Damp Problems

Damp is a problem which affects almost every kind of property and there is not always a simple solution. Damp patches can be unsightly, at best, and, if the source of the problem is left unchecked, damaging to the structure of your home.

There are many excellent sources of information about the various forms and causes of damp in buildings (listed below for reference) but here I’ll look at how damp causes problems specifically with internal decorations and offer some advice on how to deal with it.

Types of Damp in Buildings

Penetrating damp

Water can get into the fabric of a building in any number of ways – from defects in brickwork, blocked guttering, broken roof tiles, leaky plumbing and so on. In many cases these forms of damp can be difficult to diagnose as the leak may not take a direct path to the problem area internally. However, once the fault is found and remedial action is taken there should be no further problems – provided you allow plenty of time for the affected areas to thoroughly dry-out.

Once the problem is fixed and any residual damp has dried out you may need to block stained areas with an oil or solvent based sealer to prevent any subsequent discoloration but that should be about it.

Single Thickness Walls

A common problem, however, particularly with older properties, is that the exterior wall is a single thickness which allows moisture from the outside to soak its way through to the inside. In itself this shouldn’t be a major problem but the use of modern gypsum plaster finishes, washable paints and vinyl wall-coverings means that this moisture becomes trapped and causes problems over time.

The solution involves ensuring that internal plaster-work and decorations are breathable – which will necessitate removal of existing plaster and re-covering with a lime based plaster followed by the use of water based paints with little or no resin content – or traditional paper based wall-coverings without a washable surface.

Another option, and one which tends to be favoured by jobbing builders is to render the exterior surface of the offending wall with a hard cement coating. This can often cause more problems than it solves as, firstly, it prevents any trapped moisture from escaping and, secondly, as the cement ages and cracks this can let in water from the outside which can not escape again.

Rendering does not necessarily have to ruled out – it just needs to be carried out competently. The render cement needs to be softer than than the surface it is applied to and any paint coatings used must be moisture vapour permeable (able to let trapped water vapour evaporate, in other words).

Exterior walls painted with Keim mineral paint
A new build residence finished with Keim Concretal silicate based wall finish to provide a high performance and environmentally friendly solution.

One the best known paint brands for exterior use is Dulux Weathershield and this should perform well when used correctly. Consider also mineral based paints such as those supplied by Keim. These are specifically formulated for the purpose and form a mechanical bond to the surface which results in a very durable finish whilst allowing the building to breathe as intended.

Covering Over the Problem

Of course, in many cases, a householder may not want to go down this route for reasons of cost and inconvenience in which case there are alternative ways around this which, ultimately, involve covering over the problem with a view to dealing with it properly at a later date.

Beware of what seem to be magic solution – water proof or damp proof paints will only mask the problem for a short time and will eventually fail. A tried and tested solution involves the use of pitch and foil backed lining paper (applied with a strong water-resistant adhesive) which provides a sound surface for re-decoration. It should be emphasized  however, that this method should only be considered where the amount of damp ingress is moderate or where previous water damage has mostly dried out.

Damp-proof foil
A foil and pitch backed lining paper will provide some protection from slightly damp walls – but this can only ever be successful as a temporary solution.
Available from amazon.co.uk

Rising damp

Rising damp is the effect of moisture movement from ground level through the fabric of the building in the absence of an adequate damp proof course. There is a lot of misinformation about regarding the subject of rising damp, mostly because the ‘damp proofing’ industry has an interest in exaggerating the problem and offering expensive solutions – sometimes serving to make the problem worse in the long-run by trapping moisture within the fabric of the building. Or, in some cases, simply diverting the damp problem to another part of the building.

This is not to say that there are not operators who provide a professional and effective service – just that you need to be on your guard when taking advice from a so-called ‘surveyor’ who is often no more than a glorified salesman.

There are three approaches you can take when trying to tackle rising damp:

1. Prevention – taking measures to prevent damp rising in the first place, ranging from the insertion of a physical damp proof course to chemical injection or more advanced measures such as electro-osmotic damp prevention.
2. Reduction – from lowering the ground levels to exterior walls and installing better drainage to replacing internal finishes with breathable alternatives.
3. Concealment – covering the problem with the use of water proof sheet materials or dry-lining.

