Don’t be a drip! Watch out for dodgy damp advice

Carrie

Some caution is required, having not had sight of your building, but some initial comments:

1. Maintaining eaves-level ventilation is absolutely essential if condensation is to be avoided. It will get worse in winter, when the underside of the slates are colder, and you should get vents fitted as soon as possible. This should not be a problem for a competent joiner; round vents which can fit a drilled hole circa 50-75mm diameter are available. Do ensure that they have an integral insect mesh, or you’ll have wasps in the roof before you know it.

2. Try leaving the windows open when you’re in, assuming that you have a toplight or similar, and see if that makes a difference. If it does then ventilation (or lack thereof) is the problem and you could consider having a builder add more vents, if required.

Hope this helps.

A quick Google confirms that white 75mm dia pvc eaves vents are available for the grand sum of £2.790 plus P&P per pack of ten from a well-known online hardware and tool supplier. The joiner would use a hole cutter to form the opening in the soffit (i.e. underside) of the eaves then fit the vent.

Different fixings are required for face-fitted vents in order to prevent water ingress.

Gareth

1. Have you checked the outside of the masonry for any defects which might be leading to either penetrating dampness (for example failure of mortar joints) or localised condensation/cold bridging?

2. Do you know if this is a cavity or solid wall structure?

3. How did you finish the internal walls when you renovated – plaster on the ahrd (type of plaster?), strapping and lining, insulation?

I would be tempted to seek the advice of an RICS building surveyor, if I were you.

Gareth, as I’ve suggested elsewhere why not have a look at the useful Historic Scotland guidance on dampness in historic buildings – I can’t imagine our more severe climate on this side of the border makes the information any less relevant:

http://www.historic-scotland.gov.uk/informguide-damp.pdf‎

If this link doesn’t work for you, use http://www.historic-scotland.gov.uk, click the “learning and resources” tab and in the menu is “free publications”. Click this for a list, and you’ll find “DAMP, Causes and Solutions” (and some other useful-looking guides).
If anyone has a damp problem it pays to do some common-sense investigation first. To help this I’d advise anyone to read both this publication and the earlier SPAB one.
At least you will have some understanding of the possible problem(s) when you involve “experts” and at best they might help you solve the problem yourself.

Never heard of it.

Patented bricks – sounds like the schriver or holland methods – none of which work – research has proven so, and are a complete con.

[This comment has be edited due to breaking our guidelines. Thanks, mods.]

Tess

Rising damp, where it actually exists, is unlikely to extend significantly above ground level – about 200-300mm in my experience, and even that only in extreme cases. I would therefore look for other potential sources such as penetrating dampness from leaking rainwatergoods, open mortar joints, or defective masonry. Condensation is also a possibility.

As for independent advice, the RICS should be able to provide a list of qualified building surveyors in your area. Alternatively look for an architect accredited in conservation under the RIBA and/or AABC schemes (there is a similar system in place in Scotland).

Tess, there is also a useful and unbiased Historic Scotland Inform Guide on dampness in historic properties which might be of assistance to you:

http://www.historic-scotland.gov.uk/informguide-damp.pdf‎

Hi Peter, the link you posted returned a 404 error. I searched on their site but couldn’t see that particular guide.

BW
Tess

Tess, if you look 7 posts up I’ve shown how to find the document, and another that is well worth looking at.

Mods – we dont advertsie anything – we try to steer people in the direction of intelligent and unbiased information that will help them make sensible decisions about not ruining their houses, or losing a lot of money on fraudulent cons.
Dont forget we make no money from our involvement with this forum – all we do is help – we sell nothing – we have an interest in old buildings… If you feel we stand to gain from anything we say or do on this site, please let me know… in the meantime, has the damp industry put pressure on you by any chance?

Cheers

Pete

“…asking people to Google your company. That is a form of advertising …”

That’s an entirely reasonable policy, which I support wholeheartedly in this specific case.

The Terms & Conditions for this website suggest that contributors choose a screen name (pseudonym). It could avoid accusations and work for our moderators if everyone with a commercial involvement was required to do this. Names and company names are far too easy to trace.

Meanwhile back on the topic of dampness, it is evident that condensation is a major problem or contributor to dampness problems in both old and new buildings. Everyone needs to know about condensation and the measures that can be taken to avoid or decrease the problem.

I am dismayed to read that Damp Proof guarantees are worthless.

How does a ‘normal’ householder know who to trust in these matters?

Tess

Tess, I’m afraid the answer is the same as it has always been. You do sufficient research to understand what questions should be asked and answered, and to let the experts know that you have a clue. Exactly the same is true for getting a car repaired or getting yourself/family repaired.

