/ Home & Energy

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

Damp companies that offer ‘free surveys’ may seem appealing, but our latest undercover investigation found several companies recommending unnecessary treatment that could cost hundreds of pounds.

Everyone loves a freebie, but if you’re tempted by the ‘free surveys’ on offer from damp-proofing companies, you may end up spending more than you need.

In our snapshot damp investigation, we invited damp-proofing companies to carry out an assessment of our properties’ damp problems. In two thirds of cases they recommended unnecessary or inappropriate treatment, or missed the problem completely. But does that mean you have to pay to get good advice?

All we needed was a plumber

In one case, our property had a leaky toilet – and any damp specialist should have instructed us to get this fixed before the room could even be assessed for other potential damp problems.

There was no evidence here of rising damp, and yet four of the eleven companies told us that we needed to install a chemical damp-proofing course in the walls and re-plaster the room – at a cost of up to £1,440!

That’s not to say all the companies were bad. We did see some good practice, with just over half of the companies that visited this property giving us helpful advice.

How to get good damp advice

Deciding whether to take your chances with a free survey, or shell out hard cash for independent advice is a toughie. Even though I’ve seen these results first-hand I know I’d be tempted to try my luck with the free option first – although I’d make sure to get at least three companies to come round and quote for the work.

Then, if there were inconsistencies in the work recommended or I had any inkling that the work might be unnecessary, I’d definitely consider getting an independent damp specialist round.

If you think you might need to call on a damp company, check our damp advice guide first for info on the different types of damp that can affect your home (if it’s just suffering from condensation you won’t need a specialist).

[This Conversation has been closed and is not open for commenting.]


My property, a 1930 semi, has some penetrating damp. The cavity wall ties almost certainly need replacing. The previous owner installed urea foam cavity wall insulation (a very brittle white foam) over 25 years ago; it may or may not have voids in it.

Will replacing the cavity wall ties damage the foam insulation, thus increasing the penetrating damp?

Is there a way of removing the cavity wall insulation to restore the cavity?

Is there a way of replacing the cavity wall insulation?

The cavity wall insulation is not itself a defence against penetrating damp. Penetrating damp is usually caused by a building defect such as faulty rainwater guttering so the correct approach is to deal with the building defect directly. Defective wall ties can cause dampness to bridge the cavity so it is important they are in good order. The National Insulation Association should be able to provide advice on removing and/or replacing cavity wall insulation.

Since I can’t reply to David Prince’s reply, I’ll have to reply to my own comment.

I understand the need to remedy the building defect. Presuming that is done correctly, I will still need the cavity wall ties replaced.

According to a research engineer at the Building Research Establishment, it is normal for driven rain to result in water running down the inside of the outer leaf – that’s why the cavity is there in the first place. Will replacement of the cavity wall ties result in such water being transmitted to the inner leaf?


I thought the main purpose of a cavity was to provide insulation. Mortar spilt on wall ties and poorly installed cavity wall insulation are common causes of penetrating dampness.

Wavechange wrote:
|I thought the main purpose of a cavity was to provide insulation

No. Google for “cavity wall” and read any of the top references.

I stand corrected, tomg. My knowledge, for what it’s worth, came from a time before Google had been invented. 🙂

Best of luck with getting your problem fixed.

Hi Tom, defective cavity wall ties definitely should be replaced to maintain the structural integrity of the building. There are specialist contractors who will carry out this work. The replacement wall ties are designed in such a way as to prevent dampness/water bridging the cavity.

Gas hobs and ovens are unflued appliances and can create a lot of condensation in a house. Using an externally vented cooker hood helps but will not eliminate the moisture put into the atmosphere as a result of burning gas. Using pan lids helps a lot. Simmering and boiling furiously cook food at the same rate, but many people don’t appreciate this.

Gas fires with a chimney help remove moisture from the air. Making more use of a gas fire and less use of central heating can help decrease condensation, and keep gas bills down.

