Damp Chimney Treatment

I have recently moved house. The chimney breast has been dry lined and so is completely non-operative. Recently large damp patches have occurred, though there hasn’t been any rain. It doesn’t look like it is coming from the chimney stack – could it be a leaking pipe? The property is usually left with the windows open a bit so do not think it is condensation. Any suggestions or comments would be greatly appreciated – Paul, Stratford

Hi Paul

Ok this is quite a common problem associated with chimney breasts and can be a real pain.

A damp chimney usually happens for one or more of the following reasons:

  • Water entering uncapped chimney pots
  • Water entering through defective lead flashings around the chimney stack
  • Leaking adjacent rainwater goods
  • Salt contamination of the wall plaster

The first thing to do is to check outside. Try to inspect the chimney and the associated lead flashings. You may well be able to see any defects clearly from the ground but if not you may need access equipment. If you are not confident about doing this yourself then contact your local building surveyor and for a fee they will undertake a survey for you.

Lets deal with the possible causes of the damp chimney breast one at a time:

Water entering uncapped chimney pots

If you suspect water is entering through an uncapped chimney pot then you may need to buy a suitable chimney pot cowl (like a hat for the pot) and install it or commission a builder to do it. However, even if this is a remedy for the cause you may still need to deal with the issue of residual moisture which I will cover further on.

Water entering through defective lead flashings around the chimney stack

Lead flashings are installed at the junctions between your chimney and the roof and are dressed into the brickwork and over the first tile to prevent water getting in. If following your inspection/survey you find that your lead flashings require some attention you will need to employ a building/roofing contractor to undertake the necessary repair works. Again residual moisture resulting from the problem needs to be considered.

Leaking adjacent rainwater goods

Newton damp proof membranes are ideal for treating damp problems

An external inspection carried out by yourself or a surveyor should easily pick up any defects with your rainwater goods. If you find that the defect on the guttering, downpipes etc is directly adjacent to the damp patch on your chimney breast then you may well have found the problem. Now it’s a case of getting the defective rainwater goods repaired or replaced.

Salt contamination of the wall plaster

Salt contamination especially in older chimney breasts is a common problem. The salt contamination is usually a result of fossil fuels like coal being burnt in the fire place. Because coal comes from the ground it can contain salt minerals like nitrates, chlorides, sulphates etc. When the coal is burnt these salts manifest themselves in the brickwork of the fireplace. Over a period of time and especially if the fireplace is no longer used as such the salts can migrate from the brickwork and settle in the wall plaster. These salts then become what is technically known as hygroscopic, which means that they can attract and hold atmospheric moisture from the surrounding environment. This is why damp patches associated with salt contamination are often worse when the weather is. If it is salt contamination there are a few ways it can be dealt with. If a damp patch is small and isolated I have known a very simple and effective solution to work which is certainly worth trying. That is to apply a couple of coats of an aluminium wood primer over the patch. In some cases this can act as a cheap but effective sealant.

If this does not work then more drastic measures may be necessary. You can remove the areas of defective plaster and then re-plaster the wall incorporating a salt retardant additive and sulphate resistant cement in the plaster mix. Having said that patching plaster like this can be a difficult thing to blend and hide in that it can shrink and crack and may require fairly regular attention.

Permanent treatment with damp proof membranes

A very effective solution to this problem is to apply a cavity membrane to the chimney breast. Cavity membranes are essentially plastic membranes which are moulded in a stud pattern much like an egg box is. The membrane is applied to the chimney breast either over the existing plaster or after plaster has been removed. The membrane is fixed into position using special ‘mushroom’ fixings and the surface of the membrane has a mesh on it in order that a new plaster finish or ‘dab fixed’ plasterboard can be applied. What it achieves is an effective and permanent solution to your damp walls and any salt contamination because the membrane does not allow moisture or any of the harmful salts to reach the wall finishes. These membranes will also deal with the problem of residual moisture after an external problem has been rectified. Often damp walls will take up to a month per inch of their thickness to dry once a moisture source has been removed. As they dry the residual moisture can show itself as damp staining, salting, blown plaster, peeling surfaces etc. so if you apply a cavity membrane to the problem areas you can forget about any of these detrimental affects because they are completely impervious to dampness and the associated salts.

