had also once been a 9" brick wall coming away from that corner going across the room where the beam now is - hence the mess that corner is in. My OCD would require me to rebuild in properly bonded brickwork and NHL mortar - getting rid of some of the salt contamination in the process. As it will all get covered up, it's a good place to have a go as a DIY'er. Then render and plaster using NHL mixes confident that you will have greatly improved your chance of success.

 

[aparry93]

I’ve drawn in blue the hidden chimney and took a photo of where I have removed a brick from tinder the chimney. I thought maybe doing a smoke test to see if there were any signs of leaks and then creating and air gap by building a stud wall and dry lining it like I’ve done with the back wall.

 

[Stevers]

The redundant flue will need an air vent just above the skirting board.

 

[Cherryburn]

If that's against the external wall you showed us earlier you could vent it outside through the cavity instead, cut down on internal drafts. Air gaps can be useful, but if you're just doing it to cover up the problem without dealing with the root cause then you risk creating a stale trap for mould.

 

[aparry93]

If that's against the external wall you showed us earlier you could vent it outside through the cavity instead, cut down on internal drafts. Air gaps can be useful, but if you're just doing it to cover up the problem without dealing with the root cause then you risk creating a stale trap for mould.

Thank you. Will look into how I can gain access from outside on the weekend and vent outside. Venting inside feels like the wrong solution as it will create a cold draft. Below is an old photo.. but I will try and lift this slate highlighted as my assumption is this is part of the buried chimney.

 

[Stevers]

The slate might be keeping water out of a bend in the flue rather than where the flue previously exited. Count any pots and allocate pots to flues assuming that they can't cross over.

We have two ground floor redundant flues with vents above skirting (elephants feet on the pots) and have never noticed a draught. I reckon that they very gently suck rather than blow in almost all conditions. My basement chimney flue (with a gas liner) is vented to outside at the base and through missing midfeathers at the top to elephants feet on adjacent pots, and whilst that's a recent innovation it too seems to be working well.

 

[aparry93]

So after doing a smoke test by putting a smoke pellet in the hidden chimney. The gable end ground roof extension cap end was smocking. Mainly from this end cap that was terribly loose as shown below (lead corner). I imagine rain has been getting in here and making the old chimney moist. I would say this is one of the root causes. What’s your thoughts? Also I have no idea on best method to repair this corner cap end. Any suggestions? Thanks as always

 

[aparry93]

So to keep you posted. I managed to open up another hole to find the old chimney full of debris up to 1.5m above floor level. Have cleared out as far as practical