SallyP says:
13 December 2011

I recently renovated a single storey property that included plastering the walls and re-painting. How likely could it be that damp has penetrated a wardrobe and made clothes show signs of mildew in 4 months? There was no sign of any damp prior to the renovation. One of the companies in Which? survey visited the property and said that it was rising damp?? Could it be condensation?

Hi Sally,

Mould growth is almost certainly an indication of a condensation problem. Mould is not a typical symptom of rising damp. Plaster drying out and restricted ventilation inside the wardrobe is most likely the trigger for the problem.

Paul.H says:
15 December 2011

I have an end terraced house which suffers from what I think is Penetrating Damp over the whole of the gable end wall. There also seems to be Rising Damp at low levels around the other outer walls.Has anyone any experience of the Dutch methods, eg; Holland Damp Proofing UK Ltd. I mention these methods as the advantage is that all the work is done outside, so no plastering needs to be done. The workmen don’t even need to come into the house!

If we take the case of rising damp then there are typically two problems. The first problem is the rising damp itself. This can be controlled by the installation of a new damp proof course. For external walls this can be carried out from the outside of the property – whatever the chosen method. The second problem is the salt contaminated plaster that usually results from rising damp and will prevent the wall drying out properly. The re-plastering work associated with damp proofing work is to deal with salt contaminated plaster rather than to facilitate the damp proof course insertion. It follows therefore that if there is a genuine rising damp problem you will almost certainly need to re-plaster. The British Standard indicates plaster should be replaced to a minimum height of 1 metre. I think there is a lot of information online about the ‘Dutch’ method of damp control which is worthy of further research. Further information may also be available from the Property Care Association (the damp proofing trade body).

David says:
16 December 2011

My 1920s house suffers badly from condensation in the 7 rooms with solid walls. Three damp proofing companies visited and each proposed different expensive treatments but none identified condensation as the problem in all of the rooms.
I’ve tried using a polystyrene wall covering. This certainly increases the surface temperature of the wall and retards the black staining but is too fragile and is not a permanent solution. Are there any treatments available to apply to the wall that can then be covered with wallpaper?

Hi David,

We use a product called ‘Ultrotherm’. It is 12mm thick and is plaster skimmed once installed. Installation of ‘Ultrotherm’ is fairly easy for anyone with DIY skills. A plasterer can be brought in for the finishing touch if necessary. The product provides a 37%+ improvement in the ‘U’ value of a solid 9″ brick wall. You should also look at improving ventilation. We install heat recovery units to limit the heat loss and of course save energy.

Andrew Farrell says:
16 December 2011

Hi David,

I live in a mid-terraced house built in 1895. There is what appears to be rising damp on the corner of the wall between the living room and dining room and the wall of the house next door. This places it exactly half way between the front and back of our house and on the wall we share with our neighbour. I wouldn’t be surprised to find damp on an external wall, but is it normal to have it at the furthest point from the outside? Does this mean it is coming up from groundwater? If so, is an injected damp course the best solution?



Hi David,

It certainly sounds unusual for a rising damp problem to appear in this way. It would be a good idea to look for other possible causes such as a plumbing leak next door.

Rising damp can affect any wall that is in contact with the ground so it does remain a possibility.

If you would like to send me a photograph of the problem to my website then I will be happy to advise you further. I’m not sure I can give the address here but you can Google it.

Dear David, earlier this year we had a damp downstairs bathroom assessed by a damp surveyor and then had work carried out by the co. that he suggested. They lined the walls and floor in a material like stiff bubble wrap – is this a good method?

Hi Raf,

I think the product you are referring to is a cavity drain membrane. These membranes are primarily used in basement work (below ground) where the dampness in the ground cannot be directly addressed. I know of a number of companies that use this approach as an alternative to damp proofing but I have to say I am not keen on the approach for dealing with above ground damp. In my view it is better to stop the damp problem where possible rather than putting a waterproof barrier in front of it. One of the common problems associated with waterproof membranes is that dampness will try and work around it so dampness can then affect adjacent areas. When we do install membranes above ground it is usually to deal with contaminated walls such as in barn conversions or where there are excessive salts in the walls.

