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Breathable Paints Explained

What are breathable paints?

The term breathable is everywhere, from nail polish through to clothing. The dictionary defines breathable under two definitions –

  1. Suitable or pleasant for breathing
  2. Permitting air to pass through

This is an extremely varied definition, on the one hand it means that air or moisture can pass through a material, on the other it means that a material is safe for humans to use. The wide scope and interpretation of this term has led to confusion, what exactly constitutes a breathable paint?

For building physics we class a breathable paint as a material that will allow the water vapour to permeate, travel or transfer through itself. The basic premise of a truly breathable paint is its ability to allow water vapour to evaporate from the surface and not prevent this transfer to be slowed or stopped entirely.

Great, we have defined a breathable paint in its basic form, but we are still left with a serious issue; a lot of paints on today’s market state to breathable, how do we know what is best? How breathable are they? As they state they are breathable does this mean safe to breath or they allow moisture to pass through them?

There is no defined European Standard as to what constitutes breathability and there are at least 8 different ways to measure the breathability of a material.

Until the industry adopts a defined standard this will always be an issue, however when it comes to paint the most accepted and adopted standard is SD Value, it helps that it is probably the easiest to understand, interpret and compare.

SD Value is a German method, although it used throughout Europe, and it stands for steam diffusion or air layer equivalence. It is a measure of how much of a barrier a paint coating is to water vapour and how easily the vapour can pass through this barrier, it is measured in meters. The lower the SD Value means that more moisture is able to pass through, the higher the SD Value, the lower the moisture transfer.

A truly breathable paint should have an SD Value ranging from 0.01 to 0.5. This equates to moisture having to travel 1cm to 50cm to pass through the paint, meaning it has very little resistance and can pass freely without being slowed or stopped. Conventional masonry paints will likely have an SD Value of 1 or above. This equates to moisture having to travel through the equivalent of 1 metre of air to escape.

The vast majority of paints can technically be classed as “breathable”, as they will eventually allow some moisture to escape. However, it is the rate of transfer or the distance which constitutes a truly breathable paint.

If you were to look at one of our paints you will always be able to find the SD Value and this is regardless of the brand, in fact if you look at competitors’ products they usually always state the SD Value of their paints, because they know they are offering a truly breathable paint. However, if you were to look at a conventional emulsion or masonry paint that states it is breathable, there is no SD Value to be seen, this can usually be taken as a clear sign that this paint will not allow for the free passage of moisture, otherwise the SD Value would be there. Most “breathable” paints that do not state there SD Value usually fall in the class of the first definition of breathability; they are suitable to be breathed, meaning they won’t necessarily harm us, or they are technically breathable, but simply won’t allow high levels of moisture to transfer freely.

Why use breathable paints for historic buildings?

Older buildings are fairly simple in construction, they usually comprise of thick and solid walls, with no cavity. The result of this construction method means that moisture will always be, in some form, present within the building fabric. The original material (Lime Mortar made from Lime Putty) uses to create these buildings were relatively simple too; they were softer than the host material (i.e. Stone) and they allowed moisture to escape and not become trapped.

Damp is commonly found in older buildings. Up until recently it was (and unfortunately by some it still is) believed that the only way to eradicate this issue was to waterproof the entire building with a waterproof coating such as modern masonry paint or by injecting damp proof courses with the aim to stop water penetrating the building. Whilst this offered a temporary solution it was and is still not the answer, with the majority of these applications ultimately failing.

One of the main reasons for this failure is that a building can undergo significant movement, both structurally and thermally. Once a crack appears water can penetrate the crack and be held within the wall behind the non-breathable or waterproof coating, which can include cement and paint. A secondary issue with cracking is during the winter or colder months, as water freezes it has an expansion rate of roughly 9% per freeze. As this freeze and thaw cycle is repeated when we reach certain temperatures, the cracks are able to increase and widen in size, which allows further water to ingress with no means of escape.