The first form of cavity membrane was introduced by John Newton & Co in 1937. These days we are still a leading provider of damp proofing membranes and Newton 803 Newtonite and Newton 805 Newlath are ideal for this type of installation.

Do e-mail me directly if I can be of any further assistance

Toby Champion

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This entry was posted in Advice • May 6th, 2010 • Back To Top

25 Responses to “Damp Chimney Treatment”

  1. lionel binns says:

    Hi

    I run a property maintenance business and have recently been asked to look at a chimney breast in a converted attic. The chimney was plastered at the time of the conversion and is showing damp patches which get worst as the weather gets damper. They have chiney pointed and flashings seen to by a roofer Ive suggested it could be condensation forming at the top of the chimey and that salts in the mortar are transfering moisture to the plaster. Ive seen the mesh membrane on various forums and have a couple of questions, 1. external angles of chimey breast? plastis beads? 2. Once youve applied mesh and plastered it over what happens to the damp on the chimey breast, mould spores? Condensation? I would appreciate your comments so I can reassure the customer
    Regards Lionel Binns

  2. lionel binns says:

    Hi

    I run a property maintenance business and have recently been asked to look at a chimney breast in a converted attic. The chimney was plastered at the time of the conversion and is showing damp patches which get worst as the weather gets damper. They have chiney pointed and flashings seen to by a roofer Ive suggested it could be condensation forming at the top of the chimey and that salts in the mortar are transfering moisture to the plaster. Ive seen the mesh membrane on various forums and have a couple of questions, 1. external angles of chimey breast? plastis beads? 2. Once youve applied mesh and plastered it over what happens to the damp on the chimey breast, mould spores? Condensation? I would appreciate your comments so I can reassure the customer
    Regards Lionel Binns

  3. jenny delfino says:

    i have an ongoing problem with 2 chimney brests showing large dark damp patches after long heavy rainfall…stacks are capped and were rerendered and flashings renewed 3 years ago but the problem has never been solved and seems to be getting worse…it feels sticky to touch after days of heavy rain…..vents are permantently removed to allow plenty of ventellation (also vented on the exterior) brickwork inside of chimney does’nt feel damp…worst area affected where top of brest meets the ceiling and around the vent holes…..whats your advice and i’m also interest in your reply to lionel regarding mould spores condensation and ventillation when lined with membranes ..regards jenny delfino

  4. jenny delfino says:

    i have an ongoing problem with 2 chimney brests showing large dark damp patches after long heavy rainfall…stacks are capped and were rerendered and flashings renewed 3 years ago but the problem has never been solved and seems to be getting worse…it feels sticky to touch after days of heavy rain…..vents are permantently removed to allow plenty of ventellation (also vented on the exterior) brickwork inside of chimney does’nt feel damp…worst area affected where top of brest meets the ceiling and around the vent holes…..whats your advice and i’m also interest in your reply to lionel regarding mould spores condensation and ventillation when lined with membranes ..regards jenny delfino

  5. Lucinda Muschialli says:

    Thank you Jenny for your query, I have forwarded it to Toby Champion who will contact you directly

    Lucinda

  6. Lucinda Muschialli says:

    Thank you Jenny for your query, I have forwarded it to Toby Champion who will contact you directly

    Lucinda

  7. pen says:

    I have large damp patches sporadically all over the upper part of a chimney breast. The downstairs section has gone rusty where the metal edges of the plasterwork are… There has been a lot of rainfall recently but the flashings were replaced with zinc 12 years ago and the chimney pot removed … Any ideas?

