How to Cure Cold Spots and Damp on Internal Walls (2024)

Cold and damp spots on internal walls can be a nightmare, causing both condensation and black mould growth to form. Despite the visually unappealing nature of this, it can also cause quite a bit of damage to you home and also in the case of black mould, to your health.

In this project we look at all the issues that can cause cold and damp spots and then how to fix them and the damage they cause, read on to find out more.

How do you Know if You Have Damp, Cold Walls?

The first point to cover if you think that you have cold or damp spots on your walls is top actually confirm this by testing the suspect area, this can be done in one of two ways:

• Damp Meter: Generally, the go-to option for testing for damp, simply poke the two prongs on the top of the unit into the suspect area and the meter will tell you the levels of damp present. Damp meters can be bought form most DIY stores for as little as just over £20
• Your Hand: If you don’t have a damp meter, the next best tool to use is the back of your hand. Simple place it on the suspect area and you will be able to feel whether it’s damp or not. It’s not 100% reliable but if the issues bad enough then you’ll be able to feel it

Once you have established that an area of your wall is damp, either to the touch or by using a damp meter, it’s then time to establish the cause.

What are the Effects of Cold and Damp Spots?

Cold spots are caused by the act of warm air within a room touching a cold interior wall. In most cases this creates condensation and damp spots which in turn can create other issues of their own, so it’s important to treat your cold spots as soon as you notice them.

Generally the most common effects of cold and damp spots on interior walls are condensation, black mould, damaged plaster and efflorescence:

• Condensation: Clusters or patches of condensation form on cold spots as moisture in the air condenses
• Mould: After prolonged exposure to condensation, black mould will start to grow
• Plaster Damage: If plaster is exposed to moisture for long periods, it will eventually turn to mush and blow off the wall
• Efflorescence: Occasionally a build-up of a white salt-like substance in the form of white staining or crunchy salts will form, creating damp patches and damaging plaster

In the case of a Hygroscopic Salt issue (hygroscopic meaning water attracting), these can sometimes be more pronounced around a chimney breast.

Burning fuels such as coal and timber produces mineral and tar by-products and deposits on the inside of the chimney, among them hygroscopic salts, and over time these seep through walls and on to the internal surface of the walls.

As the salts are hygroscopic they will physically suck the moisture out of the air creating damp spots on your walls.

A characteristic of hygroscopic damp is that damp patches will come and go over time, so if yours do this then theres a good chance your damp spot issues are salt-related.

Causes of Cold and Damp Spots on Internal and External Walls

In the majority of cases there are only a few reasons why cold spots and damp spots appear on walls, so it’s now time to take a look at these causes

Rusted or Dirty Wall Ties

As you may know, wall ties are inserted between courses of brick and effectively tie the inner and outer cavity walls together, which allows them to support each other.

At the time of construction, mortar used to build the walls can fall and land on the wall ties within the cavity, if the builder is a little careless.

Over time this mortar can collect other rubbish, dust particles and moisture and then provide this moisture a direct route on to the internal cavity wall creating what’s known as a Cold Bridge.

This creates a difference in temperature around the affected area compared with the rest of the wall (a cold spot on the wall) which then goes on to cause condensation and turn it into a damp spot.

Wall ties can also rust due to prolonged exposure to moisture and water. When this happens, the rusting causes the tie to expand which then cracks the mortar it’s sitting in, often creating gaps in the external mortar.

This then allows cold air and moisture to penetrate the external wall and access the inner cavity wall, making existing cold and damp spots worse and also creating new ones.

Poor Cavity Insulation Job

For anyone that has looked at getting their cavity walls insulated you will probably know from just a brief search online that this can be a bit hit and miss in terms of success.

There are quite a few companies out there that (being diplomatic) may not poses the correct skill set or knowledge of what insulation to use (as there are several different types) and in what situations they should be used, size of holes that should be drilled and in what locations etc. or tools to do it properly.

If you are looking to get this done, make sure that you do your research first and get a professional reputable company that actually knows what they are doing.