A build-up of moisture can lead to damp within the walls which may cause ‘blistering’ and ‘bubbling’ of the paint where the water is trying to escape, this is referred to as hydraulic pressure. In more serious cases the render may be ‘blown’ or forced off by the pressure of the trapped water.

Water that is trapped within a wall can lead to serious deterioration of the building fabric. Any non-breathable paint applied to the building will act like a film around its surface. If you imagine wrapping your walls and ceilings in cling film, this will stop the moisture from going in and out but will trap it and the water will build up within the surface. This is where the term “film-forming” paint comes from as it seals the building and stops the building from breathing and allowing moisture out of the walls.

The reason that modern paints such as emulsions and masonry paints are classified as film forming is due to the chemicals that are used, which create a plastic like layer, enabling them to sit on the surface of a wall or ceiling.

This leads us back to the issue with defining breathable paints: You can wrap your face in cling film and poke a hole where your mouth is, you can still breathe, but you aren’t going to live very long.

To put it simply, the most appropriate paint for historic fabric is one that has a low SD Value.

Why use breathable paint for contemporary and new build construction?

Paints are everywhere, both internally and externally. Most modern paints are comprised of pigments, binders and solvents, however the majority of these components are derived from petrochemicals. The use of petrochemicals has a negative impact on both our health and environment. The use of crude oil to create these materials can lead to the creation of harmful toxic waste.

In 1989 the World Health Organisation reported that painting is an occupation that is classified as carcinogenic due to the extensive use of chemicals that are contained within paints. Further studies have shown the indoor air environment can be 10 times more polluted than the external environment, which is again caused by the extensive chemical additions found in materials such as modern paint. We spend up to 80% of our lives inside buildings, where up to 90% of the internal surface can be covered in some form of petrochemical coating. Due to the chemical additions contained within these paints they become very wasteful, in some cases these materials can produce up to 10 times their weight in waste. In the UK 385 million tonne of paint is sold yearly. A further issue is that the chemical additions make recycling the paint very difficult, with the majority of discarded paint being sent to landfill.

We only stock naturally produced paints, that have minimal to no chemical additions depending on the type and brand. This allows us to supply paints that have no detrimental impact on the environment, the applicator or the end user.

For example, the Aglaia range of paints are made using renewable and recycled crop sources, where all of the manufacturing waste goes to a community composting facility, Aglaia is a truly sustainable paint. Unlike modern petrochemical based paints which produce toxic waste during their manufacture and once applied release dangerous and volatile organic compounds (VOCs) that can have an adverse impact on our health. Aglaia natural paints are non-carcinogenic and do not encourage allergic reactions as they contain no synthetic chemicals, which also reduces dust build up.

Breathable paints are often seen as something that are only suitable for older building, this is not the case. Breathability is also an important factor within modern buildings. By using a breathable paint internally, you can help regulate the internal environment and air quality. Breathable paints can absorb moisture and release it again, meaning when humidity is high the paint can take moisture from the air and release it back when the humidity drops, which helps maintain a healthy environment and acts like a natural dehumidifier.

Types of breathable paints?

We offer all types of paints for both internal and external applications. The most commonly known is Limewash which consists of burnt limestone and water. When applied to a porous wall it soaks in, absorbs CO2 and reverts back to limestone. Limewash makes a superb internal and external coating and can be coloured using Pigments.

As a derivative of limewash we also supply Lime Paint which comes in a powder form ready to mix with water. Lime paint can be supplied in 19 different colours and although it contains around 3% acrylic to aid dusting and adhesion it still retains a low Sd value and is highly suited to lime rendered buildings both internal and external.

Beeck Mineral Silicate Paints were developed at the end of the 19th century and, as with limewash, the mineral paints soak into the background and bond to it. Where they differ is that limewash generally bonds to the calcium in the background whereas mineral paints form a strong chemical bond with the silica sand in the stone or render.

It is well known what a strong and stable element silica is and it has been widely used in building due to these attributes. This silica bond makes the paints far more durable than limewash or lime paint, leaving the paint attached to the substrate. The way the paint bonds to the surface also gives it extreme durability as the chemical bond achieved means that it cannot be stripped by paint strippers.

