We often get asked to survey for damp issues regarding chimneys, chimney breasts or adjacent areas. It is impossible to say exactly what the issue is without taking plaster/mortar samples. This is because there simply can be various dampness issues that we can’t differentiate between on a visual survey along with just a damp meter, and other equipment.
Long term burning of fossil fuels, can lead to aggressive hygroscopic salts that stain the plaster, and can then fool a layperson to think there is a damp issue possibly because of penetrating or rising damp etc. Often we get called in when our clients have spent several thousand pounds trying to fix the damp chimney issues, and problems still persist. Please read the case studies below relating to slightly different damp stained chimney issues, these can give you an understanding of how we carry out surveys, and the detailed moisture and hygroscopic salt analysis following the laboratory methodology in BRE Digest 245.
Case study one
Where we survey and repair many chimneys we come across lots of different situations, and hear so many different stories of mis-diagnosed repairs.
This one just shows how confusing it can be for the layman……….Old listed building which has had many damp issues over the years, and it would seem the previous damp diagnosis was poor to say the least. Anyway the owner of this building contacted us because they have damp stains and water running down the walls when it rains, but not all the time! The chimney has been re-built by a local builder after he diagnosed penetrating dampness as the sole cause of the damp issues , and said a chimney re-build would fix it using lime mortar.
During the works, and after the works the same problem continued just like it used to, unfortunately he didn’t want to help anymore as he had been paid, and he’s off to the next damp chimney repair.
During my initial phone call it was discussed how when diagnosing dampness issues it’s like a jigsaw puzzle fitting all the pieces together and voila there you have it…….the most important piece of the jigsaw puzzle is the testing of the samples of plaster/mortar, this is done following the laboratory methodology in BRE Digest 245. This basically means the plaster sample is analysed in our laboratory to see if any free moisture is present, and if there are any hygroscopic salts present and the amount, and type.
The survey
The property was occupied and is a small school with many little children all producing lot’s of moisture. Ventilation of the property isn’t ideal, and the relative humidity at the time of inspection was 75% @ 19.5 ºc. This is very high at that temperature!
The chimney wall is of solid brick construction with a painted finish internally along with the front wall where there are also very similar visual issues, the wall at lower level was panelled potentially masking any dampness issues.
The visual appearance is patchy stains and on close inspection it appears that there is visible damp. The weather was dry during the inspection and also for a number of days prior the inspection.
By inspecting the wall with our calibrated Flir T600 thermal imaging camera we can check for any hidden anomalies, and also calculate dew points for condensation, to see if this is a possible cause. This is done by meterlink with our Flir MR77, which measures the internal atmospheric conditions.
Condensation wasn’t occurring, and all surfaces were significantly above dew point……no risk at that specific time.
Where we specialise in these issues the cause is apparent to me, but we still have to go thorough the process of elimination to ensure correct diagnosis.
The problem is hygroscopic/deliquescent salts derived from long term burning of fossil fuels in the chimney; these salts have migrated from the chimney to the adjacent areas. Hygroscopic salts absorb moisture from the air; a good example is that of sodium chloride, common salt, which under humid conditions crystals become ‘sticky‘ and clump together. However, there is an extreme of hygroscopic-deliquescent-where the salts absorb so much water that affectively they dissolve in themselves and thus we have a solution. The point at which deliquescent occurs depends on the particular salt. For example common salt is hygroscopic at 75% relative humidity but increased this to 85% plus and keep it there then it becomes deliquescent and therefore liquid. Once in liquid form the salts become mobile and can move away from their point of origin.
Difference salts become deliquescent at different humidities. Some like calcium chloride and many of the calcium salts deliquesce at very low humidities: others such as sodium chloride become deliquescent at much higher humidities. Whatever the case there are occasionally conditions where the wall or material becomes physically damp solely due to the contamination by such salts.
This shows why the wall in question was presumed to be wet because of penetrating damp when it rains, however before it rains it can become quite muggy and this often slight adjustment (higher) in relative humidity is enough to tip the balance.
Case study two
Complete Preservation are specialists when it comes to chimney dampness investigations, when I say this it’s because it’s what we do every week. We follow surveyors,damp specialists, roofers, builders, the lot.
Chimney dampness is very difficult to get right, you speak to a roofer they say it’s a leak, you speak to a builder, they say it’s a leak, you speak to some damp specialists and they may think they know the correct diagnosis………There is never any proper analysis carried out, it’s just presuming. Well this had lots of presuming just like the others I visit on a weekly basis where they have often spent thousands of pounds and they still have issues.
Below is some pictures of a recent survey, this property has had everything done to it to try and fix the damp issue on the chimney and adjacent walls. The external gable wall has been re-pointed, it had been waterproofed with an external waterproofing product, chimney has been ventilated, ventilation has then been sealed up, specialist salt resistant re-plastering has also been carried out internally……and there is still damp patches on the chimney breast which get worse in the winter months.