I was pleased to see this topic raised in Which? as my son is considering buying an old house with solid walls.

In preparation I had read the book written by Jeff Howells “The Rising Damp Myth”. The case Howells argues is very similar to that put in the Which? article except, based on his experience as a bricklayer and lecturer and carrying out simple ( non-rigorous) tests, he goes further to question whether “rising damp” ie water rising vertically through a column of bricks can occur. He questions whether capillary action could cause water to rise more than perhaps a couple of bricks.

He also calls into question the effectiveness of the electronic meters used to diagnose damp in walls, the technique used to install and effectiveness of chemical damp courses and the ceramic plug system – going further he questions the independence of many of the “damp expert” companies. In fact it is very much in line with Which? findings – causes of dampness are usually simple things with low cost remedies.

I would be very interested to learn what the mechanism for “rising damp” ( ie water rising from the ground through a vertical column of bricks) is and whether it has been demonstrated in the laboratory and work published in a “peer reviewed” journal.

I think Which? may have done excellent work in raising this topic. Any comments ?

I am familiar with the book you refer to but can’t say I have read all of it so wouldn’t want to directly comment on any findings. As a damp proofing contractor I am sure you won’t be surprised that I believe rising damp does exist and that I see it on a regular basis! I think the issue raised in the Which investigation was more about the poor advice given out in remedying very real damp problems. The investigation was of course only a snapshot of the industry and should be taken as such.

I think damp proofing companies generally receive a bad press over this issue of ‘does rising damp really exist?’ Damp proofing companies get called out to properties that have damp problems and provide a solution. The installation of a damp proof course is a requirement of the national Building Regulations – try building a house or extension without including a damp proof course and see what the Building Control Officer has to say about it!

Electronic moisture meters are a useful tool but not a substitute for good surveying. Having a hammer and chisel doesn’t make someone a carpenter and having a moisture meter does not make someone a surveyor!

I would agree that many damp problems are due to simple building defects rather than failure of the damp proof course. I think it is the duty of the damp proofing company or other chosen surveyor to accurately determine the cause of the problem and give advice accordingly. This is what Which were looking for in their investigation.

There is lots of information available at or through the Property Care Association regarding the process of rising damp and a fairly recent article carried out on the subject. My view is that more dampness will rise through mortar beds than bricks.

I am a small builder on the Isle of Wight, where the earliest house I know of with cavity walls was built in 1865.

I find that a frequent cause of dampness is a build-up of powdered lime mortar and other debris which bridges the cavity above the damp-course.

This is easily remedied by taking out a brick in every 3 or 4, preferably not in the course immediately below the damp-course to avoid disturbing it, and raking the cavity clear to a depth of at least 6″ / 150mm below the damp-course. This is a straightforward operation, but quite hard on the knuckles.

Helena says:
17 December 2011

we had an extension built with a bathroom which showed signs of a salt line within 4 months above the toilet which backs onto the outside wall.The builder said this was due to the plaster used as the bricks were lo salt bricks. There is a salt line just above the skirting on an inside wall now + on a wall in a bedroom on the otherside of the bathroom,The builder swears the damp proof course was put in properly . What can we do?

