Have you got a damp stain on your chimney that you can’t seem to get rid of?

Is it hygroscopic salts?

Is it a leak?

We have seen many cases where roofs have been repaired around chimneys a number of times and the other roofer-builder has said the other Company didn’t do the lead work correctly, roof repairs, chimney repairs, or the pointing etc etc and then they still have a damp stain on the internal chimney breast.

Recently I went to carry out a damp survey in Wiltshire, they had literally given up, and this is how the story goes……. My client purchased a property 6 years ago, it was noted by the surveyor before purchase that the internal chimney breast had staining and the chimney probably needed small pointing works, and further investigation was necessary. This work was carried out after they purchased the property in the summer and was decorated, a few months later on in the year the damp stains on the chimney breast came back, this time it was worse than before. So they called the roofer back in, he checked the chimney and tested it with a hose pipe and couldn’t see any problems, and he disappeared very quickly…….. They then called another roofer-builder, this guy pulls around on the lead flashing and seems to think the chase isn’t deep enough and also it needs a new roof,  tells the client this is what needs doing, orders the scaffold and off we go again! The damp patch on the chimney seems to slowly shrink and disappear over the next few months, then its back again……… by this time my client said they couldn’t believe it. They then called the roofer out again and explained that the damp stain is back! He couldn’t find the cause and he disappeared very quickly like the last guy.

Next comes the roofer with the all singing and dancing website, more professional, and more knowledgable,  and he seems to think the chimney needs to be simply taken down and capped over with some ventilation. Seems like a good sensible idea they think……….A couple of weeks later the scaffold lorry turns up, up goes the scaffolding, up goes the roofers, down comes the chimney, this is then all capped off, vented and pointed and looks like a brilliant  job. The damp patch doesn’t go and the roofer can’t seem to find the cause….same old story!

You can imagine what my client was thinking now. By this time they had given up and thought they would have to put up with it. They then get some rising damp problems and contact a couple of damp proofers to come and carry out a survey, I then come along and have a chat about the high ground level causing the damp problem at the front, whilst looking at the front I said, “I see you’ve had a new roof then”, and bang….I get hit with it.  And I said “thats probably salt damp” “Whats that” my client said, I then showed them a couple of case studies I had on damp chimneys. That was the Eureka moment for them. I went one better than that though, I showed them the damp patch grow, and to do this I use a humidifier, this can produce high relative humidity very quickly, give it 5-10 minutes you can see the damp patches grow. The below pictures show the humidifier in action raising the relative humidity of the room to show the hygroscopic salt damp patch growing.

This is before I raised the relative humidity.



This is after , you can see the hygroscopic salts on the chimney breast now (damp looking patch at the top of the chimney breast), also notice the vertical profile up the wall, following BRE Digest 245.


DSC06333   A picture in picture thermal image showing the dampness, note the holes are warm still from the drilling of the mortar samples.


This thermal image shows a quite a large level compared to the bottom thermal image


The below thermal image shows a difference in temperature between Sp1 and Sp2 being .3 degrees, this shows how powerful thermal imaging can be using temperature differences. My client now was convinced that the problem could be solved after spending literally thousands of pounds for nothing. All results were carried out to BRE Digest 245 methodology giving us quantitative results and the client complete peace of mind.


 BRE Digest 245 methodology results


Picture 1 shows after the sample has been filtered with a filter paper and de-ionised water.

Picture 2  shows that Nitrates and Chlorides are present

Salts analysis matched with the drilled profile and visible salt damp staining, this confirmed hygroscopic salts from long term burning of fossil fuels, and no free moisture which means that there is no leak in the roof or around the chimney and probably never was.

Can a damp meter be used to tell you exactly what is going on?


Using a damp meter to test for hygroscopic salts and free moisture  especially around a chimney will not tell you what the problem is, the damp meter can’t differentiate between free moisture and salts.

I often get asked the percent of chimney damp problems issues that is solely related to hygroscopic salts only. In about 75% of my surveys free moisture is present from penetrating damp, and or rising damp at the base of the wall.

Please click on the below two links that also show other chimney damp causes.

The below link is of an interesting survey again relating to a damp chimney issue.


The below link shows another interesting survey, again eating to chimney damp issues. This survey show another issue where we used data loggers to help diagnose the issues.


Below is a time lapse video of salt damp

Below is the before and after pictures of the time lapse showing the salt damp on where a chimney used to be in a property in Trowbridge Wiltshire.

Note the dampness on the wall in the below picture, this is hygroscopic salts absorbing moisture from the air that has been made humid by the humidifier


Contact Complete Preservation of Trowbridge Wiltshire for advice, or to book in a survey, we offer site surveys up to a 3 hour drive.

I’m often asked is it likely to be hygroscopic salt damp or just free moisture…..it is impossible to tell using a damp meter and even I find that sometimes I get it wrong without the gravimetric sampling data.

We also offer a service where you can post your plaster sample to us for us to test using the laboratory methodology in BRE Digest 245, we can then tell you if the sample has any free moisture, and or hygroscopic salts present. If you wish to have this carried out please contact the office and I can advise you on the necessary steps.

Each sample costs £60.00 including vat.

We also offer chimney aerial surveys , to look for defects like lead flashing detailing, pointing defects etc. These aerial pictures along with the data collected, help us to ensure we offer correct diagnosis. Complete Preservation can carry out the survey and all the necessary remedial works for chimney defects and all internal works to the walls where needed.