Damp problems on chimney breasts are a completely different kettle of fish when it comes to diagnosis, there is no way possible that you can actually diagnose if there is a small amount of free moisture in the wall with a damp meter, damp meters generally measure resistance, 1.5 % of hygroscopic moisture content if hygroscopic salts are present even if the wall is bone dry will give a reading on my protimeter of around 25 wme (wood moisture equivalent), this is considered a high reading, or should we say something is going on to make it read this figure. So we get 25 wme on our damp meter is this hygroscopic salt or damp from penetrating damp? It’s impossible to say. Some independent damp specialists I have even known to use a speedy meter, also known as a carbide meter, these are an absolute complete waste of time to diagnose any kind of damp on site when there is potentially hygroscopic salts in the sample on site. This is because they can’t differentiate between free moisture (damp) and hygroscopic salts, when the pressure goes up in the speedy meter it will only tell you the total moisture content, this being the sum of the free moisture and hygroscopic moisture content. This is well documented in BRE DIGEST 245, THESE SPEEDY METERS CAN’T DIAGNOSE RISING DAMP OR ANY DAMP WHEN THERE IS POTENTIALLY HYGROSCOPIC SALTS PRESENT IN THE SAMPLE ON SITE.
The only way to tell if there is free moisture in the sample is to follow the laboratory methodology in BRE DIGEST 245, this will seperate the free moisture and hygroscopic moisture content. This involves laboratory analysis, we carry this out using excel spreadsheets to produce the results which we then put in a table of results indicating where the sample was taken.
In the below picture you can see the damp patch – stain on the chimney breast and the adjacent wall. Readings from between 24% wme to 54% wme were taken across the damp stains. Damp staining was noted at ceiling level all the way across the gable wall, and the rest of the breast at lower level just gave the readings you would expect from a dry wall.
It is also an advantage to carry out an aerial view of the chimney looking for any obvious defects. Note the re-pointing that has been carried out.
This is the view of the chimney in the roof and the gable wall, there is clear dark staining to the breast.
A data logger was installed along with a T probe to measure the surface temperature of the breast, a data logger was also put in the roof to measure the relative humidity, air temperature, dew point and vapour pressure.
The bottom picture in the image shows that the surface temperature was only 3.5 degrees above dew point.
Just for my own research I installed a data logger up the chimney to take readings, this was on my my telescopic carp rod…..luckily I wasn’t off fishing 🙂
Data loggers were placed around the property where I thought necessary, and most importantly an external data logger, this is all then downloaded after a couple of weeks and put into a specialist excel spreadsheet, we can then make many graphs. One point I will make, if you don’t use a surface temperature logger you can’t prove the surface has gone into condensation, you also need an external data logger to show the differential vapour pressure between external and the internal environment, this being the internal vapour pressure is the sum of the external vapour pressure and the internal vapour pressure.
72,000 measurements were taken with our data loggers, this may sound ridiculous but it’s easy, the loggers we have programmed to take a reading every half an hour. Data is king, using this data we can now produce many graphs in our excel spreadsheets, for this survey I produced 12 graphs, some of which isn’t necessary but it gives me a better understanding of how moisture moves through the building.
The below graph shows the temperature, dew point, and relative humidity of inside the chimney.
The below graph is the game changer this actually shows the surface temperature and dew point meeting, this proves the chimney hits dew point in the roof, and condensation is occurring on the chimney breast.
Below is the table of results, as there were many samples taken I have only shown the samples which were wet, all the others were dry.
The samples taken were near the surface of the lime mortar joint, and also deeper into the wall by inserting a 10mm tube, this ensured there was no contamination of sample drillings that could make surface samples appear the same as samples taken within the wall. Free moisture was found in surface samples but not at depth indicating along with our graphs the issue was condensation forming on the chimney breast, this then subsequently ran down the wall and contaminated the chimney in the bedroom and adjacent walls. We now know the cause of the issue, I could then write a specification of repair to include mechanical ventilation to ensure this problem will not come back.
Case study three
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, 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….. 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 Dropbox. That was the Eureka moment for them. I went one better than that though, I showed them the damp patch grow, 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, BRE Digest 245.
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 laboratory 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. I obviously can’t conclude that there never was a leak.
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.
Case study four
The two below pictures show a small amount of yellow ponding on the hearth of the chimney. We were called into this property to find the cause as everybody has was just having a guess. This is actually deliquescent salts from long term burning off fossil fuels. On the day of the survey the humidity was very high and it become deliquescent right in front of me, and this also occurred on another chimney in the house but not to this extent. You can see the sample pot on th hearth that I removed which had extremely high levels of chloride, nitrate and ammonium…..typical of very long term hygroscopic and deliquescent chimney salt issues.
Case study five
A few years ago hardly anybody knew anything about hygroscopic salt damp on chimneys, and now every time a chimney has a damp stain / patch on the breast or adjacent ceiling it is often referred to as hygroscopic salt damp
What amuses me is that even with my experience with chimney damp sampling over many years I still couldn’t tell why a chimney is damp without taking samples.
What i’m finding now is that it’s gone full circle, surveyors just assume its hygroscopic salts rather than possibly penetrating damp, or both. Works proceed by replacing the damp plaster etc, and the damp comes back…..This might not be because the hygroscopic salts have migrated through the plaster, it’s probably because there is still a penetrating damp issues. I only highlight this because this is what I continually see now.
Top tip
You need to ask the surveyor inspecting your chimney as to why it is damp. Ask them how they have come to the conclusion. Make sure samples are taken, and analysis is carried out. This can be carried out following the laboratory methodology in BRE DIGEST 245. It is also prudent to make sure an aerial survey is carried out using a camera pole, to check for external defects. Personally I would never inspect a chimney without an aerial survey, gravimetric sampling, and thermal imaging. We can also listen to the chimney with our digital acoustic equipment whilst its being sprayed down for any dripping noises.
If you need help with getting the correct diagnosis in regards to your damp chimney give us a shout.
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