Suitable questions are:
– how will you determine whether it is X or Y?
– what do you think is the most important question that we need to answer?
– if it is X, would you do Y or Z in this case?
– what leads you to the conclusion that it is X and we should do Y? Couldn’t it be Z?
– can I see a sample contract and guarantee? (And understand why the
exclusion clauses are there before bothering to read what’s covered!)
– do you do X?
And if they say “no” when “yes” would be to their advantage, then I’m more inclined to believe them when they say “yes” to other questions.

In my experience the professionals enjoy talking to someone that already knows a little about their subject and is also prepared to listen to their advice and understand it.

I hope that hasn’t patronised you!

Is the Property Care Association a reputable source of surveyors who can come and visit my house?

Thanks
Tess

Dry Rot

We’ve had a number of posters in recent weeks advising that, despite previous injected dpc treatment, problems continue in their properties. Others have commented on conflicting advice, together with wildy varying prices. Clearly something is amiss.

There is no doubt that there are reasonable damp and rot specialists out there; I can name you a couple. I can, however, also name a vert many who in my experience will gild the lily. One of the problems is that the contractor has a vested interest in selling his product. He is not impartial on any fair reckoning. And the lay householder has no way of telling.

In previous replies, posters have been directed to publications by the likes of Historic Scotland and SPAB. It’s hard to see how you could claim that either body is an “envagelist hobbyist”, not least as the former is a government department with something more than a passing knowledge of heritage management issues. I would suggest that their opinion is to be preferred over a “specialist” who might have completed a couple of weeks’ training provided by a trade body.

If you want to discuss the technical aspects of damp, then come forward with a cogent and reasoned argument rather than an ad-hominen attack. If you want to discuss the BRE advice (much of which is glibly ignored by “specialist” damp firms), then I have a copy here. Do you want to review what the Massari publication or the University of Edinburgh paper really says, then come back with a balanced case? Shall I dig out my copy of Ashurst, or perhaps the joint EH/HS guide to the green treatment of rot? How about trying to explain to me how a dpc “cream” will work when injected into an impermeable granite or whinstone/greywhacke wall? Then we’ll find out who the “evangelical hobbyist ” really is.

Tess

If in doubt, speak to an RICS qualified (i.e. chartered) building surveyor with experience in the conservation and repair of traditional and/or historic buildings. They have nothing to sell, will invariably have been through a 3 or 4 year college/university course before completing several years of practical pre-qualification experience, and albeit that they charge a fee, it can save you money up front. Or likewise a conservation architect (RIBA/AABC/RIAS/RSUA, depending on where you are in the UK)

Mic-Fly

You have before you a report by a qualified surveyor, who has undertaken a full building survey and advises that this is not something to be unduly concerned about. He’s not selling anything for or on behalf of a rot/treatment firm and will presumably be RICS qualified. Unless there’s something obviously amiss then I’d be tempted to take his advice at face value.

Take a look at the Historic Scotland or SPAB guidance referred to in previous posts. This gives you an idea of the kind of issues you should be watching out for.

In Need of Advice:

Based on your description, it sounds like the first objective should be to provide “user-proof” ventilation. There are a number of ways to do this including permanent ventilators (“strip vents”) in windows, although these are often expensive to retrofit, air bricks into the rooms, or the installation of mains-powered extract fans with humidistat controllers in the bathroom & kitchen areas.

I wonder, however, where the damp could be coming from? Obviously the kitchen and bathroom (especially the latter) can introduce significant quantities, but bedrooms aren’t usually so much of a problem. Have a look at the Historic Scotland Inform Guide on dampness to get some pointers.

Hi All,

I’ve been reading this thread for over a year. We have significant damp/condensation problems in our house – we approached a company via this website who identified most of our issues as condensation related (which we agree with). We have made significant changes to our house, including:

1) Replacing all our windows (26!) with new ones with trickle vents – most of which left open
2) Installing extraction fans in all 3 bathrooms connected via humidistats
3) Installation a whole house ventillation system upstairs
4) Installing 2 high powered heat exchange system downstairs in the basement and 1 unit in a room with issues on ground floor – all connected to humidistat
5) Ripping out entire kitchen so we could move cooker to external wall for extraction straight through wall via powerful cooker hood.

There are no water leaks – everything has been checked, yet despite all the ventillation (nearly every unit run all day) we still have humidity in the house of 80-95% in all rooms (although since whole house ventillation we have no water running down the walls!). We live in a Valley and we think that we just live in an area with moist air and there is nothing we can do.

Not very helpful I guess but thought I’d share our situation for the benefit of the thread – ventillation helps but is not always a cure – we are still scratching our heads on what to try next.

Sorry forgot to mention the bathroom comes off the bedroom-more of an ensuite

Have you measured the outside humidity to see whether you are in a perpetually moist environment. Sounds unlikely though.