As always, prevention will be the preferred solution but the alternatives can be effective, if done properly.

Reducing the ingress of damp to a manageable level is achievable – for instance, as with the problem with single thickness walls, replacing hard Gypsum based cements and plasters with a traditional lime based alternative will go some way to achieving an effective long-term solution – provided you only use permeable decorative finishes.

Breathable Matt Emulsion Paint
A trade matt emulsion with no vinyl content will allow any moisture in the wall to slowly evaporate

A contract matt emulsion such as Dulux Fast Matt will perform well on surfaces subject to slight damp because there is little or no vinyl content – allowing any slight water vapor to pass through the surface. Environmentally friendly lime, clay or casein based paints (or Eco paints) are very effective in these situations but can be more costly and offer less choice of colour.

Concealment of the problem can never be a good idea in serious cases but, again, where the problem is minor, it can provide  satisfactory results. The traditional method of concealment would involve fixing a corrugated pitch-fibre sheet material to the wall and covering with plaster – with the inclusion of air gaps at the top and bottom to promote ventilation.

Installing Platon Membrane to a Basement
An installation of Platon membrane to damp basement walls

A modern alternative of this is to install plastic Platon membrane to the wall and finishing with a waterproof plaster or plasterboard dry-lining. Anyone contemplating this kind of solution would be advised to seek out a contractor specializing in this kind of work rather than leaving it to chance. Triton Systems offer a range of waterproofing solutions and maintain a list of approved installers who can offer a fully backed guarantee for all work completed.


Condensation forms when moisture in the air comes into contact with a cool surface. This is most noticeable in areas of high humidity such as bathrooms and kitchens and is relatively simple to deal with.

Ways to reduce condensation include:

  • Reducing the amount of moisture produced inside the building
  • Increase heating levels and improving thermal insulation
  • Improving ventilation generally around the house.

Improving ventilation in the affected areas will solve a lot of cases – leaving a simple clean-up with a mild solution of diluted bleach or a fungicidal wash to clear any surface mould before priming with a stain blocker and redecorating.

In problem areas, where the amount of damp is quite minor, you may want to resort to using an anti-condensation paint which works by holding some of the moisture – allowing it to evaporate slowly over a period of time rather than just running off the walls and ceilings and collecting in one area – as with conventional paint systems.

Of the products on the market Rust-Oleum 5090 Anti-condensation wall paint seems to be about the best available (albeit quite pricey!). Products you’ll find on the shelves of your local DIY store are generally not very good and quite expensive for what they are.

It is worth noting that old fashioned emulsion paints (the non-washable types) served just this purpose before vinyl based alternatives became commonplace – so you could, if you wanted, use a contract matt emulsion for ceilings in the kitchen and bathroom rather than fork out for expensive specialist paints which more or less do the same thing?

For more serious cases improving the thermal insulation to the cold side of the affected area may help. This may not be a simple job – depending on the area concerned and you may need to take professional advice on the best way forward. Products such as thermal linings (thin polystyrene that you stick to the wall before decorating) rarely provide a satisfactory result and are best avoided.

There are a range of products available now which dramatically improve the insulation values of internal walls but these need to be professionally installed and can be quite expensive. It’s worth noting, however, that this kind of improvement can be carried out under the new Green Deal scheme – so may not involve any initial outlay on your part?

Interstitial Condensation

Condensation forming within the layers of the building fabric is known as Interstitial Condensation and this can be the most problematic and difficult form of damp to eradicate – but it shouldn’t be ignored as it can contribute to a serious deterioration of the building’s structure.

As our homes have become better insulated then interstitial condensation has become more widespread – incorrectly fitted loft insulation is one major culprit. The omission of a suitable vapour-check membrane (a sheet of polythene above the plasterboard) is a common problem because the work is often unseen and unsupervised – and so difficult to put right after the fact.

Further Information



Sherry – What is the best way to deal with recurring black mould on internal concrete(?) walls in the stairwell of our block of flats? It is a very damp building in general. The managing agents are getting it repainted without any thought or preparation (because it’s not their money they’re wasting!). READ MORE…

The mould is likely caused by condensation, warm air coming into contact with a cold wall. It’s unlikely the stairwell is heated and poorly ventilated, which is why it will keep recurring unless the underlying problems are addressed.