Externally the Beeck Mineral Paints contain a hydrophobe, which repels water from the surface, without having any impact on the breathability of the coating, which adds further protection for the underlying surface.

Mineral paints also offer much greater longevity compared to limewash and lime paint due to the bond with the surface, they are also non-flammable along with many other benefits depending on what type of mineral paint that is used. They can be mixed to over 300 colours.

Aglaia Natural Breathable Paints are manufactured from plant extracts and contain no harmful VOC’s. These can be applied internally just like a “normal” emulsion paint and are suitable for lime rendered as well as cement rendered walls. Aglaia Breathable Paints are manufactured from only natural ingredients making them environmentally friendly. They use only renewable sources and no petro-chemicals (synthetics), this means they are friendly to people with allergies. Due to their natural makeup they also do not attract dust build up on the surfaces and can be cleaned with water.

We are stockists for Earthborn who supply a range of breathable claypaints and emulsions.

Further information including technical data, colour cards and information can be found in our pdf library or by contacting us either by email or telephone.

17 thoughts on “Breathable Paints Explained”

  • Chris Mitchell

    Dear Sir or Madam,

    I live in Norfolk and have an old barn near the coast (about 500 meters: I only mention this as salt mist may be relevant to the discussion). The barn is built with quite soft Norfolk brick and lime mortar. some are quite crumbly. I will be repairing the building over the next 3 years, replacing some brick, where they have determinate do away and reprinting with hydraulic lime mortar.

    my question is that much of the building will still want to absorbe a lot of water as the old bricks are so soft, so is there a solution I can use that's 'clear' so as to create a bonded layer over the brick surface (and mortar) to protect them from further water and frost damage yet maintaining it to pass the maximum amount of water vapour. I do not want to trap moister in the building fabric.

    Your advice will be most welcome.


    • Adam Brown

      Dear Chris

      Apologies for my delay in reply, our website has recently undergone some changes and i now have access to the comments section.

      We do have a vapour permeable, protective coating that can be applied - Beeck SP Plus .

      However, as every application is unique i would recommend that you contact us on 01208 79779 and we can discuss your application and requirements in more detail.

      Kind Regards

      Adam Brown

  • Paul Taylor


    I was wondering if you could tell me how to prepare an exterior lime render house?

    I know you need to apply a lime wash first, but I want to know the best ways to apply the lime wash, the duration of times between coats and wether you need to apply a stabiliser before your 2 coats of breathable paint? ... if you could give us a step by step guide on the correct method to use is appreciate it!

    Kind regards

    • Adam Brown

      Hi Paul

      Render applications can vary depending on the type of mortar, the finish you are looking to achieve, the host surface and also the location/exposure of the building.

      We do have some general guidelines on the website, however i would advise that you contact us on 01208 79779 and we can discuss the specific requirements for your application.

      Kind Regards

      Adam Brown

  • Michelle Kennedy

    Dear Adam, thank you for your very informative article on breathable paints. We have a house with lime plaster internally and a Dulux vinyl Matt undercoat has been put on. Dulux have said it is breathable with an SD of < 0.03. Should this be acceptable or is it impossible to have vinyl breathable paint with a low SD? We are considering trying to take it off. Thank you, Michelle.

    • Cornish Lime

      Dear Michelle

      I would be quite surprised if a vinyl matt had such a low SD value, especially as low as 0.03. Have they provided any documentation to state this? Also it is worth checking that if the SD value is just for the undercoat or is it for the paint itself?

      An SD value of 0.03 would be suitable for a lime plaster

      If you have any questions please contact me on 01208 79779 or via email -

  • Anne Clarke

    How can I tell the difference between Lime and ordinary masonry paint once it has been applied to external walls?

    • Adam Brown


      There is no defined way of telling the difference. However, there are a few tell tale signs that you could look for.

      Firstly masonry paint can look like a plastic coating and have a sheen. It is usually quite smooth and feels plastic when you rub against it.
      It can also be prone to cracking, these are usually very fine and will show up if you spray water over the wall. It is also prone to bubbling or peeling off the wall.