The effects of a poor job can be extensive. If the cavity is not filled to the correct height and gaps are left in the fill then this can cause temperature variations and cold spots on your walls, which as we have stated above can cause condensation, mould growth, hygroscopic salts, damp spots and other issues.

However, done properly, cavity wall insulation can give huge benefits, mostly in the form of a warmer home and lower energy bills.

You can find out more about cavity wall insulation on our Cavity Wall Insulation page.

Penetrating Dampness

As the name suggests, this issue occurs when damp and moisture penetrate through a surface and then effect those surfaces behind it.

In most situations this is the result of failure in the pointing between the bricks or blocks of the outside wall, spalling (cracked and crumbling brick faces) or cracking in any facing render, in other words, a compromise in the integrity of the protective outside wall.

Once this has happened water and moisture can then easily find its way into the cavity and then onwards on to any interior surfaces, often dragging salts with it that then go on to cause their own issues.

The water and moisture then cause damp spots which are by their nature cold because damp walls lose heat three times faster than dry walls

Again, this attracts moisture which condenses on the damp spot to make the situation worse.

When it comes to ‘Salts’, they often get drawn out from a damp wall as the moisture evaporates from the surface. Once evaporated the salts are left on the surface as raised, crunchy deposits on and in your plaster that can also then cause it to split.

Pipes, Wires and Fixings

Another cause of damp spots and cold spots on internal surfaces can be the presence of pipes, wires or fixings within the wall itself.

On occasion during the construction of the property the builder/heating engineer may choose to run some pipe work (normally central heating related) within the cavity.

Likewise, an electrician may choose to run some wiring (possibly lighting related) from a light switch, up the cavity and over the ceiling to a lighting fixture.

This is not necessarily the best way to do things by any means and is a sign the tradesman in question may not be too reputable, but it does happen.

Similarly there can be a massive amount of fixings, bolts and screws that penetrate the inner cavity wall of your home and protrude into the cavity void. Items such as wall cabinets, kitchen cupboards etc. can use fairly lengthy fixings due to the weight they have to support.

When this happens, any moisture or water that is present in the void, whether from leaks in your roof or cracks in your mortar can have a direct path to the surface of the inside wall by settling on and running along the fixing, causing damp spots and cold spots on your interior wall.

This issue can be a good indication that you are suffering from a leak somewhere, so at this point it would be a very good idea to carry out a thorough investigation and locate the source and get it fixed.

Any gaps around your fixings will also allow water and cold air in from the cavity void, which will contribute to any damp or cold spot issues you are having.

How to Fix Cold and Damp Spots on Internal Walls

Now that we have had a good look at the main causes of damp and cold spots on internal walls, it’s time to take a look at how to fix them correctly so they don’t cause and further issues now or in the future.

Fixing Rusted or Dirty Wall Ties

As I’m sure you can imagine, as the ties are buried in the walls that form your home, fixing them if they are damaged or dirty is no easy task, however the first job is to actually establish that a wall tie is causing the issue.

The only way to properly inspect and remedy a fix is to locate the suspect wall tie. The best method for this is to hire a metal detector so that you can accurately pin point it, probably around the area where the damp patches are.

Step 1 – Inspect for Damage

Once you have located it, inspect the area around it for damage to mortar, plaster etc. and also test for damp and whether the area is colder than the surrounding surface.

Step 2 – Remove Bricks and Inspect

If you find that there is a wall tie here and there’s damp and damage, the next job is to remove one or two bricks from the outside wall and check it. Find information on how to do this can be found in our Replacing a Damaged Brick Project.

NOTE: do not remove more than two bricks at a time – if you need to so that you can clearly and easily spot any issues, please consult with a reliable builder or surveyor.

Step 3 – Clean Wall Tie

If the tie is dirty then clean it off thoroughly, removing any debris or mortar that may be present. Try to catch it and not let it fall into the cavity.

Step 4 – Replace if Rusty

If you find that the wall tie is rusty and has started to crack the supporting mortar then it will need replacing with a new one to prevent further cold and damp issues and restore the support to the wall.