Interesting situation, ggg. Do you have any near neighbours? If the problem really is your location, then they should be suffering the same problems. If they aren’t, then what’s different?

Outside is around 10% lower than inside circa 75% RH – if there is anything else we can try/investigate please let me know. Its a detached house (original bit around 1890) with walls which are solid and around 3 foot thick – its also built into a hillside with the basement being underground (previously a cellar which someone thought they would tank and make a gamesroom – not a great idea).

All our neighbours have problems but all are different due to different types of property, we also all suffer from Valley cough from time to time! My point is that achieving the perfect 40-50% RH might not actually be possible?

For some context here’s a picture of our house from last year.

http://www.flickr.com/photos/104132026@N06/10069426284/

Quite a typical morning picture with the mist above the Valley.

Hi 999,

I carry out surveys weekly where mould and humidity have caused problem. Although PIV’s and such are great tools, it is always essential to get good information before specifying, particularly when such a lot of work and expense is involved, as in your case.

It is not always just a case of poor ventilation; air temperature is key also. To get the true picture and compare the condition outside with those in, you need temperature as well as RH. RH alone tells you very little, simply because a small decrease in air temp will drive RH up and conversely a small increse will drive the RH down – all without reducing or increasing the water vapour in the air. This point is crucial. There are cases where installing a PIV will make matters worse (though this is uncommon).

For example I visited a small flat, last week where mould is a problem and the local authority installed a PIV as a kneejerk reaction. The mould carried on being a problem and I was called in.

After the compulsory cup of tea and chat with the tenants it became clear that the electric storage heating was far too expensive for them to run, as was the electric emersion heater. Thus the flat was often kept at only 15 degrees C with the use of oil based radiators for quick delivery of localised heat, combined with a hot water bottle filled from the kettle when watching TV (yes fuel poverty drives some people to that).

More time chatting and it became clear that the kettle was also used to boil water for the sink (to wash up pots), and of course fill the hot water bottle.

Thus the high RH was due to lack of adequate heating combined with excessive moisture production vie the very frequent kettle boiling. Add a cold (if dryer), air supply through a PIV and the benefit of the new air ‘dryness’, is lost with the depressed air temp. Using data loggers over at least a couple of weeks period, prior to specifying would have helped identify these issues and maybe that would have been a good idea in your case.

I am not saying that is the cause in your case, I’d have to survey the house to do that, but it is an illustration, as your question implies – it is not just about ventilation.

The above also illustrates how important it is to talk to home owners/tenants and get as much information as possible.

Dry Rot.

I totally agree and I am very aware of the importance of correctly heating a property and not drying clothes etc – this is one reason why we are re-doing our kitchen as we want to ensure that in future all steam from cooking is ducted outside – what we found intersting is that we have not been able to cook for the last two months (apart from microwaving in the porch) so we have not generated any moisture and the kitchen has remained at a very high RH.

The problem of damp and condensation is actually very complicated with many subtle factors but also it also takes a long time to see if any particular remedy is working!

Our ventillation system is not purely PIV we have extraction as well and has been a success up to a point – the problem we have now is how to proceed to make it better.

In your situation I would do some long-term “surveys” myself to attempt to rule certain possibilities in/out. What I suggest below presumes there is no penetrating and no rising damp (no comments from heritage house, please).

Get one or more humidity+temperature sensors; typically they are called weather stations and are surprisingly cheap nowadays. Best if they measure 0-100%; some only do 20-80%. The first one I saw, from maplin, costs £30.

Get a handheld non-contact thermometer – the first one I saw was £30 from maplin.

Measure the temperature and humidity of the air in the room. Use the non-contact thermometer to measure the temperature of the surface of each wall and window etc. Keep a log of the measurements over the day and over the year.

From the standard graphs of temperature vs dew point
(e.g. http://en.wikipedia.org/wiki/Dew_point#Calculating_the_dew_point)
and the above measurements you will be able to see just how close/far from the dew point each surface is. Obviously the higher the margin the better!

If you find some surfaces are below the dew point then you have two choices: (1) raise the surface’s temperature or (2) reduce humidity by removing water from the air.

If there is a large temperature gradient across the wall it is possible for water to condense inside the wall, so if the other side of the wall is cold and the wall is porous to water vapour, that should also be considered.

Obviously if there is a lot of water vapour in the external air then frequent air changes will (without de-humidification at the point of entry) bring lots of water vapour into the house.

This advice is worth what you paid for it.

Hi – yes I think I will start to have a go at data logging. I did buy some humidity sensors from Amazon (£5 each) which I positioned around the house which has been useful to detect we have an issue but being able to capture and graph the data will be a step forward.