Hi Helena,

I think you would need someone to take a look at this problem. A salt test can be carried out to find out if the salts present have come from the ground (an indication of rising damp). A further test possible is a calcium carbide test. This involves taking a sample from the wall structure and measuring the moisture content of the sample. I don’t think a simple moisture meter test would be sufficient in this case.

helena says:
22 December 2011

Many thanks for that David-who would you suggest to do these tests- ie what type of company-I am in the East Midlands
Many thanks

Hi Helen,

The tests can be carried out by damp proofing companies or independent surveyors, for example. Not all companies have calcium carbide meters so you would need to check with them. We have an office in the East Midlands so if you would like us to provide a quotation then please feel free to contact me through the Abbott Damp Proofing website. Alternatively, the PCA website has a list of members in the East Midlands.

peatfreebog says:
18 December 2011

We are involved with a Victorian house inLondon with solid walls. The sub-basement flat has some damp coming through, as much on internal walls as external. We were going to contact Frank Schriver UK Ltd. You mention the Dutch Company. Do you have any comments on Schriver?
Thank you

I had the schriver system fitted costing over £2000.00 for damp and mould problems as last resort, It did not fix the problem. I was told by the Shriver surveyer that it would fix the problem.
I now realise that the problem lies with internal condensation caused by the large amounts of water generated durring the living process and having nowhere to go but into the coldest walls.
The water generated used to run down the windows but now due to sealed unit windows its soaked up by the north facing walls (the coldest) more ventalation and a dehumiditier have made a big difference. When drying clothes inside running a dehumidifyer dries the clothes in half the time and produces huge amounts of water which obviously would have been deposited on the coldest walls.

I used to suffer from condensation on single-glazed windows and fitting double-glazed units eliminated the problem. I soon noticed that a spare bedroom with two external walls felt damp though there was no mould. I now keep a small window locked slightly open throughout the year, have a radiator set on low and keep the door closed to prevent moisture generated elsewhere in the house out of this room. I also keep the bathroom window locked slightly open throughout the year.

As John says, moisture generated during the living process (breathing, cooking, bathing, etc) will head towards cold walls. If you are fittling double glazing, look for windows that have some kind of ventilation.

I can’t really comment on a specific system too much. The Schriver system is a different approach to that offered by most damp proofing companies. There is information online generally and possibly from the Property Care Association. My advice is to be satisfied the system takes into account the second of the problems associated with rising damp (salt contaminated plaster) I referred to in an earlier post.


I have moved into an 1860s property that was treated for rising damp (chemical damp proof course injected) a year ago. I’m concerned that some of the walls that were treated are still damp. I can get the damp proof course reinjected if it has failed, but I’m wondering if there are things I should look into first, e.g. whether it was replastered too soon. Also, I have lathe and plaster walls and someone made an offhand comment that the damp may have got into the studs. Have you got any thoughts on what is most sensible to investigate first?

Hi Em,

It can take a long time for walls to dry out fully following the installation of a new damp proof course – even over a year. That is not to say you shouldn’t be concerned so I would advise you to contact the damp proofing contractor for further advice as the work should be under guarantee.

The length of time lapse between injection and re-plastering will vary depending on a number of factors including the type of chemical injected. As a general point of interest we find that most damp proof course beakdowns are caused by a failure of the re-plastering system rather than failure of the injection.

Timbers in contact with dampness are always a concern. The only way to check the timbers is to open the wall up to some degree.

Nathan says:
19 December 2011

Hi David,
We’ve just bought a 1809’s mid-terraced house and are currently renovating it before we move in. The damp problem we’d like to remedy is in the front bay window area, where there clearly is an issue – the original wallpaper was coming away from the wall under the window and the plaster shows staining up to around 40-50cm from the floor on the front wall next to the bay. However it only affects one half of the bay, and investigation outside shows that some of the brickwork in that area is quite eroded, by the looks of it due to rain splash or a previously leaky guttering.
We had a company over to have a look, and said it was probably penetration from outside, but they couldn’t rule out rising damp either, and suggested that we had a DPC put in for the whole front wall and/or a waterproof layer on the inside underneath new plaster.
My question is, does this sound like the right way to tackle the issue? I’m concerned that putting a waterproof layer inside might just be covering up the problem, which might then just erupt elsewhere. Is there a better way to prevent such rainwater penetration externally, other than replacing the brickwork?
With regards to the DPC, we could always get this put in at a later date from outside if the issue wasn’t solved some other way, but then again we’re tempted to just go the whole hog now as we don’t want to put in an expensive finish to the room only to have it ruined by further issues.
Thanks in advance for any advice you may have!