      A lime wash is usually quite dusty and can be brushed off the wall if rubbed forcefully enough.
      Lime wash will also change colour when it is wet, it usually goes darker and you can see it dry out.

      One way of telling the difference is to remove some of the paint from the surface. A masonry paint will likely come off in sheets due to its plastic content.

      If you would like to discuss this in more detail, please call us on 01208 79779.

  • Norm Pettigrew

    Breathable paint is the only type to use on old clay tile foundation blocks. The waterproof paints end up damaging the clay tile blocks.

  • Craig Mackay

    Hello, i have the ‘blistering’ and ‘bubbling' problem on our 17th c house internal walls. Couple of questions:

    1) How do you prepare the wall to remove or paint over existing normal paint finish (eg. can i just lightly sand an paint over with earthborn for example?)

    2) How does earthborn compare to the other paints you mention? I dont know if the plaster is lime or not, is it suitable for covering either way?

    3) What advice do you have for bathrooms with very high humidity? To block the moisture going in with normal bathroom paints or to stay breathable and allow high humidity in?

    Thank you for any advice



    • Adam Brown

      Hi Craig

      Blistering and bubbling of the paint film is usually an indicator that there is moisture held within the substrate, this would suggest that the plaster has some level of permeability, so a breathable paint will likely help.

      To answer your questions -
      1) In terms of preparation there are several different methods. I would start by trying to peel and scrape back the failed areas and you may find that the paint removes with relative ease. From there sanding the surface may remove some of the more stubborn areas, however i would recommend that extra care is taken here as the sanding could damage the underlying plaster. If this these options do not address the issue you could look to use some form of paint stripper, we stock an environmentally friendly range of paint removal products - Scheidel. I would advise that the first two options are attempted to begin with, as they cost very little apart from your time. The majority of our internal paints can be applied over existing paint finishes, however a breathable paint is only as good as the surface it is applied too, so the problem could still persist.

      2) The Earthborn paints are very good paints, easy to use and suitable for both lime and modern plasters. All of our internal paints are relatively easy to use and they are all environmentally friendly alternatives to modern coatings. In terms of 'Eco credentials' the Aglaia range is probably the best, it is made exclusively from recycled and renewable crops, although both the Beeck and Earthborn are close. In terms of performance, longevity and vapour permeability we would advise the Beeck range, we have full performance data and have been supplying these for over 15 years. Every range we stock has paints that can be applied over numerous substrates, Earthborn and Aglaia will cover gypsum, lime and existing paint, within the Beeck range we would recommend using the Maxol as this can cover different backgrounds, as well as offering the highest vapour permeability.

      3) In terms of high humidity areas this is not always straightforward. Firstly ventilation is key to deal with high humidity. Secondly the paint can help combat the issue of high humidity, but you will also need to rely on a suitable plaster. if the wall is vapour permeable (plaster, paint etc.) it will be capable of holding excess moisture when humidity rises and then release it again when the humidity lowers. Bathrooms are always problematic as the humidity is not constant and will always fluctuate. One common issue that can be found in bathrooms in all houses (new or old) is mould, the main cause is lack of ventilation, but the paint and plaster can also further the issue. If a surface is closed and unable to absorb and release moisture, it will allow condensation to form on the surface, if this is combined with a food source (usually dust) and then sufficient humidity, mould will form. If the wall is vapour permeable, this problem can be reduced. Also modern paints, especially bathroom paints, tend to contain higher chemical additions which can produce electrostatic charges, which in turn attracts dust, which is a food source for moulds. We wouldn't recommend the use of Earthborn or Aglaia within a bathroom, but the Beeck range is perfectly suited to these constant moisture changes and can help address potential issues.

      If you would like to give us a call on 01208 79779 we can discuss your applications in more detail.

      • Craig

        Thank you for your excellent reply above, looking at your Beeck page it states they are "only suited to a render that has not yet been painted", as it's an existing bathroom I'm guessing this is a problem?