At the very least, I would expect the affected areas to be treated with a fungicidal wash and re-painted on regular basis with mould-inhibiting emulsion such as Dulux Trade Sterishield.

It may help your case if you take photos before any work is done, immediately afterwards and again in 6 months time. If the mould is just as bad within this timescale then you would be right to argue that the agents are indeed wasting money. I would also ask the agents for the specification of works carried out as further evidence.

John – A few months ago I painted (a first coat) on the exterior of a small farm house, in the north west of Scotland. I used Sandtex Fine textured PBW. It has solid stone walls which have been rendered. The weather stopped play for 6 months, but on going back the other day, I noticed that along the roof line it did not look as if it had been painted at all, it had weathered off completely. I was sure the surface was dry at the time as we’d had very good weather, and it certainly wasn’t flaky; I know it may be difficult to give a concise opinion, but would you say this would be more down to the surface NOT being adequately dried or more to do with it not having had a second or third coat before the Scottish weather prevailed..? READ MORE…

Could well be damp within the walls which, in such an environment, can be very difficult to mitigate. Sometimes rendering a solid stone wall can cause more problems than it solves since any damp below the surface will never escape.

Since you say it is the roofline that was affected I would also check that there are no defects that are allowing moisture to penetrate and build up below the surface in that area.

New rendered surfaces can also present a problem with alkaline based minerals working their way to surface as apart of the natural drying-out process. I always recommend allowing new render at least 12 months to ‘weather’ before painting.

Often these things never have one single cause and it is a combination of factors to blame. It can be a frustrating experience but ensuring you are starting with a totally dry surface to start with is the first step.

Chris – Some years ago a plumbing problem led to my loft flooding, and the water found it’s way down the walls of the bedroom underneath. My decorator treated the bedroom walls with a stain blocker, papered over with woodchip paper, and then painted over. From the outset there were small patches where the paper bubbled away from the walls, and now there are larger areas where the paper is coming away. Is this to be expected? Or is it more likely to be down to poor decorating, or to other problems I haven’t anticipated? READ MORE…

The walls haven’t dried out properly. Is this poor decorating, well, he should have known better but it’s the kind of thing that can happen to any of us.

The problem is not so much whether he should have waited longer (obvious with hindsight) but what is he going to do about it?

Richard – I live in an old stone built solid wall construction house and in one area of a doorway the paint keeps blistering and flaking. It does not appear to be damp, there don’t seem to be any colour changes in the plasterwork and the MDF skirting is showing no signs of blowing or deterioration and there is no damp smell. It affects an area from floor level to approx 3′ 6″ off the floor. Any thoughts or suggestions please. READ MORE…

Defective mastic seal around the door frame or loose pointing are what springs to mind but, obviously, I can only guess?

‘At floor level’ also suggests a lack of or defective DPM resulting in a minor case of rising damp?

John – I have an older rendered gable wall. The render appears in reasonable condition but the wall is very weather exposed. We have just had a new kitchen on the inside of the rendered gable, the builder advised to paint the wall, as when drilling into the wall it was very wet. A great part of our problem is a very high humidity. In your opinion will painting with a good waterproof paint help and would using a stabiliser help or hinder given the wall is so wet? READ MORE…

I have lost count of the times I have had to answer similar questions. Your builder is a an idiot and what you suggest is the worst possible solution.

Why is the wall so damp and what can you do to allow it to dry out. If you address these two questions you have solved the problem. Trapping the moisture within the wall is only ever going to end badly.

Natalie – We have an unheated below ground vault attached to our kitchen, which has been tanked and plastered, 7 years ago, but never painted i.e. raw normal pink plaster currently. It has a dry powder all over it – what product do we need to use to prior to painting with breathable clay based paints? Or is it best to just dust it off and do mist coat of clay paint, followed by two coats – we don’t want to seal moisture into the walls as they are below ground and need to breathe, so am unsure about using a stabilising coat….? READ MORE…

Remove the the dry powder, which is probably efflorescence, with a dry brush and then paint with a breathable emulsion. Clay paint is ideal or, alternatively, something like Dulux Fast Matt that has no vinyl added.

