Rising Damp: How to Recognise It and What to Do

An Overview

If you are experiencing problems related to damp in your home, it is important that you read the symptoms correctly. There are various causes of damp, but one of the more serious underlying problems is rising damp.

This is caused when moisture from the ground rises vertically up through fine pores in masonry or brick walls in a wick-like fashion, which in hydrology terms is called capillary action. Water can rise up the wall to a height in excess of 1.5 metres.

Once this happens, the moisture affects the plaster in internal walls which is highly absorbent. As ground water contains dissolved salts, when the water evaporates, these are left behind in the wall and on its surface.

These salts fall into three categories:

Sulphates: These appear as a floury crust on the wall which is unsightly, but do not cause any damage.

Nitrates and chlorides: These 'hygroscopic' salts absorb moisture from the atmosphere and are invisible. Unless these salts are removed, even if the underlying cause of the rising damp is dealt with, the problem will not be cured, as they will continue to draw moisture in.

The horror of rotting floorboards hiding beneath the carpet
The horror of rotting floorboards hiding beneath the carpet
Plaster that has bubbled and cracked due to damp
Plaster that has bubbled and cracked due to damp

Diagnosis - 10 Symptoms

How can you tell if you have rising damp? The following are typical symptoms:

  1. Mold on walls and furniture
  2. Rotting window frames, skirting boards or floorboards
  3. Wallpaper that lifts
  4. Paint won't adhere to the walls
  5. Stains/tidemarks on walls
  6. Flaky or bubbling plaster
  7. White powder or crystals appearing on the surface of the walls
  8. Damp or wet patches appearing on the walls
  9. Crumbling mortar between bricks or stonework on the exterior of the building
  10. Rusting steel and iron fasteners.

Staircase subsidence caused by deterioration of the supporting floorboards
Staircase subsidence caused by deterioration of the supporting floorboards

The Dangers

If the rising damp is extensive, structural damage can result. The photograph to the right shows a gap of approximately an inch between the stair and the skirting board. This is due to the sagging of the rotting floorboards that support the staircase. There is a danger that the floor will collapse completely.

In addition, health problems can arise for those living in a damp property, such as allergies and respiratory illnesses cased by the growth of dust mites and molds.

Rotted skirting board
Rotted skirting board

Identifying the Cause

First, you have to find out where the moisture is coming from and how it is getting in.

If the dampness begins at ground level or below, it may be that your damp proof course (DPC) may be faulty. If your property has suffered subsidence, it is possible that the DPC could have been damaged. Some older properties do not have a DPC at all, or if they do, a physical membrane may have failed or been bridged. To find out whether this is the case, you will need to make a more in depth investigation, but before you do so, it is best to eliminate all other possibilities first.

Consider the following:

  1. Ground levels surrounding properties can rise over the years as garden debris accumulates, and home improvements like decking and driveways are added. Check the outside of your property to make sure that all surfaces are not carrying water to a level higher than that of your DPC. All surfaces abutting the walls of the property should be slightly sloped so that rainwater drains away from the building.
  2. If you have cavity wall insulation, check that this has been properly installed. It should not go below the level of the DPC.
  3. Broken or blocked guttering, drainpipes, roofing and flashing contribute greatly to damp, causing water to leak onto walls.
  4. Check that there are enough airbricks around all sides of the building and that they are not blocked. They should be positioned every 180cm (5ft 11in).
  5. Check the brickwork/rendering, etc., of your chimney for any damage to the waterproof surface.
  6. Check that kitchens, bathrooms and boilers are well ventilated to carry condensation away. Dehumidifiers work very well in removing moisture from the atmosphere.
  7. Check that waterproof sealant and grouting is intact in between walls and shower trays/bathtubs.
  8. Check pipework for leaks, particularly at joints.
  9. If damp is appearing in walls above a fireplace, it could be that hygroscopic salts are drawing moisture in.

Courses of Action

Once the source of moisture has been identified, the first thing to do is to remove it. Leaks and external rainwater goods like guttering and drainpipes need to be fixed. Good ventilation through rooms and beneath floors must be re-established, and all drainage issues addressed.

It's only once the above issues have been addressed that a new damp proof course should be installed, if deemed necessary.  After that, any remaining rotten internal woodwork should be removed and replaced, and walls repaired and redecorated.

A Word on Internal Walls

If the damp has been caused by condensation, it is not necessary to remove plaster. It is sufficient to clean it and allow it to dry out. The next thing to do is to add a coat of fungicidal paint containing zinc oxychloride (ZOC) before adding your chosen decorative finish.

If the problem has been caused by rising damp, however, it is strongly advised that all old plasterwork, which will contain the moisture-attracting hygroscopic salts, is removed. When re-plastering, a plaster mix containing a silicone-based waterproofing, fungicidal additive should be used.