        Also, do you recommend using Earthborn Wall Glaze before painting to stabilise sandy, powdery interior surface, again another sign of damp?

        Thank you


        • Adam Brown

          In regards to the “only suited to a render that has not yet been painted” - This relates to the Beeckosil system, which is one of the external paints they produce. The Maxol interior paint will work fine over existing painted surfaces. However, as i mentioned in my previous post it is all dependant on the existing make up of the wall as to how well any of these paints will perform.

          The wall glaze may help with crumbling plaster. Again it depends on the type of plaster - if you have gypsum plaster this is a sign of moisture breaking down the plaster and the glaze may not be able to stabilise the plaster. If the plaster is lime based, i would recommend using the Beeck Fixative, Fixative is the reactive component for the mineral paint systems and can be used to bind crumbling stone and lime plasters. We have used this successfully for several years.

          Any questions please contact me.

  • Ursula Mort

    We are in the process of exposing a sandstone wall in our living room. We'd like it to remain exposed but to paint it white. What would you advise -we don't want to seal as it as we want the wall to breath. What advice would you give regarding the paint we should use? I read somewhere using limewash on sandstone where it's not been used before can cause deterioration. Is it ok to paint without sealing the wall? Thanks.

    • Adam Brown

      Hi Ursula

      In regards to painting an exposed sandstone it has been stated that lime wash to an unpainted sand stone surface can cause deterioration. I would recommend the use of Beeck, Aglaia or Earthborn interior paint. These are all vapour permeable and will not seal the surface.

      For exposed mansonry we do favour the Beeck internal paint systems as they chemically bind to the surface, which offers excellent longevity and vapour permeability and can help stabilise the stone if it is crumbling.

      I would recommend that the surface is thoroughly cleaned down and any coatings removed, then 1 coat of Beeck Fixative (as a primer), followed by 1 or 2 coats of Beeck Maxol.

      If you wish to discuss this in more detail or have any questions, please contact us on 01208 79779.

  • Robert Hayden

    First, I must say its most helpful having all your 'posts' to read - as even though they are not my issues/situation they give one a greater understanding of different building problems (relating to build material/ paint surfaces/ past experiences/ best practice, etc), and the possible options & remedies open to each scenario.
    So, with this in mind that other may read my paint dilemma – could I seek your advice ? !

    My house is circa-1600 cob wall thatch house. It has for past 100yrs been owned and maintained by the MOD --and appears to have been ‘repaired’ & maintained to varying standards depending upon the materials available at the time, the money (cheapest) available to spend, and the vagaries of repair options & paint choice, depending upon the individual employed at the time (traditionalist or quick-win modernist) !

    I have just installed some new oak windows and so re-made the walls...which are in need of a re-paint (last done 20+yrs ago). So what paint to use ? !
    1. The base of all walls appears to be primarily flint (on no foundations) with lime mortar -- presently painted with a black (bitumen type ?) painted skirt. When the wall dry's out I can clearly see damp darker blotchy patches over many parts of the wall.
    2. In places the wall has sections of brick (no DPC) & lime type wet crumbly mortar (can be picked out easily with a finger-nail) --presumably not original and put in to strengthen & reinforce the cob-wall (which is 22inches thick).
    3. On the gable end (replaced window end) -- half of the first floor wall is merely a wooden frame-work covered in lathe & plaster over-rendered in concrete (being just a 2 inches thick skin) - -the other half is cob. I presume the cob-wall previously went to the roof, but was removed to install this window when the house was 'modernised' in 1960s. The ground floor is totally brick over the cob.
    4. The other gable end wall is completely covered in 1-2inch thick concrete/pebble render - - which presumably encases the old cob-wall and strengthens it (though it could be brick behind it). Like the other end a window has been placed on the first floor - -and similarly the wall above it is just 2 inches thick.
    5. The front of the house is a mix of standard cob-wall, sections of brick, and areas of concrete render. When humidity conditions are high (on a hot day) a thick sticky ooze runs out of the wall down my windows (presumably some previous paint undercoat sealant system).
    6. All of the house back wall appears to be the original cob. . . but only 30% is exposed. The remaining 70% of the wall is internal: being attached to a single storey brick extension with no DPC & lower ground level internally. Therefore, it has its own problems with 40% of the paint & mortar missing, but this is understandable given its appalling design/construction . . .so any paint solution would never last !
    7. Internally, all walls have been re-lined with 2inch blocks & a plastic sheet ...and interestingly I can see that the cavities are wall-papered ! Damp and condensation are a continuous battle ...but restricted of course to the external walls.
    8. From my experience & your web-site advice sections ...I would say all external walls are painted with modern masonry paint, as it appears to be a thick plastic-type layer that can be peeled off. If viewed on the side it appears very shiny (tiny reflective specks) and repels water well. Paint on the render zones is 'as new' and only in need of light touch-up. The paint on the bricks is falling off in vast patches being pushed out by the damp mortar. Most of the flint zones are similarly patched with 40% pushed out at the mortar joints. Leaving the cob-wall condition somewhere in between....generally sound with isolated minor lifting patches.