Thin the first coat so it sinks into the surface; you may need to experiment depending on the quality of paint used but 40 – 50% is a good rule of thumb. Then finish with two normal thickness coats, or slightly thinned to ease application.

You may notice dark patches here and there later on but this is just trapped moisture escaping and perfectly normal.

Denis – I have an 1892 semi built into a hillside. The back wall of the basement is below ground level. This wall appears to have been tanked at some time, but damp patches have developed, most probably due to leaks on local water board pipes in the ground behind.
After over six years these leaks have been rectified, so the water board says. I want to sell the house and I am reluctant to go for a full membrane installation with drainage channel since this would be disruptive and the choice would be better left to the new owner. Also, I think it would be overkill since there has been no actual water ingress.
So I want to get the place looking respectable and get it on the market. At present the paper has been stripped off the bottom of the wall. The top half was never affected by damp patches. I have thought of repairing the cracks in the tanking (with what?), treating the affected areas with salt neutraliser (where do I get it?) and replacing the paper with horizontal lining paper to match the existing. READ MORE…

The proper course of action would be to investigate the source of the damp and to take remedial action. Your mention of cracks in the tanking and use of salt neutralisers (available from any builders merchant, btw) suggest this isn’t a minor issue?

However, if we assume you’ll be making full disclosure to any potential buyer, you could ‘tidy things up’ by using a standard lining paper with an extra-strong pva based adhesive, then painting with fungicidal emulsion paint. This will probably last a couple of months before any evidence of damp starts to show though.

For the sake of cosmetics I don’t think it’s worth going any further, since any temporary fix will fail eventually? I suggest you make all efforts to dry out any damp before starting though; it may be worth using a dehumidifier also (sometimes cheaper to buy than to hire, btw).

Suggested products:

Mangers Heavy Duty Adhesive
1200 Grade Lining Paper
Johnstone’s Stop Mould

Judith – I have mid terrace house, attic walls each side adjoining chimneys keep showing damp on plaster travelling down from roof, had roofer seal, point and cowls put on wood burning stove chimney and extractor in kitchen chimneys, the other side has been capped as neighbours don’t have fires, one roofer said strip plaster off and repoint, but l have tenants in with small child that uses that room with asthma and the disruption would be too much. I have painted it with oil based damp seal and it works for so long then cycle starts again. READ MORE…

If the chimneys have been capped there needs to sufficient ventilation at high and low levels to prevent a build-up of condensation. It’s very common for this not be done or, where it has, done poorly. As you have witnessed, you can only seal the surface for so long, the water will find a way out eventually.

I think the only practical way you are going to solve this is for the child to sleep somewhere else until the work has been done properly?

Bill – Moved into our Cottage October 2015. The original building which incorporates the Lounge is 150 years old and the Damp Course needed replacing which we had professionally done in April 2016 approx with plaster being hacked off and replaced etc. The exterior walls have been rendered and pebble-dashed some years ago.
After a couple of months we redecorated using a water based Dulux Matt emulsion. Honey gold shade. After a few days to a week, stains started appearing on the rear wall which is adjacent to a full length door to garden and above a window. I rubbed the area down and redecorated once again but the problem re-appeared and just this one wall has quite few stains which is unsightly. We were advised by y the Damp company a month or so later,, that they could not have known about the moisture within the wall and to fix the problem would need replastering using a different process which would cost around £600. They also said that if we leave it for 18 months or so it may dry our itself ? It’s now about 13 months on and I would appreciate your advice and comments as we don’t really want to waste more money. We do have double glazed windows throughout and there is a condensation problem which we are aware of and deal with best we can. READ MORE…

It is ironic that the damp company say they couldn’t have known about the moisture in the wall?

This aside, chemical damp treatments (which is what I assume we are dealing with?) can only alleviate an existing damp problem – not cure it completely. The walls will still absorb moisture from the ground, externally from minor cracks in the masonry and from the atmosphere (albeit at a lesser rate) and this moisture needs to be able to escape. Rendering the external face of the wall and painting the internal face with a standard emulsion paint are only going to impede this process.