For instruction on how to do this see our Replacing Wall Ties project .

Step 5 – Check for Leaks

If you have found rusting wall ties this could be a sign that water is getting in at another location, so you will also need to thoroughly check and locate the source of any leaks and get them repaired.

If left unattended this could cause huge issues later down the line. You can find more information on detecting a leak in our Tracing a Leak project.

How to Fix Poor Cavity Insulation

This issue is really only caused by poorly inserted pumped cavity insulation.

As with the wall ties issue above, the only real way to check that this is causing cold and damp spots is to remove a couple of bricks from the outside wall directly opposite your cold spot or damp spot on the interior wall.

If you are unlucky enough to find that gaps and air spaces are present in your pumped insulation then there is not really a lot that can be done other than getting installers in to do a re-injection (this may require the removal of the original insulation).

Your best bet is to consult with a reputable cavity insulation company and see what they suggest, again be sure to to do your research to find a reliable company.

How to Fix Penetrating Damp Issues

If you find that you have damaged mortar between your brick or block work then it will need replacing. See our Pointing and Repointing Mortar project for more information.

Damaged Bricks and Render

Any damaged or spalling bricks (where the faces are crumbling off) will also need replacing. This is a fairly straightforward job and more information can be found in our Replacing a Damaged Brick project on the link above.

When it comes to damaged render this will also need to be fixed. The reasons for render failing vary, but the most common reasons are that there may not be enough of a “key” for it to grip on to on the surface beneath (the scratch coat – this is a different consistency to the top coat).

Also the wall’s surface may not have been prepared correctly, it may have been laid in poor weather conditions (too hot or too cold) or cracks and splits could be the result of movement of the property over the years or settlement.

In some cases render cracks can be repaired using suitable filler and the join sealed afterwards, but this repair will always be visible, even if you paint it. If you are not too concerned about this, then this could be an option.

If you have numerous cracks running all over the face of your render then the best option is to hack it all off and re-render ensuring that the surface wall is correctly prepared.

To ensure this is the case clean all mortar joints, the face of the wall (power wash if possible), remove any paint and then paint the wall with SBR bonding slurry.

Rendering can be a tricky job so to ensure a good finish either practice first until you are suitably proficient or seek the services of a decent and reliable plasterer/renderer.

You may be thinking that a complete re-render is expensive, and you would be right! A very, very rough ball-part figure would be somewhere around the region of £3000 – £5000 but to ensure you are rid of any cold spot and damp spot issues and have a great finish sometimes you just have to bite the bullet.

The Fix for Wires, Pipes and Cables

If it’s not obvious which fixing is causing the problem, it’s a good idea to remove a brick from the outside wall directly opposite the problem area on the inside wall to see if you can locate the fixing causing the damp problem, if indeed a fixing is to blame.

The first course of action is to remove the protruding object from the wall and correctly fill the hole using a suitable solid filler (if removal is possible).

If it is not possible to remove the object e.g., it’s a heating pipe, then you will have to fill the gap around it fully. In this instance use flexible filler as the pipe work will likely expand and contract depending on its temperature.

How to Fix White Salts (Efflorescence) and Blowing Plaster

One of the major issues caused by cold and damp spots is the fact that they can draw naturally occurring salts and minerals out of plaster, mortar and a variety of masonry surfaces.

Problems Caused by Efflorescence and Chimney Salts in Plaster

Salt issues are typically caused by a water or moisture leak. The leak itself can draw the salts present in bricks, blocks etc. through the inner cavity wall where they then create a visual impact on internal surfaces.

There are 2 different types of salts that cause issues:

Hygroscopic Chimney Salts

Often, these issues are more apparent around chimney breasts (chimney salts) where the action of burning fossil fuels releases minerals, among many of them hygroscopic salts, that can condense on the inside of a chimney breast.

Typically they will leave a yellowy brown residue due to the tars that are released from materials such as wood during the burning process.