Hopefully people reading this will see that there is not always a simple fix – I wish we just had a water leak somewhere (perhaps we do!)

Thanks.

IMHO humidity in the middle of a room is not directly of interest w.r.t. condensation. Humidity is, of course indirectly interesting, but what is directly interesting is the dew point. Having a non-contact thermometer is a good way of assessing the dew point on various surfaces around the room.

Besided, non-contact thermometers are cheap and fun to play with, and are even useful for other things, e.g. calibrating ovens and radiators etc!

Your comments about what you’ve tried and what has/hasn’t worked are very interesting. I suspect/hope many in the industry already know all these things, but I/we don’t. Thanks.

Ah – just realized that we have one of these already for the baby (well now toddler) – I shall commandeer for my investigations!

Thanks.

ggg

1. Is there any insulation at all, and if so then what kind?

2. What’s the central heating regime?

Hi Peter,

The walls are all solid so no cavity insulation, only insulation is in loft which up to current standards.

Heating is oil fired rad system, as part of our attempts to control problem we installed new stat so house is controlled to never go below 12c – that seems to have improved things but combined with increased ventilation means we are burning almost 4000 litres a year which frankly is costing us too much – I am considering putting up insulated false walls in the really cold areas as a last resort.

Thanks

Everyone seems to be missing one vital point. Are the buildings concerned ‘solid walled, and built with breathable materials’ or cavity walled.?

If we are talking solid walled – then problems will continue until breathability is established – lime plaster, porous walls, etc – will prevent excessive build up of condensation and wick it away. Such a structure with gypsum plaster or cement render will trap water into the structure and make it even colder and better able to conduct heat – thus increasing condensation. ‘Old’ buildings, solid walled – need to be allowed to breathe.

I surveyed one today – in which the RICS surveyor had insisted needed to be tanked, and injected by a property care association member. The walls were lime plaster, limewash, over limestone and lime mortar – in superb condition. There was NO damp anywhere – a carbide test showed totally dry. Interestingly the thermo hygrometer showed 80% RH internally. This is an unusual property in being beautifully original, and lovingly restored with traditional materials. It was in perfect condition – no moisture, no condensation, nothing.

The surveyor is now being reported to the RICS professional standards committee and a negligence claim lodged by the owners.

Fortunately, more and more people are asking questions, and becoming informed.

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Well I’m not blaming anyone for our situation nor are we using any chemicals. We bought our house 4 years ago we are working with what we have – ripping the plaster from all the walls might well solve it but that’s not really an option I can consider unless I come into some money or can guarantee it will solve the problem (though I am doing that in the cellar with the intention of lime mortaring – that’s a wip) – if a higher than normal RH is nothing to worry about then that’s interesting given that everything I’ve read says that anything above 70 is too high. We do accept that we live in the country and it’s not like living in a timed frame built modern house but that doesn’t mean we should accept towels that never dry, mould forming and damp smells.

Hmm.. silly question I know – but are the walls dry? Have you drilled and checked to see there isnt moisture in them? Heat loss in solid walls is quite low, if they are dry, but increases a lot if damp. Windows – double glazed? EH and others recommend things like roman blinds – good insulators at night. What feed temp on rads? Keep it down to about 40 – rmemeber – rate of loss of heat is proportional to excess over room temp.. Hard to comment more without knowing a lot more – Ventilation on its own isnt really a good idea – as you observe – you just chuck warm air away – best to try and attack any moisture sources, and recognise that RH can go up if weather is damp – you cant win all the time, unless you have a whole house system that controls heat, RH and air quality – which isnt cheap, and frankly, generates horrible air – a lot of people dont like passivhous for that reason. Keep feeding info at us – your comments are interesting and all of us would be interested in seeing your problems solved !
Pete

Ok, but the ventillation system essentially replaces the inside air with outside air only passing it through a HRU to save energy costs – so really what is the difference of having the trickle vents open – its the same air? I can understand not having the trickle vents open in the rooms where the air is being extracted (which we don’t).

Please note that I’m posting here for the purpose of letting people know the issues we have had and the results we have seen thus far from the work we have undertaken – what this forum lacks are real case studies and updates from people who have received advice, followed it and have hopefully solved their problem – I guess if they do they move on and don’t read this forum anymore!

Dryrot,

Thanks for that – I will check out linkedin, I should really do data logging – the company I work for does telemetry including devices which measure RH and temperature – I’ve just not installed them because the rooms in question are out of reach of my wifi signal (stupid thick walls) – I will have to get that sorted. I’ve downloaded the bs5250 so will have a read in my spare time.

