Damp - Chimneys

Damp patches on chimney breast

Q I have damp patches appearing on the chimney breast in my bedroom. These are towards the ceiling and occur in times of high humidity and rain. However during an excessively heavy downpour in summer (3" in 3 hours) no damp patches. The chimney has had "everything" done do it externally: re-pointed, all new flashings, capped and many treatments of waterproof sealant. All the tiles and felt around the chimney have been replaced. Internally there is an air brick for ventilation.

At a loss to know what to fix next?

A What you describe sounds very much like salt contamination as a result of a previous leak or leaks. Have a look at  Article 14 under Informative Articles on this site, which is titled 'What price a correct diagnosis'. I think this describes your problem and it should help explain what is probably happening.


Q Peter, thank you for coming back to me on this. The example in the article sounds a mirror image of my problem! Fortunately I have not had the chimney replaced yet! and the bedroom fireplace is blocked off although the lounge fire, using the same stack, is still in occasional use. If I wanted to have this tested presumably I could use your services. Or maybe just go straight to remedial action and have it replastered?


A It may sound crude but sometimes you are able to test it yourself by 'tasting' the salts with your tongue - if you dare!. Also remove a patch of the affected plaster back to the brick beneath which should be dry and dusty looking. To remedy just remove the salt contaminated plaster and replace, preferably with sand and cement at 4:1 and a skim finish.


 

More - Damp patches on chimney breast

Q We have recently bought a mid terraced property of approx. 100 years old. We have noticed whilst decorating, two damp patches, both on the chimney breast walls in the living room and dining room. The damp patches are no where else.  There is no smell or mould, and the paints not flaking. The house has been previously treated for rising damp (1990's). Before we went away, I felt the walls, and they seemed fairly dry, however having returned from a fortnights holiday, they are damp (but not wet) What could this be and how do I resolve it?


A It sounds very much like hygroscopic salt contamination could be a possible cause. These are present in abundance in a chimney flue where coal has been burnt in the past. If dampness/water entered into the flue at some time in the past it could have dissolved these salts, brought then through to the decorative surface and the moisture evaporated off leaving the salts behind in the decorative finish. During dry low humidity weather the patches will be dry but during damp/high humidity conditions the patches appear. This would continue indefinitely even if the cause of moisture penetration has been rectified.

The other obvious possibility is that water is currently getting into the flue. Have you had the flashings, soakers, flaunching of the chimney stacks checked? This may sound strange but it is sometimes possible to 'taste' the salts if they are present in sufficient quantities. If it is just salt contamination the remedy is to remove the contaminated plaster plus a margin back to the brickwork and make good with a salt retardant mix such as 3:1 sand: cement and skim finish.

 

Q Thank you very much for your response to my question.I'm not sure whether this is something you can help me with but is there a register that I can look at which will assist me in choosing a legitimate company to do the work(s), rather than picking from the yellow pages.  I've also heard that you can have the flues capped, would this help if the problem lies with rainwater entering the flue? Either way, it sounds like I need to have the plaster re-done advisably after I have had the flashing etc. checked? Your advice is much appreciated.

A Hello again
I would suggest that you use a company that is a member of the British Wood Preserving and Damp-proofing Association (BWPDA). They have recently changed their name to Property Care Association (PCA). The PCA has a web site with members listed.

If your flue is no longer used then it should be capped but it should also be ventilated top and bottom to avoid condensation forming in the flue and causing further problems.

 

 

Damp stain next to removed chimney breast

Q I have a damp looking stain either side of a now non-existent chimney breast.  The damp proofing was done about a year ago and the walls were re-plastered under the dado rail.  I then had all the walls skimmed over for decorating about three months ago, but the stain is still coming through.  From reading this site, it would appear that my walls may have hygroscopic salt contamination. Can these stains be covered by a proprietary stain block/spray?


A You do not say if the damp patches are above or below the dado rail. If moisture was present at some time in the area of the original chimney breast then hygroscopic salt contamination is likely. The intensity of visible moisture stain will vary with the weather if this is the case. If you attempt to block the stains you may end up with spalled plaster due to sulphate formation. The only real solution may be to cut out the affected plaster allowing a good margin and replastering with 3:1 sand: cement render and skim finish.

 

 

Dissappearing damp patches

Q I have 2 damp patches in an upstairs room (Victorian House), both are high up the wall (at picture rail height), one on the chimney breast, and one on the wall to the right of the chimney breast. The roof and chimney flashings have been repaired (months ago), and the chimney pot has a cap on it. The external wall has been sealed and redecorated. The damp patches appeared yesterday... and magically, have disappeared today! Can you tell me what on earth is happening, and why? Many, many thanks!


A There are numerous similar questions on this web site about this type of problem. You should read Informative Articles 2, 3, and in particular Article 14 on this web site. What you describe is a typical reaction due to hygroscopic salt contaminated plaster. Such salts are present in a chimney flue as they are a by product of burning coal. When your leaks were occurring the moisture brought the salts in solution through to the surface where they remain since they cannot evaporate off. You have now repaired the leak(s) but the salts remain. So on a damp or humid day the hygroscopic salts will attract moisture and show up as a damp patch. On a dry less humid day they will probably disappear. Does this sound likely? To remedy the problem you will have to remove the contaminated plaster and a safe margin and renew it ideally with a strong sand and cement render and skim finish.