These salts are hygroscopic in nature (moisture attracting) and not only manifest themselves as a white salty substance staining the surface of your chimney breast but also attract moisture from the ambient air within a room, creating damp and cold spots and making even entire interior walls cold.

These damp patches usually come and go with the changing humidity of your room, so if this is happening, it’s likely that hygroscopic salts are the cause of your damp issues.

General Salts

There is another type of salt deposit known as ‘salts’ that appears as a crunchy, raised white deposit.

These salts are again normally the result of a severe damp or a bad leak that needs to be fixed before the salts can be delt with.

On the wall when a damp issue is present, the salts are drawn through on to the inner surface and when the moisture evaporates from the surface, it leaves these salts behind.

As with other salting issues, if left they will eventually cause huge damage to plaster surfaces which normally result in it being blown off the wall.

How to Fix Efflorescence Salts in Plaster

If you have now identified the cause of your efflorescence of salting issues it’s time to see how they can now be fixed.

Un-Damaged Plaster

The first job is to take a look at the state of the plaster in the affected area.

If it’s sound and still solid, then you are okay to treat your wall with a good quality salt neutraliser. There are quite a few available on the market at present, your local DIY store should have a fair selection to choose from.

This will stop the salts appearing and once it is dry, you can then redecorate.

Damaged Plaster

If your salts are hygroscopic and the plaster is blown, the only solution you have is to strip the plaster off and treat the underlying wall with salt neutraliser as if you don’t it will simply seep back through once more.

In terms of what products to use, you can get salt neutraliser that you paint directly onto the wall, one that’s already included in the plaster you are using to replaster, or a separate additive that you can add to your plaster mix.

Whichever solution you use, ensure that the walls surface is correctly prepared first and tha new plaster is laid on and allowed enough time to fully dry.

Multiple Damp Causes

If you have salt/hygroscopic salts that aren’t the only cause of your damp and cold walls, the first task to complete is to locate and repair any leaks and moisture points.

Take a look further down this page for fixes for different moisture sources. Once this is done, you will then have to dry the area out, removing any damp spots on the walls and taking as much time as needed, in some cases several months. Heaters, ventilation, fans and dehumidifiers can help with this.

Once completely dry, assess the damage. There is a chance that if your damp spots are fairly minor then any plaster present or surface decoration will have survived once dry.

If this is the case then you can leave the old plaster on and just treat for salts before redecorating. You can do this by applying a salt neutraliser to the surface of the wall.

Once the neutraliser coat on the wall is dry, you can then redecorate. If the damp has caused any staining on your walls, you can use a Stain and Damp primer on the area first to prevent the stains from showing through the newly decorated surface.

Again, as with all things there are a great number of suitable products available on the market today.

In most cases any consistent water or moisture ingress and damp spots to a plastered surface will damage it beyond easy repair and cause it to blow off of the wall so it will all need to be hacked off, removing the damaged area and also any affected areas around it.

With all the plaster removed, allow any further damp areas beneath to dry thoroughly and where hygroscopic salts are present, treat with a salt neutraliser.

You can get a pre-mixed salt neutraliser and plaster mix or you can get salt neutraliser that you can add to the plaster mix (as mentioned above).

Extreme Salt Issues

In extreme salt conditions it may also be necessary to apply not only the salt neutraliser but also an air gap membrane to prevent further salts from penetrating the plastered surface.

These air gap or mesh membranes are effectively insulated and pitted plastic sheets that form an insulating barrier between your wall and the finished surface.

There is a varied selection on the market such as those made by Twistfix and Dry Wall and Floor plus quite a few others, all are pretty much of a comparable quality.

Final Finishing

Now that you have dealt with your cold spot and damp spot causes, dried the area and removed any affected materials and prepped with a suitable product to prevent any further issues, if you haven’t already you can now replaster.

As with all things DIY you can do it yourself (practice first) or get a plasterer in.

At this point it may also be worth considering replastering with a lime based plaster due to its ability to breath.

With the area plastered, cover it with a suitable damp and stain primer and then you can redecorate – job done!