Hi Nathan,

The correct approach is to deal with the source of the dampness directly so you should definitely carry out any necessary repairs to the rainwater guttering etc. The eroded brickwork will need to be replaced, repaired or possibly rendered over (without bridging any damp proof course).

Building Regulations indicate there should be a minimum difference of 150mm between internal floor construction (effectively DPC level) and external ground level to prevent rainwater splash so you should consider lowering the ground level if necessary to achieve this if possible.

It is difficult to identify rising damp on a wall affected by other dampness. This is why the British Standard indicates that other damp problems should be rectified before declaring rising damp. This was an issue raised in the Which investaigation. I agree there is the issue of getting all the mess out the way in one go and this is something you will need to decide upon.

The term ‘waterproof plaster’ is used quite loosely. It can refer to the type of plaster used in damp proofing work and although this plaster is waterproof it is not vapour proof and allows the wall to breathe and dry out. The term is also used for ‘tanking’ work such as used in basements. In this case the wall surface is sealed to hold back dampness. The first version would be suitable for the bay wall but I would share your concerns about the second version.

As a further consideration, if the floor around the bay is timber then you should also check the condition of the joists and wall plates as water penetration can lead to expensive wet rot and dry rot problems.

Nurul Haque says:
19 December 2011

I have just purchased a repossed 1900 end terrace with a solid wall. The house has been empty for approximately 7 months with no heating whatsoever.

I have had 3 different surveyors who have all told me 3 different things with one solution in common – “DPC” and replastering with sand and cement. The only problem i have with it is that the plaster is peeling off in one, small about a 1/2 metre long section of the outside wall about 60cm from the floor. Where the damp/plaster is peeling off, there is a airbirck on the outside wall and i think it is penetrating damp as the air brick is almost ground level and it is a solid wall. One surveyor considered the air brick may be the problem and therefore unnecessary and should be blocked off. I cannot find any recearch on this point and you thoughts would be appreciated.

There is another patch of “damp” on an internal wall, on and above the skirking board. It is a solid floor and i have removed the skirting boards and can see that there may be a damp proof membrane underneath the concrete. A surveyor has advised that too is unnecessary and the moisture is being “led” into the wall by the membrane as it has no where else to go. He suggested work over £4000 including “floor to wall joints”, DPC, sand and cement etc…

Does anyone of the above ring true? save for the 2×1/2m damp issue, the rest of the house is fine. Any advice/comments would be grately received.

Hi Nurul,

It is frustrating when you receive different advice from damp proofing companies. The common solution (damp proof course and re-plaster) is only designed to control rising damp so they presumably agree on there being a rising damp problem at least.

Rising damp typically causes visual evidence of dampness such as tide marks and salt deposits across the leading edge of the dampness. If you are not seeing these symptoms then you should perhaps seek further (possibly independent) advice.

Penetrating dampness from an old air brick is very likely so it should be sealed if it is not required. You would need to determine why the air brick was installed to decide whether or not it is still needed. Air bricks are installed for a number of reasons including to provide ventilation for a heating appliance, to ventilate timber sub-floors and for ventilation more generally.

It would be unusual for rising damp to affect just two unconnected small areas of your property. This suggests further investigation is required. Sealing wall-floor joints is not a particularly big job so it would seem the quotation of £4000.00 is for substantially more than this part of the remedial work.

norman berry says:
20 December 2011

I live in a 1970’s detached house with “regular” bricks in what seems like a well built modern property. My problem is that one of the gable ends gets a wet streak about six feet long and 2.5 feet wide starting from just under the gutter in a downward path fairly close to the edge of the gable end. This only happens occasionally during fairly heavy rain. I have had several builders check out the area and replace a few tiles and some felt but have gone away baffled when the problem remained – the guttering/down pipes are ok !
The wet patch quickly dries once the rain finishes.
Any ideas please ? N Berry