Cheers

Hi ggg (you can see I am old and half blind as I have addessed you as 999 in the past),

The data loggers are only about £50 each – I use LASCAR ones. The data is taken at whatever intervals you fancy – I use half hour or hour as any shorter gives too much info. Either use a psychrometric chart to convert to Vp in kPa or the Vaisala calculator and you can see what the balances are between moisture and temperature. The graphs the software supplies can help you get a better understanding as they include RH, air temp and display a dew point set too. Of course what you like to see (amongst other things), is a nice big gap between the air temp and the dew point temp (especially in poorly insulated dwellings)… playing with these will expand your understanding.

The ‘scurrilous’ damp proofing industry, which is routinely slagged off on mass here, do great courses on this, including condensation workshops and master classes – these are short but crammed with gold dust knowledge and they’re cheap too. Of course only the really good damp proofing firms, who are dedicated to improvement, attend these courses, but they are open to all.

DryRot

Good morning GGG,

I understood that the only issue was high RH? Is this just because of a hygrometer reading, or have you some symptoms which are visible; mould; damp patches and such? Persistent RH’s of 80% plus can lead to mould on surfaces and even on clothing, leather and such, so if this is not happening it is unlikely that the RH is at that level for much of the time. This is where data logging is so useful – it enables all the peaks and troughs to be seen and ironed out. It can also take account of surface temperatures via ibuttons.

If the walls look dry, then don’t bother drilling holes in them, you are only causing damage for no gain – if they were wet they’d be cold and at high RH’s you’d have condensate forming on them.

Forget about breathability – walls as thick as yours don’t ‘breathe’ in that sense, the amount of water vapour passing through the decoration, plaster, inner leaf, rubble, outer leaf over a 24 hour period is but a tiny fraction of what leaves by the door, window of extractor fan each and every second.

Breathability only matters in the outer zone of the walls – ie the face of the stones or the face of render – ie lime pointing/render = good – cement render/pointing = bad.

Keep focused; what is ruining your enjoyment of the dwelling? Address that, but avoid digging for technical problems which don’t really matter.

Finally, you say you keep the house at 12C.. that is on the cold side and will tend to increase RH so with cold solid walls the dew point may be reached. Whilst BS5250 says that the walls may have a temp 10% below the room temperature, this can mislead, as the bit of wall behind furniture, where the effects of the heating are reduced, can be orders below this. I have blogged on this with good detail but I cannot point you to my blog as this thread is toxic in some quarters and I’d be attacked by the cabal.

Good luck with it ggg

DyrRot

Hi Dryrot,

I should say that the minimum we keep the house is 12C, normally we are around 17.5-18C when actually in the house and not in bed. We have eliminated most of the mould forming behind cupboards with the whole house ventillation and by not having furniture too close to the walls, we do still suffer from mould forming round windows where it gets wet and in corners of certain rooms (the cellar is a different story that has pink mould growing on the very clammy walls – the one wall I ripped off the plaster and is now just stone feels much better). I will start my logging this weekend as I’ve been given some kit from work.

I am interested in reading your blog (and any others) – not sure how you can communicate it to me though without posting my email address.

Rose

I’m afraid that it’s impossible to give a definitive answer without seeing more information. As a general rule, however, you need to rule out any possible sources of dampness in the area focussing on leaking pipes. Bear in mind that dampness can travel a surprising distance from a leak so check both sides AND the rooms above the patch.

Den

What kind of plaster is it? Modern gypsum-based plasters (the brown coloured Thistle and Carlite types) are typically poor where there are dampes and/or salts present.

That said, the key is to try and work out where the moisture is coming from. What age and type of construction is the terrace?

Den

Rising damp, where it does exist, would be typically found at the base of the wall. I’m thus a bit intrigued as to why the PCA surveyor has diagnosed it as appearing half way up whilst the floor level is dry. Have I misunderstood?

Hi Peter, No you have not misundestood. The floor level is giving a very low reading for moisture and in some areas as low as 5% once you check about a metre up the wall the ready is 30% to 50% moisture detected.

If it is rising damp I am baffled as to why the reading is so high in the middle of the wall and also where the mold is appearing on the exposed bricks.

Will let you know what the 2nd company suggest.

Simple – its already been damp proofed once and very typically water is being forced up behind the first lot of waterproofing plaster and coming out in the middle where it can get out – this is a very common problem. Get rid of all the tanking plaster down below and get the wall breathing, and you’ll not have any more problems!

Hi Den,

Rising damp will when active give higher readings at low level than higher up. However, if it is controlled by a DPC (chemical or otherwise), there will be a residual ‘salt band’ higher up the wall, where the threshold of evaporation used to be. This will remain damp due to the hygroscopic nature of the salts. Merely plastering in cement render or dry lining will remove the surface salts, leaving the deeper salts in the brickwork forever.