Fixing the Effects of Low-Level Rising Damp Spots on Internal and External Walls

Another common location for cold and damp spots is at low level on your walls, just above the skirting boards.

Problems Caused by Low Level Damp Spots

As mentioned in the title, the tell-tale signs of this issue tends to be cold spots and damp spots on your interior walls just above the skirting boards.

These areas are normally damp to the touch or there is black mould growth and a build-up of lichens and moss on the external walls.

Rising damp is, as the name suggests, damp that rises up from the water and moisture found in the ground.

To prevent this from happening, a damp proof course (a waterproof layer) is fitted between courses of bricks about 6 inches up from ground level.

The damp proof course itself can be constructed from a variety of different materials including slate (traditional), felt, specific DPC plastic membrane sheeting or retrospectively as an injected liquid.

The presence of rising damp is a good indicator that either you don’t have a damp proof course (DPC) installed, your damp proof course is broken in some way, or its been bridged.

Bridging occurs when debris in the cavity void reaches above the level of the DPC and provides a direct route for damp and moisture to by-pass it and carry on rising up into the wall above it.

Another possible cause is the external ground level or something attached to your external walls reaches above the DPC, again allowing moisture a route around the DPC, this time on the outside of the wall.

These issues will need checking on the external wall, directly opposite the affected area on the internal wall using one of the following methods:

• Confirm that you actually have a DPC, as especially in older properties, some houses have been built with no DPC
• If the DPC is not visible on the external wall dig down a few inches if possible, to look for your DPC there. If you find it below ground level then you have an external bridging issue
• If there are any structures attached to the external wall near the affected area, check these to see if they reach above the DPC. If they do, then there may be an external bridging issue
• If the DPC is visible above ground level, remove a brick or two (no more than two) and inspect the cavity for debris. More information on how to remove a brick is available in the project mentioned above.
• Inspect the DPC for damage, wear and tear and compromise

How to Fix Low Level Damp Spots

The findings of your investigations outlined above will dictate what fix you implement.

Externally Bridged Damp Proof Course

In the case that your Damp Proof Course is bridged externally, you will have to remove the obstructing object to expose the damp proof course once more.

If this is not possible e.g. the obstructing object is a fairly recently constructed conservatory, then you will need to insert a new DPC above the level of the structure.

You can do this by drilling holes into your internal and external walls and injecting a special chemical DPC liquid or cream – this is a chemical formulation that is absorbed into the brick.

Once in the brick, the chemicals join together with one another across the brick to form a waterproof layer.

You can use one of the many DIY chemical DPC injection kits available on the market such as Permaguard, Twistfix etc. Find out how to apply a cream DPC in our project here.

This fix will also be the same if you don’t have a damp proof course or if you have a DPC but it’s damaged.

Internally Bridged Damp Proof Course

If when you have removed bricks you find that your DPC has been bridged inside the cavity void by debris, you will need to clear all the debris out and ensure that no further rubbish enters the space.

To do this, remove 1 or 2 (no more than 2) bricks from the external wall right opposite the area on the inside wall. For help on this see our removing and repairing a brick project here.

Use tough gloves to do this as some of the debris may be sharp. Once totally clear, replace any bricks that you have removed and allow the mortar to dry fully before moving on to anymore.

Repair Damage

Once you have solved the source of water or moisture ingress you can then go about repairing the damage done by the damp spots.

Dry out the area thoroughly taking as much time as needed for this and then assess the results.

In light damage cases the plaster may be able to be saved. You can then treat the surface with a salt neutraliser if there are any salt deposits present, and you can remove any mould present with a good quality anti-mould cleaner.

You can apply a damp and stain primer to prevent any staining caused by the damp showing through on the newly decorated surfaces. Once the treated wall is dry you can then redecorate as required.

If the damage to the plaster is too extensive then the entire damaged area will need to be hacked off and replaced.

Any damp underneath will need to be dried out fully and then the wall’s surface treated as needed with a salt neutraliser if salts are present.

You can get salt neutralisers you paint directly onto the wall’s surface or you can get neutralisers that you add or are already added to the plaster mix you’re using for replastering.

