Damp patch on wall at floor level where chimney breast was removed.

[mr_chaela]

I've been doing some renovation work on a semi-detached bungalow where the chimney breasts were removed some 15 years ago. When the walls were skimmed a stain was noticed on the wall at floor level where one of the breasts had beem removed but it was perfectly dry and thought to be 'historical'. However, we now find that when it rains the patch becomes damp and when the rain stops it dries out.
I have looked in the loft and there is no sign of water penetration. Next doors adjoining chimney breast has been blocked off (no vent installed) and an electric fire fitted but they have no signs of damp.
A local roofing firm has been called in and they are 99% sure the problem is not coming from the adjoining chimney.
The patch is approx. 3 feet wide rising to about 1 foot high in the middle and extends across the floor by about 1 inch.
The problem had not been previously noticed as the wall was papered with a very heavy vinyl with a large sideboard stood in front.

Any ideas as to the cause.

 

[bobasd]

what you say seems to be a case of hacking off all gypsum plaster back to brick, and 300mm outside any staining area.
then rendering back up with a 4:1 mix of sand and lime and a remedial skim finish after removing any traces of soot or contamination on the brickwork.

check and inspect the other removed c/breast area.

why not post photos showing the stains and the relative positions of your c/breast old position, and the neighbour's c/b?

the neighbour,
would do well to have their flue swept and vented at the top, and at the bottom just above the blocking plate insert another vent.
if you have a single brick party wall then there's a possibility of their flue being all sooted up and affecting your wal - but its only a possibility.

 

[HairLoss]

I don't know if this is relevant but in my Victorian terrace the hearth sat on a pile of earth. Imagine the chimney breast stretching down below the floorboards to the ground and then being filled up with soil to floor level and concreted over.
The result is effectively a sponge sucking up water from the soil into the walls.
This might be the case with your bungalow.

 

[mr_chaela]

Sorry for delay. I will be at the bungalow tomorrow. Will take photo's and post them.

The other removed chimney breast area is fine - no signs of damp whatsoever.
On Sunday the chimney pots are to be capped and a thorough inspection of the roof/stack undertaken to rule that out as a source of water ingress.
I will also be meeting with the neighbour's son-in-law and will explain his need to vent the blocked off chimney.

Thanks for the help.

 

[bobasd]

hairloss,
what you describe is the typical construction of older hearths: a brick fender wall, with a soil infill, & a concrete cap.
fwiw: just search on here for fender walls - infill - or hearths. or look up some of my recent posts on the same subject

 

[bobasd]

OP,
if you still have chimney pots on your stack then simply dropping in "mushroom type" air vents will give protection & ventilation in one go.
ask for photos/video before any work & after the job is finished.

 

[NeoL]

I don't know if this is relevant but in my Victorian terrace the hearth sat on a pile of earth. Imagine the chimney breast stretching down below the floorboards to the ground and then being filled up with soil to floor level and concreted over.
The result is effectively a sponge sucking up water from the soil into the walls.
This might be the case with your bungalow.

Same here. I've been investigating online about this because I have had stains just above floor level. I realised the hearth was filled with earth, plus a thin layer of mortar.. it has been soaking the area. Also because behind the fireplaces once the breast is removed, the dpc is literally non existent, it is easy for damp to rise. It seems a common feature.

 

[mr_chaela]

Photo at last. The damp patch doesn't show up too well as it's quite dry at the moment - it shows more after rain.
I noticed today that the cement/concrete hearth infill has blown.
I wonder if I could dig it out and replace it (with appropriate dpm) without disturbing the plaster and skirting. Obviously I'd have to undercut the plaster back to the brickwork. Just thinking of saving time and effort.
I'm surprised the damp has risen so far up the wall and such a short distance across the floor if it a problem with the hearth infill dpm.

Chimney pots were capped today using C-Caps and a few broken tiles replaced. The pots and stack looked in pretty good condition.

Jusy hoping it will rain soon to see if the caps solve the problem - wishful thinking!!

 

[bobasd]

OP,
you've been advised how to deal with your difficulties - there are no easier ways.

 

[mr_chaela]

Had a closer look at this today, removed skirting and lifted screed in hearth area.

The DPC in the wall is at FFL. The DPM in the floor is a black fibrous mat 2-3mm thick about 20mm below this. The floor screed is 20mm thick, it is black, not concrete, so presumably self levelling compound.
Whoever removed the chimney breast filled the hearth with concrete up to the floor DPM, then plastered the wall bridging the walls DPC. they then finished off with a 20mm cement screed with no DPM underneath.

I plan to remove the plaster and treat the wall as per bobasd's recommendation which just leaves the floor to deal with. Can I just synthaprufe the hearth area and fill with self levelling compound. Also can I pour the self leveling in 2 layers.