    • Lucinda Muschialli says:

      Hi Pen

      Thanks for your enquiry, it’s difficult to diagnose without viewing. Chimney areas are notorious for damp problems which are usually linked to poor quality detailing with the build. If you are noting signs of dampness after significant rainfall it points to either a failure in the pointing near the chimney or the installation of the flashing. You will find salts residue if this is the case after the damp ingress issues are diagnosed and cured. We have meshed membranes such as our 803 Mesh

      This will offer a permanent barrier and will allow for the walls to breathe without pushing dampness elsewhere but still the source of the ingress should be fixed first.

      If you have any questions or would like to talk to us about the situation further please call us on 01732 36 0095

      • pen says:

        Thanks for your reply. If you send me details about your product, I will let my builder know about it. I got the chimney repointed etc, but am now dealing with another much older damp problem.. This is what the builder is planning to do

        kitchen / damp wall / Internal.

        Chop off old damp decayed plaster approx 2m sq. On staircase wall.

        Paint the wall with blackjack, (NB but this has already been done once…)

        Sand and cement render and plaster skim,

        What do you reckon to that?

        Your help much appreciated.

  8. Lucinda Muschialli says:

    Ok it seems the blackjack may have held it back for a period but has broken down. Unless you can get back to the fabric , applied systems are only as good as the background they are going onto. We recommend cementitious products like our 101F for these type of projects but the black jack may be very difficult to remove. Either go down the route your builder has but understand the above and know that when you hold damp back you can move it to other areas or utilise a membrane see attached link showing how the product would work in your circumstance to give you an idea on price 10sq metres of the product is £80.00 and the plugs cost £32. Installation instructions are http://newton-membranes.co.uk/wp-content/uploads/2011/05/Installation-instructions-803-Newtonite_Mar11.pdf

    If you need any further assistance please give us a ring

  9. Jim Goffey says:

    Hello!
    Having (hopefully) dealt with the exterior problems with our chimney stack I need to replace defective plaster in the attic rooms and would like quotes from a local installer to use your damp proof membrane. Can you give me contact details for a North Liverpool/SW Lancashire based supplier?
    Many thanks.
    JG

    • Lucinda Muschialli says:

      Hi Jim – many thanks for your comment, we will e-mail you a list of installers for the area you specified directly

      Best wishes

      Lucinda

      • Jim Goffey says:

        Hello Linda, thanks for your swift reply (which I’ve only just been able to access). If you did manage to get a list off to me can I trouble you to resend? Would be much appreciated since I need to get this job done ASAP. Thank you. JG

  10. Jez says:

    Hi,
    Just moved into a house where the disused chimney which does not have access through the roof (stops in the eves circa 1970) has damp patches (almost feels slimy rather than wet) We’re really confused because on checking the chimney stack in the eves the brickwork is bone dry. (no leaky pipes etc) Infact in my daughters room (where the chimney breast is, all other walls are dry. Any ideas would be gratefully received. Have resubmitted this comment as my email address was incorrect

    Jes

    • Lucinda Muschialli says:

      Hi Jez

      Thank you for your enquiry. Chimney breasts often have problems with dampness especially when they have been unused for some time. Here is a link to our on-line article, where you should find all the information you need regarding chimney breasts, the associated damp problems and suggested remedies: http://newton-membranes.co.uk/news/advice/damp-chimney-treatment/

      Once you have read the article you may wish to visit our on-line shop where you will find our damp proofing packs that can be installed by the competent DIY’er or Local builder: http://newton-membranes.co.uk/store/

      I hope that this information is helpful but if you require any further information or advise, please do not hesitate to contact our technical department on: info@newton-membranes.co.uk

  11. cathey says:

    Hello, I live in a victorian terrace, 2 up, 2 down style with a fireplaces in all 4 rooms that all go to a central chimney stack. The fireplaces have been blocked (with fibreglass). In the recent storms loads of rain came down the chimney and leaked into the loft and top bedroom. I’ve had a roofer round who’s done what he can from the outside, but my concern is that the loft is still wet (even though it hasn’t rained for a day). I’m going to get the fireplaces unblocked to air the chimney. What else could I do to get the existing water out of the loft? I’m worried about the joists. Many thanks… good website and article

    • Lucinda Muschialli says:

      Hi Cathey
      Thank you for the enquiry. Has the chimney been capped as part of the outside works? If you have done everything you can from the outside then I would suggest the dampness in the loft may just be residual. To help the drying out process you may want to put a heater or dehumidifier into the loft space to help reduce excess moisture which may help. The joists should recover if they have only had limited and short exposure to the damp. If you are really worried then it may be prudent to get a specialist damp proofing company in to inspect the area although it is likely that they will charge for doing so.