Now the plaster has had sufficient time to dry out in depth you should be OK to decorate BUT you should only use a non-vinyl base emuslion such as Crown Covermatt or Dulux Supermatt.

You can only buy these paints in white or magnolia although, if you buy from a trade stockist, they will be able to mix a colour to your choice. You will need to thin the first coat with water by at least 10% as a primer btw.

There are also clay based paints available that are also breathable, although they can be expensive. You do get a nicer colour choice though.

The bad news is that these kinds of paints are not very effective at holding back stains so, if you do have any problem with discolouration, choosing a shade that doesn’t show this up so much can sometimes be the only option.

As always, before committing yourself to further expense, it may be wise to paint a test area first? Maybe on the worst affected area and leave it for 2 weeks to see what happens?

Ross – Our external, underground water meter was found to have been leaking for many months leading to water soaking up into ground floor bathroom and kitchen walls in an 1890s mid-terrace. The leak was stopped over a year ago and drying has gone nicely with added air bricks into double skinned wall. The exterior wall was painted white prior to the leak and stained through. Removing all the paint from the wall isn’t realistic to reveal bare brick to breathe so is there a breathable paint option you could recommend? Or is it just a case of stain block now the damp has gone? The air bricks could remain but of course the double skinned wall provides insulation – the floor is concrete, not suspended. READ MORE…

If the staining is fairly minor an application of stain block is probably your best bet. However, if it’s more severe I would suggest using a coat of Pliolite based masonry paint to cover the stained area only followed by one or two coats of regular water based masonry paint.

Since Pliolite paints are solvent based it is less likely the staining will migrate through to subsequent coats. It’s not a certain solution but one that’s worked for me in the past. Just leave as long as possible between coats, at least 2 days.

Zinsser also have an exterior primer they claim is breathable but I have never used it so can’t recommend one way or the other.

If this doesn’t work, a choice of colour that doesn’t show the staining so much is an option worth thinking about.

Emily – We are currently putting a new kitchen in our end terrace property. We have lived in this property for a couple of years and always knew there is an issue with damp. We have had to take all the plaster off the wall in the kitchen as a damp detector said the walls were off the scale damp. The kitchen has a suspended floor, we have pulled up the floor boards to have a look and there is a lot of wet sand under there. What would your advise be for the walls and under the floor? READ MORE…

It is hard to say without more details but I would advise you contact a qualified surveyor before you go any further. And I mean a proper surveyor who is a member of RICS, not someone who works for a damp proofing company who is just a glorified salesman.

The cost of a professional survey may be disheartening but will probably save you money in the long run.

Dan – I’ve recently purchased a house built in 1890, there seems to have been a historical condensation problem within the house which I am remedying with a good extraction system.
Some of the walls on the ground floor are a little damp, although these have started to dry out since removing the wallpaper. It looks like a previous owner had invested in an injection based damp proof course and the lower half of the walls were replastered in gypsum plaster. In an ideal world I would remove the gypsum and replace with Lime, but sadly I am not able to do this at this time. I have been looking at a Ronseal product called Damp Seal which claims it is breathable, do you think it is a good idea to apply this to the wall prior to repainting with a non-vinyl emulsion, do you have any recommendations of paint ranges that aren’t really expensive that might be suitable? READ MORE…

I wouldn’t use any products of this kind because they will inhibit the drying out process. There are circumstances where they are useful (usually when people put their house on the market and want to hide such problems) but, since this isn’t the case here, I would just allow the walls to dry as much as possible and then apply a couple of coats of contract matt emulsion. Dulux Supermatt and Crown Covermatt are ideal for such situations.

You may get some staining where the damp is at its worse but try and live with it if at all possible (mid-tone colours tend to be better than very light or very dark colours). In time, when you are confident the worst of the damp patches have dried out, using a stain blocker for the worst affected areas may be worth considering?

If the walls have been treated with a damp proof system and covered with hard gypsum plaster then it is unlikely the internal damp problem will persist. The way the work has been done however, as you seem to already know, is not ideal but only time will tell how effective it has been.