Our main website is www.completepreservation.co.uk

We can be contacted to arrange a survey on 01225 769215  

Posted by Complete Preservation


  1. The above sounds exactly like our situation.
    I feel relief in this is most probably our problem, we have spent over £6000.00 on our chimney, flashing and roof which we couldn’t afford. I can’ t believe that all of these people that looked at our property didn’t know this hygroscopic salt could be the problem. Can you carry out a survey for us please?
    Thanks for making the effort and taking the time to produce an excellent description of the problems with videos, I’m sure many people have and will benefit from this.


    1. Hi Mark

      Thanks for your kind comments.
      You can contact me on enquiries@completepreservation.co.uk and we can discuss further


      1. My box room chimney breast and side walls get very damp. I called in the so called Damp Experts to sort out the problem which cost me a lot of money.
        Unfortunately, none of these 3 men managed to solve the damp problem and I am back to square one.
        Please, help.
        The first man replaced the lead flashings ,soakers and renewed flaunching.
        The second expert put cowling
        The third guy repointed the chimney .
        I simply do not trust them now. Each new one comes out with a different story. They want your money disappear very quickly.

      2. Hi Ray,

        Where is the property?

  2. Great post, really helpful. So what did these people do? Have the plaster removed and replaced with a different type? Thanks


    1. Hi Stewart,

      Yes, but it is important to make sure it is just hygroscopic salt damp first of all.


  3. My wife & I moved into an old 1926 build in April this year, we have had a new DPC inside & out. All walls & ceilings replastered, new doors & windows, a new roof & bathrooms etc… We still have a damp chimney breast despite new lead flashing, repointing, cowl & render, yet the damp patches remain…
    I can email you an image but require an address.


  4. Have replied, sorry for delay, I had not seen your reply.


  5. If it is caused by salts in the chimney stack – How do you remove the salts then ?


    1. Hi Angela, you can’t remove the salts unfortunately.


  6. The problem I have is that – I have damp on both sides of the chimney stack – above the skirting board approx 12inch x 12 inch. I have removed the skirting board – and the bricks arent damp at floor level – so not rising damp.

    The chimney is open in the room and vents into the loft as well as having an air brick at the top venting to the outside.
    I have checked every for a leak in the tiles, the beams are exposed and can see no signs of water ingres.

    So all thats left is that possibly there is a leak from the tiles directly above where the chimney is – in the loft or there is condensation – warm air rising up inside the chimney is condensing and producing water. Although it is vented – the draw is not that great.

    If you have any ideas – please shout as for the life of I’m at my wits end …..


    1. Hi Angela, it’s possibly salts or rising damp, there only needs to be a small amount of moisture at the base to cause staining -spoiling. Many old properties also have a hearth that is in direct contact with the earth floor, possibly bridging any damp proof course, these are very well known issues. You could instruct a surveyor, or if in doubt you could send some samples in to be checked if you wish


  7. I think it’s definitely salts – as after a week or so – there is a crumbly fluff (technical term…) left on the wall . I’m just waiting until we have a good downpour to see if then gets wetter.
    Previously there were 2 adults and a child staying in the bedroom – with the heating on, so (possibly) condensation is an issue ?

    Pity I cant post a picture on here


  8. Mary Williams June 24, 2016 at 10:05


    You fixed our friends damp chimney on there house a couple of years back, they had previously spent a small fortune before you got involved. It would be wise for us to instruct you to carry out a investigation to find out the actual cause please. How can we arrange something?


    1. Hi Mary,
      A safe option is a detailed survey, please email me on enquiries@completepreservation.co.uk with you details.


  9. […] The below link is of another interesting survey regarding a damp chimney https://blog.completepreservation.co.uk/2014/06/02/the-damp-stains-on-the-chimney-breast-is-it-salt-… […]


  10. Hello l. I have the same problem, if salts are the cause is the problem solvable ?


    1. Hi Carl, there are various methods available depending on the the problem area. I find most contractors, or surveyors offer different solutions.


  11. Excellent article on this issue, thanks. I would appreciate if we can put a date together, on the understanding that you could carry out an investigation on my issues I have. I have had various people look at this damp issue over the last few months with completely differing views.
    The property is in Chippenham Wiltshire, it is three storey and damp is on every floor.


    1. Hi Ted, thanks for the kind comments first of all 🙂
      Give me a ring next week and we can discuss in detail.
      Chippenham is pretty local compared to some of the distances I travel looking at this sort of thing.


  12. Over the past 25 years, I have paid for many builders to rectify a damp patch immediately right of a chimney breast on the top floor of my Victorian cottage. Three years ago builders replaced the chimney, roof flashings and suspect roof tiles, rendered the whole outside wall, used a sealant on one upstairs internal main chimney breast and replastered the secondary chimney breast and ceiling – and they left with the recommendation that I used a de-humidifier to dry out the rooms.

    Having found this blog, at last I understand how, naturally, the damp continues to expand and so I ask that Complete Preservation can recommend builders with integrity, who have inwardly digested all that you write about and who work in the area of Hampton Court.

    I feel encouraged to have found this site.



  13. Wendy Robertson December 1, 2020 at 14:36

    Hi, this article was really useful thanks. I have a damp stain on an internal chimney breast and have had 2 roofers make sure the chimney is in good condition and not letting water in. I’m now wondering if salts are causing the problem. However I live in the NW near Chester. Could you recommend anyone in this area who could take a look? Thank you


    1. Hi Wendy, you could send a sample if you wish to get tested


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