In cases where it is not practical to remove the old plasterwork, there is a product called Platon plaster base, which is a clear, high-density polyethylene membrane. The idea of this is to isolate the old plaster from the new, eliminating the need to remove the old hygroscopic masonry.

My pretty old French property has no damp proof course
My pretty old French property has no damp proof course

Beware of the Sharks

If you are unable to carry out the work yourself, you will need to call in an expert. But be careful. There are many firms that purport to be able to solve damp problems, but rising damp is often misdiagnosed. Sophisticated sales techniques exist to persuade unsuspecting people to pay for expensive damp treatments that may not be necessary. Even if the correct diagnosis is made, the products being sold may not be suitable to address the fundamental causes of the problem.

Many companies offer a free appraisal and diagnosis, but it is in the interests of commission-based salesmen to diagnose major problems, even where there are none, or to sell specific products produced by their companies which do not address individual needs. The best thing to do is find a reliable independent expert to come and advise you.

To illustrate this point, I was recently quoted almost 8,000 euros, or over $11,500, to have a system involving the insertion of ceramic tubes at intervals around the exterior of my old stone-built French property. That price was not for the whole house, by the way, just for the two worst affected rooms. It was made to sound like a perfect solution, with the salesman offering an insurance policy valid for 30 years (which I would have had to pay for), and a promise that if any damp reoccurred within that time, I would get every centime back. He also offered an easy payment package.

However, this particular company's solution would have not solved my problem, as the damp was originating from underneath the building. If the salesman had bothered to look behind the property, he would have seen that the guttering needed replacing, and that water was collecting in a gulley behind the house. His solution of dealing just with the walls at above ground level would not address the underlying cause of the damp.

Even allowing for the fact that the work was covered by an insurance policy, once he had clinched the sale and earned his commission, that would be the end of his firm's responsibility to me. When the damp resurfaced, as it most certainly would, I would be left with the hassle of claiming on the insurance policy, and I'd be out of pocket until (or if) that paid out, not forgetting the continuing monthly instalments until the issue was resolved. And on top of all  this, I'd be back to square one with the damp problem. I dread to think how many people have been caught out in this way,

So do be careful, and remember, if your wall looks all right, it probably is. If it has any of the symptoms described above, you may need to look into things a bit more thoroughly, but make sure you get good independent advice.  Good luck.

Comments 8 comments

Peter Jackson 6 years ago


Your post is very helpful and in your single post you have informed about the symptoms, causes, and the most important how to treat this problem? Rising damp is a very dangerous problem for both the houses and the property and needs to b treated with full care and properly. The best way to treat this problem is to recognize the source of the problem (leakage sources). climatic conditions play a major role, particularly in the levels of the exposure of buildings and their location near the sea or in a marine environment. In the earlier days the historic buildings are constructed without damp proof course. The water present in the ground moves up the wall carrying with it various salts. The upward movement of this water can cause saturation and can result in damage to timber, plaster etc. The wall is made made up of porous materials which easily absorb the water. Specialist damp proofing companies needs to be called which will provide the treatment for rising damp. They suggest the surface treatment for rising damp and the re-plastering on internal walls using dense mixes combined with water proofing agents.

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crystolite 5 years ago from Houston TX

Nice information,thanks for writing.

Ladisci 3 years ago


We have recently sold our house, and the survey done by the buyer shows that we have "high level" of damp on our chimney breast, lounge and kitchen and the report said that the cause could have been a failed damp course. Now the problem that I have is that we do not have any sign of dampness at all. For us was a shock, as we didn't have any idea! We have no patches, no flaky plaster or wall paper, no tide marks or similar. also we have have a gas fire, so the chimney breast is not capped and therefore I believe some water my come in, but I believe is normal. However now the buyer is having another report from a specialist, should I be worried, am I missing some other signs, a part from the ones reported by the damp reader? Thank you in advance! Laura

Jay 2 years ago

Hi your post is very useful i found it very hard to diagnose the cause of the mystery damp patches but with a lot of internet searching i found a product called the wet wall warning and it proved it was only condensation

lesley 24 months ago

Can anyone help please I think I may have damp on an internal wall which is also a supporting wall that is dead in the middle of our terraced house it is only on that wall I didn't think internal walls could get it..Lesley

Mark 21 months ago

In response to Ladisci, although the post is old I may be able to provide some helpful info to others. Basically the surveyor was an idiot. Any high readings around the chimney area on his "moisture meter" would most likely have been Hygroscopic salts in the plaster, not a failed damp course. The damp meters they use should be banned as they are almost totally useless for the job unless you are highly skilled in their use. They measure electrical conductivity and salts will give a false high reading. If it is an old house and the fireplace burnt fossil fuel then these contain salts that eventually leach through the brickwork into the plaster. If it is not damaging the decorations then no action is needed at present. Otherwise the area can be replastered with an aluminium membrane underneath.

audrey thomas 15 months ago

my house is rented had black damp in bedroom for 6 years damp sealed it still comes back

mod 5 months ago

its so educative thanks

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