Kerry – Semi detached Old house with stone walls. Been modernised internally with gypsum plaster (drywall) everywhere and re rendered outside walls. Internally the plasterboard is discolouring (lots of yellow/brown spots) almost covering the walls and book lice. Chimney breasts have salt contamination and rising damp in hallway (confirmed by a damp proofer) but moisture levels on walls are supposedly ok? So what’s causing the discolouration? READ MORE…

The discoloration is caused by damp. Walls absorb moisture and it needs to escape somehow, you’ve just blocked it from both sides. Funny how some so called ‘experts’ are able to be ignorant of this basic fact?

Paul – Problem with damp interior solid stone wall of end terrace house. Render to exterior in good condition. I removed the interior ground floor render to allow wall moisture out. I coated with interior earthborn breathable paint. Two weeks later the interior of the wall is turning green with mould- any suggestions please? READ MORE…

Can only speculate since you have supplied few details but this indicates the walls are damp. The external render is likely impeding the drying-out process also.

Chris – Does Stormdry work? It is supposed to stop porous brickwork etc water resistant. READ MORE…

It does work as a water repellent and is also breathable. In ideal conditions it’s worth using as a primary defence but for existing damp problems it is not the right solution.

Andy – I have a farmhouse that dates back around 250 year. In the kitchen there is an exterior wall that also contains a chimney. It seems to be retaining a lot of water and on humid occasions the moisture build up causes leaching of the plaster dye through the paint.
It has also resulted in the paint lifting from the surface. I am sure that this problem has been there for many years and there have been many attempts to fix it. Could you advise on the best short and long term options. READ MORE…

The obvious problem that springs to mind is a buildup of condensation due to lack of ventilation. It’s fairly common for unused chimneys to be capped at the top to prevent ingress of rainwater but the chimney space needs to be adequately ventilated, and this is something that often isn’t done or, when it is, it’s done poorly.

Ideally you’ll need a means for air to enter the chimney space and to be able to escape. This is commonly achieved by inserting airbricks or ventilation panels at the top and bottom of the chimney stack. If this has already been done it may be a case of just needing to adding more in order to improve the airflow.

Viviene – Rear upstairs interior walls of new build house have been painted with watered down paint but house is not fully water tight. Front downstairs room and upstairs front room have no windows in and roof at this point is also not finished. Plaster looks dry but I think painting at this time when house is not water tight and has no heating will cause a problem. I’m being told it’s fine to do this but I’m unhappy about it. READ MORE..

You may be right to be unhappy but your typical housebuilder and his contractors will most likely carry on regardless. All you can do is gather evidence in the form of photographs and a written account of what’s going on and who said what. Should you have problems later on you can use this to pursue a claim in the small claims court.

Having said this it’s possible you won’t see any long term problems, the paint may flake off here and there but the damage is likely to be more cosmetic than anything else. This, of course, is no consolation and I fully sympathise with your predicament.

Phil – I have a damp issue in a upstairs bedroom outside wall. The damp appears next to a divan bed- I believe the gap between the mattress and wall is causing the issue. However the room is so small that the bed cannot be moved into the room. Would you recommend foil wallpaper for this case? READ MORE…

It would just move the problem elsewhere really. Not the answer you’re looking for but the only way to prevent this problem is to give the room a good airing at every opportunity. Can the bed be moved during the day, maybe on it’s side, to let air circulate around the room?

Jessica – I have recently had some damp work completed on my very old stone property.
I’ve been advised to buy microporous paint…instead of vinyl. Could you offer any advice as to how I can tell if a paint is microporous? Or what paint brands offer this? We have currently been using the Valspar range from B&Q READ MORE…

Most decorative wall paints have vinyl resins added to make them more durable and washable. But if there is moisture in the wall it can not escape and will cause these kinds of paints to bubble and come away from the surface.

So, what you want is a wall finish that doesn’t have vinly added. Some trade emulsions, such as Dulux Trade Supermatt, are formulated for use on newly plastered walls and are breathable or ‘microporous’.

There are also clay based paints which have the same breathable properties but have more ‘eco credentials’ and provide a richer, more natural finish. They are pricey though.

The only disadvantage with either of these paints is the are not easy to keep clean as any marks can’t be wiped off, you need to ensure you have some spare paint for touching up – ideally from the same batch.