This is why damp proofing companies always remove and replace the plaster at low level – to remove the salts which are concentrated there by years of damp rising and evaporating.

Of course, I or anyone else cannot diagnose damp over the internet so get good advice and do your research. There are very good independent damp specialist surveyors out there (try the PCA website) and some RICS chaps too – but if using RICS you should stress that you wants detailed advice on damp as many do not provide this service, but those that do are usually very good.

Some contractors also can be honest and very helpful – you can always tell when they are bulling you… listen and think; did they take time; look inside and out; give broad or detailed advice and do they justify their recommendations with sound methodology or just spout opinion and rush to a ‘treatment’.

Good luck with it.

DryRot

Den..
You always know when someone is talking rubbish – rising damp – has never been proven. Anyone recommending the pca has a vested interest. I refer you to previous discussions about dry rot..

We aren’t allowed to give out references on this forum, so a bit tongue tiede, but you are being fed a lot of rubbish. Do your research – try googling damp in old houses, and go from there…
Pete

Rising damp is referred to in two documents referenced several times in this conversation- from Historic Scotland and SPAB. Presumably their is some foundation for its inclusion.

Lynda

Traditional solid stonemasonry walls work differently from modern cavity construction inasmuch as they absorb moisture in wet conditions and then allow it to evaporate in more clement weather. The application of a proprietary waterproofing agent, for example one of the clear repellant systems, will actually act to trap water within the stone and accelerate decay. It is to be avoided at all cost.

When assessing the condition of such a wall, important things to check are the condition of the mortar joints. Is mortar missing, allowing water to penetrate far more quickly and deeply than would normally be expected? Have cement repairs been undertaking, potentially trapping water within the core? Are there hard surfaces like tarmac paths around the base which may be encouraging splashback wetting?

My advice would be to ensure adequate heating and ventilation to the affected areas, keeping a close eye on it for a few more months in order to see whether it might be slowly drying out. Continue to check for leaks at heating and water pipes, drains, and so on.

Having inspected the mortar joints there are 2 small pieces missing. Also the area in front of the sandstone has a mesh membrane with decorative chips lying up against the stone, could this be adding to the problem?

Lynda

My advice would be to have a look at the Historic Scotland Inform guides; there’s a good one on dampness generally, and you might also want to look at the ones on stone/pointing:

http://www.historic-scotland.gov.uk/informguide-damp.pdf‎

http://www.historic-scotland.gov.uk/informguide-limeandcement.pdf‎

http://www.historic-scotland.gov.uk/informguide-rubble.pdf

There will be English equivalents by SPAB and others, but the underlying advice is likely to be broadly similar.

Yes – save your money – take salty plaster off, allow to dry, brush salts off, and plaster in lime.. paint with breathable paints..

Hi Mils,

Chimneys with salt contamination can be a long term problem due to the aggressive hygroscopic salt content from the flue gasses. These are not common efflorescent salts, so of course you cannot just brush them off, as this only removes the salts which are not a problem and leaves the problem salts behind.

These salts are in the old plaster and have arrived there, either due to a leak at stack level/ingress of rain down the stack and/or very high RH’s in the flue, which can lead to some of the salts (ammonium sulphates and Nitrates), becoming deliquescent. This means they are then mobile in liquid form, so they migrate to the warm side of the wall – ie the plaster.

All the repairs in the world will not remove the salts, so the plaster must come off. The naked brick will be hygroscopic too so merely applying a lime plaster will not change that. Remember Mils, most of the water added to any mix – cement or lime, is not required for setting (even less so with lime), it is just there to make the product trowelable. So of course much of the ‘free’ water is absorbed into the masonry as plastering proceeds; plasterers call this ‘suction’. The clean tap water thus absorbed will dissolve salts already in the brickwork and become salty.

Now then, as the lime plaster dries evaporation at the face will draw that moisture through and hey presto – hygroscopic lime plaster and a return of damp patches, particularly in humid weather.

The solution is either use a harder material, such as cement render which is dense and less likely to allow passage of water (salts can’t walk so only move in solution). OR – ensure that the new plaster is not in contact with the brickwork at all, either via a membrane or by a lathing system to allow dry lining with plaster board.

Both methods have merit but whatever you do, do not apply plasterboard using dot and dab plaster onto naked brickwork; the gyroc adhesive loves salt! And remember that if the masonry is very soft and friable the dry lining or membrane method is preferred; so too with listed or historic property. The aim is a dry surface for decoration so focus on that.

‘Salt Damp’ is the search term to use to look into this in more detail if you want to delve deeper.

Good luck with it

DryRot.