      I hope that this information helps.

      Kind regards

      Toby Champion
      tobychampion@newton-membranes.co.uk

    • H.A.Ross says:

      The problem is that all chimneys were made to have fires in them and I experienced the same problems with my chimneys so fitted 3 wood burning stoves and they soon dry up any dampness. If I light the one downstairs then you can put your hand on the wall upstairs and it feels really warm. A close neighbour had the same problem but he removed his chimneys altogether. I did have my chimney first lined with Newton membrane to prevent any further ingress of water.

  12. Jess says:

    Hi,

    recently bought my first property, when the survey was done wardrobes in the main bedroom covered a damp patch approx. 20cm from the skirting board and 1.5m across. The wall used to house a chimney breast which was been removed 15 years+ prior.

    We think the party wall may have a chimney still in use (or at least in place if not used). And this is causing rising damp. Do you think this could be the reason for the damp patch?
    Who is liable for any works needed to be taken out? us or the neighbours?

    Look forward to hearing back,
    Thanks Jess

    • Lucinda Muschialli says:

      Hi Jess

      Thank you for your enquiry. Chimney breasts often have problems with dampness especially when they have been unused for some time. Here is a link to our on-line article, where you should find all the information you need regarding chimney breasts, the associated damp problems and suggested remedies: http://newton-membranes.co.uk/news/advice/damp-chimney-treatment/

      Once you have read the article you may wish to visit our on-line shop where you will find our damp proofing packs that can be installed by the competent DIY’er or Local builder: http://newton-membranes.co.uk/store/

      I would have thought that you would be responsible for anything that was occurring on your side of the wall.
      I hope that this information is helpful but if you require any further information or advise, please do not hesitate to contact our technical department on: info@newton-membranes.co.uk

      Kind regards

      Toby Champion
      tobychampion@newton-membranes.co.uk

  13. Christine Leach says:

    We have a case of chimney damp on the upstairs chimney breast. A specialist company have recommended taking the plaster off, putting a membrane in and replastering. They have quoted £1800 which seems expensive. Just wondering if this is realistic.

    We’d also like to try aluminium wood primer first but not sure what we are buying or where to get it from so advice would be appreciated.

    Regards,

    Christine Leach

    • Lucinda Muschialli says:

      Hi Christine

      Thank you for your enquiry below. We would recommend that the plaster is removed before the membrane system is installed, however we would not be able to comment on the cost you have been quoted as we are suppliers, but we do have specialist installers if you wish to get further installation quotes. An aluminium wood primer acts as a sealant for damp patches however it may not be 100% effective but can be a cheap solution if it works. This product is widely available but there are no particular ones we recommend.

      In the meantime I have included here a link to our website article on damp chimneys which may help in particular the section regarding salt contamination. http://newton-membranes.co.uk/news/advice/damp-chimney-treatment/

      Should you wish to undertake the damp proofing on a DIY basis or if you intend to employ a general builder to undertake the work then our damp proofing packs and other damp proofing products like our condensation paint and external water repellent can be found on our website here http://newton-membranes.co.uk/store/

      I hope that this information helps and if you would like me to recommend or send a list of your local Newton approved contractors please let me know or Request List of Damproofing and waterproofing contractors on our website. In the meantime you can find our damp proofing brochure and our guide to damp proofing damp walls here http://newton-membranes.co.uk/download-technical-information/

      Kind regards

      Aimee Boyle
      Technical
      aimeeboyle@newton.membranes.co.uk

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