 

Chimney damp

Q Since we moved into our house over 3 years ago we have suffered from 'water ingress' into the first floor bedroom. Subsequently we had the chimney lowered and the roof done as we feared this may have been the cause. Some, but not all of the plaster on the offending chimney breast was hacked off and replaced. Since then, however, it would seem that the plaster has remained wet and stained despite our assertion that the water leak has gone away. The stain manifests itself through the cornice and the ceiling too.

I would be interested in your opinion as to whether you think this is a hygroscopic salts issue caused by the fact that the chimney breast was re-plastered too soon without being allowed to dry properly or whether an application of a primer-sealer type product will help. Would a solution be to hack off the plaster again, allow time to dry and re-apply a lime based plaster?  Would this preclude the use of an emulsion paint finish? Having suffered this stain/wetness problem for many years and having sought many people's advice it has become somewhat of an enigma. Can you advise please??

A There is a strong likelihood that any moisture ingress that has occurred in the vicinity of a chimney will bring with it hygroscopic salts which are abundantly present within the flue as a result of burning coal. You do not state a time scale of the events so it is difficult to advise with any certainty. Read Informative Article 14 on this web site titled 'What price a correct diagnosis?' as it sounds like what you are experiencing may be a similar tale.

It is possible that the new plaster type applied was not suitable to apply onto salt contaminated brickwork and whilst the plaster was wet the salts were able to migrate to the new surface causing ongoing problems. Is the newer plaster as badly affected as the original plaster? Does the intensity of the visible dampness vary subject to weather conditions? The cornice and ceiling plaster are also likely to be salt contaminated.



 

Damp patches on bedroom chimney breast

Q I have damp patches appearing on the chimney breast in my bedroom. These are towards the ceiling and occur in times of high humidity and rain. However during an excessively heavy downpour in summer (3" in 3 hours) no damp patches. The chimney has had "everything" done do it externally: repointed, all new flashings, capped and many treatments of waterproof sealant. All the tiles and felt around the chimney have been replaced. Internally there is an air brick for ventilation. At a loss to know what to fix next?
A It sounds very much like the problem is being caused by hygroscopic salt contamination as a result of a previous leak. Have a look at Informative Articles 2, 3 and in particular Article 14  titled 'What price a correct diagnosis' on this site. It will probably sound very familiar and should help explain what is happening.

 

Chimney damp

Q Since we moved into our house over 3 years ago we have suffered from 'water ingress' into the first floor bedroom. Subsequently we had the chimney lowered and the roof done as we feared this may have been the cause. Some, but not all of the plaster on the offending chimney breast was hacked off and replaced. Since then, however, it would seem that the plaster has remained wet and stained despite our assertion that the water leak has gone away. The stain manifests itself through the cornice and the ceiling too.

I would be interested in your opinion as to whether you think this is a hygroscopic salts issue caused by the fact that the chimney breast was re-plastered too soon without being allowed to dry properly or whether an application of a primer-sealer type product will help. Would a solution be to hack off the plaster again, allow time to dry and re-apply a lime based plaster?  Would this preclude the use of an emulsion paint finish? Having suffered this stain/wetness problem for many years and having sought many people's advice it has become somewhat of an enigma. Can you advise please??

A There is a strong likelihood that any moisture ingress that has occurred in the vicinity of a chimney will bring with it hygroscopic salts which are abundantly present within the flue as a result of burning coal. You do not state a time scale of the events so it is difficult to advise with any certainty. Read Article 12 on our web site titled 'What price a correct diagnosis?' as it sounds like what you are experiencing may be a similar tale.

It is possible that the new plaster type applied was not suitable to apply onto salt contaminated brickwork and whilst the plaster was wet the salts were able to migrate to the new surface causing ongoing problems. Is the newer plaster as badly affected as the original plaster? Does the intensity of the visible dampness vary subject to weather conditions? The cornice and ceiling plaster are also likely to be salt contaminated.



 

Chimney damp - Going mad!

Q I currently have a damp patch on the internal wall of my chimney breast both upstairs and down stairs. I have the plaster hacked off and attempting to dry but the bricks are not drying. I have made house watertight but it seems the bricks are not drying. I have already re plastered once and the damp patch came straight through again, thus why I am attempting it again! Should I replace the damp bricks? Waterproof membranes? Please help as I'm going mad!


A Obviously you are 100% sure that no moisture penetration is occurring and it has been the case for some time. If this is the case then the problem could well be that the bricks are contaminated with hygroscopic salts (moisture attracting) which are a by product of burning coal, as a result of previous leaks. Read Informative Articles 2,3 and in particular 14 on this site which will help you understand what is probably the problem. You need to re-plaster with a waterproof render or slurry to prevent the migration of these salts into the new plaster. Make sure that you allow a generous margin around the contaminated areas.

 
Contact Peter: Email - info@dampdecay.co.uk - Telephone: 015242 71794