    So in short, all the damaged paintwork is at the mortar joints the brickwork and in the flint base. Given my wall is already painted (i.e. sealed) and would take many hours/weeks to strip off - - i can see little benefit of over-painting with your ‘breathable’ paint. And as the majority of lime mortar joints are so soft, damp & friable (and in places totally absent with gaps =mice ingress points) i am tempted to re-point the flint with ordinary hard mortar..inject some Dry-Zone...then cover with one of your breathable paints. My thoughts being; concentrate on the lower damp level /install hard mortar & flint chips to seal the ground-level area & prevent rodent attack / wire brush prep the entire black surface (likely i would break into existing paint surface) .... .then finish with your breathable /waterproof paint to help the moisture escape.
    But for the rest of the house— the ‘modern’ paint is generally sound/i cannot easily strip it off/ the walls look acceptable above 4 ft make good the brick mortar joints (with ?), and just paint the rest of the house with standard (cheap) masonry paint !

    Apologies for the long description, but the more words i put down the more i realised i have been putting this task off for so long due to my quandary ! Can you help /advise ?

    • Adam Brown

      Hi Robert

      Firstly i apologise for the delayed response.

      It sounds like you have a number of potential issues that are causing damage and/or damp build up. Having read through your explanation, there are several ways to tackle these problems, however to truly address the issues you would likely be looking at extensive work. Which I think would be best discussed over the phone or face to face as there is not a one size fits all approach unfortunately.

      To answer your summary at the end, i would offer the following -

      Clearly the building has been touched up/repaired over the years with inappropriate materials that are causing problems. It doesn't surprise me in any way that the majority of the damage is taking place at the mortar joints. These are often referred to as the evaporation zones, where the weaker mortar (compared to the brick) can enable the escape of moisture from within the fabric. Firstly i would not be recommend re-pointing in 'hard cement' mortar or using Dry Zone. This is just going to further trap moisture within the fabric, it will also seal the joints and further close down areas where moisture is trying to escape from. I would recommend re-pointing the joints with a lime based mortar, these areas (with appropriate paint) will then allow a point where moisture can escape and whilst it may not solve the overall issues, it will certainly offer the moisture a small route of escape. Strength and sealing are often seen as the answer, however a NHL based mortar (be it site mix or the Cornerstone ready mix range) will offer a reasonable strength and when combined with a mineral paint should prevent rodent attack. Whilst cement mortars are extremely hard, a solid wall building is likely to undergo thermal movement, as the cement is very dense it is unable to accommodate this movement leaving it brittle and prone to cracking. When cracking appears, water can be driven into the wall and unable to escape.

      I would recommend that a lime mortar is applied to any area where there is no mortar or where the mortar needs replacing. The areas where you are looking to apply a breathable paint, i would recommend removing any defect paint and cleaning the surface down with a fungicide/biocide and then apply the Beeck Renosil system.

      Given that this is not a straightforward application, if you would like to call us on 01208 79779 we discuss this in more detail.


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