If there are heavy salts present you will also need to cover the wall with a mesh membrane before you replaster.

The membrane stops the salts from travelling into your plaster in the future. More information on attaching a mesh membrane to your wall can be found in our Mesh Membrane project page.

Fixing Damp Spots and Cold Spots on or Around the Chimney

If you have cold and damp spots isolated to the area around your chimney breast then these will need to be delt with before any repairs can be pt in to action.

Issue Caused on and Around Chimney Breasts

The normal causes of any cold damp spots on and around chimneys are hygroscopic chimney salts. These salts, as mentioned above, mostly come from the materials that are burnt e.g. wood etc.

The mineral deposits that build up on the inside of a chimney breast can seep through the wall and appear on the external chimney breast surface and create damage in the form of white and brown staining and salt build-up.

These salts attract moisture and cause damp spots to appear on the chimney breast, which usually come and go as the humidity in your room changes.

The fact that the salt deposits are penetrating the wall could also indicate a leak, so you will also have to check any open chimney pots to ensure moisture is not getting in here and also cracked mortar, broken tiles, damaged flashing etc.

More information on what to check to find what’s causing damp in your chimney area can be found in our Chimney Damp Project page.

Another cause of cold and damp patches in your chimney area can be poor ventilation. A chimney breast should be vented top and bottom to produce a decent air flow and prevent cold air becoming trapped in the void.

If cold air is trapped in the void then your chimney breast will most likely be at a different temperature to the rest of the room, which in most situations will cause a cold spot or a cold wall where moisture in the air will then condense and cause a damp patch.

This issue can be more prevalent if you have capped chimney pots or blocked fire openings that have not had suitable ventilation installed.

How to Fix Damp and Cold Spots Around Chimney Breasts

In the event that you have hygroscopic salts creating damp spots and staining on your walls or chimney breast, and your plaster is sound, then you can fix the salt issue by painting on a salt neutraliser as mentioned earlier.

If there is any mould present you will need to clean this off with an anti-mould cleaner, and if there are any stains left by the damp and mould you can ensure these don’t show through the new decoration by painting on an anti-stain primer first.

If the plaster is not sound, you will need to hack if off and then treat the underlying surface with a salt neutraliser and fit a mesh membrane to the wall before re-plastering if the salt deposits are heavy (products to do so are mentioned above).

If you find that you do not have any ventilation in your chimney (either top or bottom or both) then you will need to add some, in the form of cowls for your chimney top and air bricks inserted into your wall in front of your fireplace if you have a blocked up fireplace.

You should aim to insert your airbrick in the wall on the ground floor about 300mm up from the floor.

If you have a suspended floor with a void underneath it may be best to position the vent under the floor as this will help to prevent draughts in room spaces (ensure the void beneath the floor itself is also ventilated via air bricks in the external walls).

In terms of top ventilation, an air brick should be inserted towards the top of the chimney breast on the outside wall of the property to allow any cold air to ventilate outwards.

If your chimney pots are capped, you should replace the caps with cowls – these are ventilated caps that don’t allow rain to enter but still allow air to enter and leave. Cowls are available in a wide variety of styles and in different materials such as metal and clay.

With the ventilation issues sorted you will have to dry the damaged area out properly – this may take some time.

Remove any wallpaper that may be covering the damaged area and assess the condition of the plaster. If the damage is not too bad then you can cover it with a damp and stain blocking paint (suitable product mentioned above) and then redecorate over the top.

If the plaster is too far gone then any damage will need to be hacked off and replaced with new plaster. Again if salts are present, treat with a salt neutraliser and add a membrane if necessary.

Damp, mould, staining and salt issues can be a real nightmare and cause unsightly stains and patches in your home. Fortunately if you catch them early enough, they can be easy to resolve yourself but if not they can take a little more work.

Which ever situation you find yourself in be assures that any issues can be resolved in a straight forward manner and leave you with a dry and healthy home.

All project content written and produced by Mike Edwards, founder of DIY Doctor and industry expert in building technology.