You cannot, and should not, ever trap salts or anything else into the structure. By using cement, you are condemming your property to more problems in the long term. Even the name dry rot has connotations – try googling damp in old houses and see what you come up with – we can’t give references in this forum, so are really about as useful as a needle in a haystack – but what you have been advised is rubbish. Keep it simple – let it breathe, remove salts, and keep everything breathing – it will sort itself out.
Pete

With respect, a membrane method is not normally recommended for the care of historic stonemasonry walls whether friable or otherwise. I know of no such advice from HS/EH/SPAB or even authors such as Ashurst.

The objective should be to stop water entering the historic fabric, not to manage it through plastic membranes fixed to the internal face. Failure to do so simply means that the deterioration of the masonry continues, albeit unseen.

A lot of damp problems on chimney breasts are caused by hygroscopic salts caused by the burning of coal over many decades (sulpherous fumes result in large amounts of sulphates permeating the bricks and mortar around the chimney). In such cases you can’t really deal with the source of moisture.

I agree that membranes have the disadvantages of lack of breathability and causing damage to the underlying fabric due to the large number of fixing plugs required. However I would contend that they are probably the least bad option in the circumstances and have the advantage to the homeowner that they are pretty much guaranteed to solve the problem. It is easy to forget that not all old houses are national treasures and sometimes the occupants just want an effective and simple solution.

Robusto

Yes and no:

1. If the flue is no longer used, then vent it at the head and foot in order to minimise build-up of dampness.

2. Have it swept before sealing (or if easy access is available) in order to try and remove sooty material which may contribute to the problems.

3. Make sure that the flashings, copes, pargings, and weatherings are all tight in order to minimse the scope for water penetration.

4. Strip back the linings and ensure that the masonry is in good order. if the brick or stone is affected to the stage where it has lost its matrix then consider indenting and/or localised repointing.

5. If the level of salt contamination is so bad that it cannot be replastered, then I would strap & line over membrane applicaiton inasmuch as the former IMHO traps the dampness within the stone and can exacerbate underlying weakening issues.

Of course caution is always required when strapping & lining potential problem walls in order to ensure that you’re not merely concealing a problem and creating a potential safe haven for a nasty rot outbreak.

Realist

Putty plasters: finishing coats aside, there’s a blast from some hairy experiments we all did in the 1990s. I can’t remember the last time I saw someone using anything other than a hydraulic mix, even on listed proeprties, although I acknowledge that shrinkage and a need to tamp back become an issue.

Whether such plasters are suitable for post WWII houses is very much debatable, given the additional cost and risk involved. We perhaps have to be careful that someone doesn’t mention clay plasters, I suppose.

One thing is clear, however: never use gypsum based plasters anywhere there is a meaningful risk of salt or water ingress. In my experience they’ll be off like the proverbial greyhounds if problems do occur. Limelite may be far from perfect – they term “lime” is indeed misleading – but in a modern building it’s probably the most realistic solution once the underlying dampness has been sorted.

I, among others, have listed links to Heritage Scotland and SPAB publications that deal with damp. I think, as a non-expert, that they seem to give a good introduction to damp causes in old buildings. They allow people with a damp problem to consider possible causes and remedies and have a more informed discussion with any “expert” they might ask for advice. However, rising damp is referred to, so presumably you accept this can occur (even if generally only in the lower 300mm of a wall for example)?
The maintenance of breathability of structures and surfaces is a point well made throughout this conversation, and chemical treatments or materials that destroy this are to be deprecated. No doubt many reading these posts will take this on board.
It would be useful if Which? could extract the facts from this conversation and produce a summary of what people with damp problems should know and do, and what they should avoid. I wonder if that would excite more controversy?

Malcolm

This seems to be in danger of turning into a flame war between Heritage House and Dry Rot, something I don’t think is particularly appropriate for this kind of forum.

I agree with you that the publications of HS and SPAB are a good starting point. The former is a government department with more than a passing knowledge of historic structures, including the care of their own estate. We have provided links to their advice and I would very much encourage readers to work their way through such publications before coming to any firm views on the ways of dealing with dampness.

As for rising damp, I do not personally doubt that it exists in both theoretical terms (the Edinburgh paper on the physics of capillary movement, for example) and practical terms. What I would dispute is the presumption that it is endemic to anything like the extent proposed by damp proofing “specialists” or that an injected dpc is necessarily the correct way of dealing with it.

In my experience, many cases of “rising damp” are in fact due to misdiagnosis of penetrating dampness (especially on lime mortared stonemasonry buildings) or have been exacerbated by poor management. I used to smile when I saw someone trying to inject a chemical dpc into a whinstone wall instead of improving the ground drainage, but now I just despair.

The other thing which perplexes me is the public perception that PCA members are seen as the automatic experts in contrast to, say, independent building surveyors (note: I am not an RICS member) or other professions. And yet we hear here stories of differing diagnoses, multiple rounds of failed treatment, and so on.