Hi Norman,

If you would like to e-mail me some photographs of the problem I might be able to advise you further. You can contact me through the Abbott or dampexpert websites.


cfawd says:
20 December 2011

I’m having terrible problems with condensation. the windows are always dripping in the morning, they are double glazed but old. I renting the property and I’m not able to do anythign sturctural to improve things. Is my best course of action to buy a dehumidifier? I’ve tried to leave windows open slightly but I don’t live in a safe area so i can’t do this overnight. I don’t dry clothes inside and always use an extractor for the bathroom and kitchen. I’ve found mould on some of my books which I can only put down to this house as there was never any sign of it in my previous houses. Is using central heating making the situation better or worse?

very confused!

Condensation is primarily caused by inadequate ventilation. If the landlord is prepared to install ventilation units then this should solve the problem. I would suggest heat recovery units or positive pressure as a cheaper alternative. You can check out the advantages/disadvantages of these systems online.

If the landlord is reluctant to install ventilation units then the continued use of de-humidifiers would seem a reasonable option.

The issue of central heating is really that you try and maintain a steady temperature rather than highs and lows. Raising the temperature increases the air’s ability to hold moisture while lowering the temperature does the reverse. So, raising the temperature encourages the air to absorb more moisture but then rapid cooling means that moisture is deposited on cold surfaces.

I have touched on condensation problems in previous posting so it might also be worth checking them out for additional information.

Damp proofing companies are justifiably among the least trusted of operators within the service industry. This recent Which? survey simply confirms this. It also destroys the myth that if a company is a member of the PCA/BWPDA they can be relied upon to provide sound professional advice. Consumers should be very cautious about companies offering ‘free surveys’. These firms are not operating for philanthropic reasons; they need to find work to keep trading. That is not to say that companies that charge for their surveys are going to be knights in shining armour either. The safest way for consumers to proceed is to employ a totally independent chartered building surveyor to assess the problem and provide approximate costings. Armed with this, it would be very difficult for an unscrupulous operator to rip them off. This also applies to supposed woodworm infestations, where in at least 50% of cases the treatments carried out are completely unnecessary. Fungal timber decay is also a money spinner for many within the industry where wet rot in timber is diagnosed as dry rot, and people are relieved of thousands of pounds to eradicate it.

A Abbotts says:
22 December 2011

I am struggling to find an independent chartered building surveyor in the Glasgow area. Would you be so kind as to provide some ideas as to where I might find a list of companies that employ this type of professional?

The damp proofing industry has its share of problems like most industries and there is of course always room for improvement. The Which article was a snapshot of the industry only so this should be taken into account. Companies do have off days – whatever service industry they are in.

Only around half the companies contacted by Which were in fact members of the PCA so in reality this represents a tiny proportion of PCA members. In my view the PCA are an excellent organisation and will be working with the companies involved to deal with the issues raised by Which.

With regard to free surveys, I agree that consumer’s should be cautious. It isn’t and shouldn’t be the case that a free survey will always include a quotation for work. As the Which article stated a number of companies gave good advice for free and provided a report.

Using chartered or independent surveyors is already an option for consumers and Which point this out in the article but perhaps some find the fees too high. It should also be remembered that chartered and independent surveyors can also make mistakes and carry professional indemnity insurance for their ‘off days’. My advice is to use companies that have good recommendations such as on WhichLocal whether they are contractors or surveyors. The PCA also has members who are independent surveyors and offer the services you describe.

I’m not sure where the 50% figure you quoted for unnecessary timber treatment comes from but I would be interested in taking a look at it if you can provide any more information.

I don’t personally know any chartered building surveyors in the Glasgow area. Perhaps other Which members can help? You could consider using an independent remedial surveyor. The PCA should be able to help with this.