It’s enough to make you cry!

Roberto

Upon reading your post, I turned and picked a slightly dog-eared copy of Massari off the shelf. The Rome 1993 edition, for what it’s worth, which according to the receipt inside cost me £24.50 from Archetype in Fitroy Square back in 1998.

There were markers at two locations:

Page 88, beginning with “capillary interception with resins” (that’s an injected dpc, for any homeowners till reading) moving on to trenches (only if the dampness is due to surface water management) and “worthless pseuodscientific methods”. I especially like the section on Electro-osmosis.

Page 177, “Cooling, not water penetration”, or in other words “check for condensation and dew point”.

I must admit that I don’t agree that all of Massari’swork is relevant to other parts (predominantly northern) of Europe and consideration has to be given to construction techniques. But yes, I read it years ago and would concurr that anyone working in the field should have made themselves familiar with it.

Robusto

There’s a reason that we used to use slate DPC in mass masonry construction, at least in areas where we used more porous sandstones (there is obviously little point in granite/whin/greywacke areas), and even if building a new mass stone wall today I would look at incorporating some sort of physical barrier.

I’m always cycnical about the relevance of these very large southern European walls with the salt “tide mark” 1.5m up the outsidfe inasmuch as they are so very different from the kind of constructions we see in most of northern Europe and certainly the UK. Indeed the four key issues in determining the scope of rising damp, where it exists, seem to me to be:

1. Thickness of wall.

2. Construction of wall, i.e. porosity of both the stone and the mortar matrix.

3. Amount of water in the surrounding ground surfaces.

4. Evaporation / Microclimatic issues.

In my personal experience, and I have to say as I was always taught at university, rising damp is rarely (if ever) seen more than 300mm above highest external ground level on a traditional mass masonry wall 450-600mm thick in this country. The highest extent tended to be where the core was an open/rubble/mortar mix – the “sponge” effect, ground water levels were high, and where surrounding surfaces could exacerbate wetting through splashback.

Under those circumstances I have always:

a. Ensured that penetrating dampness on the faces was controlled through a robust programme of hydraulic lime repointing, including core voids, the hydraulicity determined to suit local conditions.

b. Improved ground and surface water drainage at the immediate foot of the wall in order to ensure that water is not tending to pool around the footings, including cutting-back metalled pathways and pavements. I should add that, although a believer in French drains, care has to be taken to ensure an inadvertent reservoir is not created in heavy clay soils.

c. Where a new solid floor is being cast in, turning the DPM up the inner face of the wall 450mm above ground level in order to limit the scope for transference to internal linings. That said, I often use either lath & plaster on studs (for historic work) or gypliner (modern work) rather than plastering on the hard.

Problems I have seen on other projects where injected dpcs are used include the inevitable concentration of salts and dampness within the lower section of the masonry leading to accelerated weathering and spalling of natural stone or softer brick faces.

I should also say that, where I work, lime harls (i.e. hand cast renders) can help in increasing avaporation from the external faces and thus controling rising AND penetrating dampness in a subtle but important way. This does, however, tend to be restricted to historic properties.

As a final shot, I’ve always been a little worried by those who advocate limecrete slabs being laid directly onto hardcore without a DPC on the basis of breathability. This is, of course, only really an issue in the conservation & repair of “properly” historic structures however it seems to me that it only works until you put a moderately impervious tile or floor finish above, at which point the game is a bogey. I wouln’t recommend it.

In summary: it’s very complex and independent, impartial advice is usually a good thing. But said advice has to come from people who have studied and understand the issues.

Perhaps some discussion of why the Dutch don’t even bother to use dpc’s would be interesting – they live with their feet in water – but have long ago stopped using or specifying them. Makes a mockery of everything we do over here – I teach architectural students, and whenever a bunch of Dutch students appear, they fall about laughing when confronted with what they call our ‘Quaint English Custom’ of dpc’s.

Give me some links to technical and/or academic papers and I’ll happily read them, as long as they’re not in Dutch!

Presumably poor soil conditions in the Netherlands would tend to countenance against creating slip planes using dpcs, but I’d be intrigued as to how they control dampness.

It would be interesting to know which northern european countries use dpcs, and which don’t. Other than Holland, which has been cited before, do you know of others?

Failure due to movement of the substrate (i.e. bearing surfaces) or masonry structure. How serious it is depends upon a range of factors, not least whether it is ongoing or historic.

If in doubt then construct a structural engineer.

Bule

Your suggestion is correct: find the source of the pentrating dampness. Treat the cause, not the symptom. The Historic Scotland guides I linked to earlier would be a useful starting point.