Keep it natural

Natural Materials as a System for Sustainable Building by David Kitching of Natural Deco Ltd.

What is sustainability? According to the United Nations, it’s a way of using Natural resources such that those resources remain available for future generations. A dictionary definition is ‘to hold up under, withstand’. In development theory, sustainability should be assessed from economic, a social and environmental perspectives.

So within the context of a building, we might say that sustainable construction is that which uses materials that are resilient, strong and serve their purpose, that are economically efficient by virtue of their cost or their longevity, that are conducive to a pleasant and healthy living environment and that have minimal environmental impacts in their recovery, manufacture, use or disposal.

A building structure is a complex entity and is called upon to fulfil a number of sometimes contradictory functions.

Consider an external wall for example. Very simply, it may comprise a number of layers;

exterior paint

exterior render

bricks, stone or timber core structure

interior plaster

interior paint

Together, these components have to work to hold back rain, cold and heat from outside whilst helping to maintain a relatively constant temperature and humidity on the interior face. Meanwhile, this wall is rooted in the ground which can be moist or dry and which can subject the wall to movement and subsequent structural strain and distortion.

 How can a wall reliably fulfil its role whilst also fulfilling our sustainability objectives? 

Exterior

Let’s consider the structure of a wall from the outside first. Since about the 1950’s, paint has usually been made from petro chemicals and acrylics. The advent of these enabled two methods of combating the elements; seal the wall entirely by providing an impermeable layer using these new paints, thereby maximising runoff. Or enable the wall to take up a degree of moisture through porosity in the paint and Natural capillary action of the substrate, using more traditional paints that were vapour permeable and allowed the moisture to pass out again in drier conditions. In fact the former became the default practice.

Walls are systems. Their components are interdependent. Painting their exterior face with non-permeable paints has ramifications for other parts of the structure. The efficacy of synthetic and acrylic paints in sealing a wall against water depends upon the integrity of the underlying render, if there is one, and how well any points of entry for water have been blocked. Because they sit on top of the substrate to which they’re applied, as a sort of separate ‘render’ in their own right, they also depend on their resistance to cracking and splitting. Once a fracture occurs, water can get trapped behind the paint and both lift it away and saturate the underlying substrate, causing damp. It may also cause damage to the core structure of the wall – renders, mortars, brick and stone – as the trapped water freezes in cold conditions and expands to cause cracks. Any ‘breathability’, or vapour permeability, in an underlying render or the structure of the wall itself is compromised by it having been sealed with the paint.

Where moisture is rising up a wall from the ground, the wall needs to allow that moisture to migrate out into the air. Where a latex paint has been used, this is not possible and so the moisture will accumulate in the wall as damp. 

Damp will reduce the thermal resistance or U value of the wall. It can also damage structural components and create risks to health by encouraging the growth of moulds and fungus. Where there is no wall cavity or the cavity is bridged with ties or insulation, damp can migrate to internal walls. Where the cavity insulation has low hygroscopic properties and doesn’t absorb moisture, as is the case with fibreglass or mineral wool, the moisture instead reduces the thermal insulting properties of the cavity by bridging through the air. However, where the insulation tends to absorb moisture, as is the case with Natural fibre insulation such as hemp or wool, it’s able to prevent the transition of moisture to internal walls so helping to maintain the U value of the wall. Whilst it’s true that Natural insulation that has absorbed moisture has a reduced thermal resistance, it makes up for this by releasing latent heat, acquired during the absorption process, when it dries.

In short, where exterior paint is being relied upon to provide a non-permeable barrier to rain, there is a risk of trapping moisture that can severelydamage the structural integrity of a wall, cause damp and undermine the ability of a wall to fulfil its main functions of protecting from the elements whilst maintaining an agreeable interior surface and atmosphere.

A Natural alternative to conventional paints, based on the traditional versions but benefiting these days from much development in modern laboratories, is Silicate Paint or clear hydrophobing agents, such as those manufactured by Beeck GmbH of Germany. Because they comprise the same mineral components of which the render, brick, stone or other substrate is usually made, they bond both chemically [termed silicification] and physically with a wall, so they can’t lift off. Think of it as being more like ‘staining’ the substrate rather than forming a separate plastic layer as is the case with synthetic dispersion paints. They also line the pores rather than blocking them, thereby allowing the movement of moisture out of the wall. Which is why they’re described as ‘breathable paints’.

Silicate paints are free of any artificial resins, solvents and biocides and they don’t give off toxic gasses in a fire. Unlike etro chemical paints they’re made from quartz sand and potash, both hugely abundant minerals and, when they do degrade they simply re-enter the normal ecological cycle. Any waste by-products of their manufacture are composted or recycled.

Silicate paints are suitable for interior or exterior use in domestic or public buildings, especially hospitals and schools where is resilience is particularly important. Because they bond with their ubstrate, they are an effective anti graffiti paint as they can be scrubbed with cleaners. In older period buildings such as country houses and churches, their breathable properties help to preserve the fabric of the building and also lend themselves to the traditional ethos of conservation. They contain relatively little embodied energy, are incredibly durable and their permeability can help in energy efficiency by helping to regulate temperature and humidity. They have a pleasant matt finish and they’re often used for decorative applications. And they come in an enormous range of colours, all using Natural pigments.

Of course, the abilities of a breathable paint to be permeable to moisture is limited if it’s applied to a non or poorly permeable render. How many oldstone cottages now suffer from damp and structural degradation because of the application of concrete or cement render to their outside? Lime plaster is a traditional solution but, although it has a mostly well deserved reputation for being carbon neutral, this is dependent upon the efficiency of the burning process. An inefficient kiln will create far more CO2 than an efficient one. 

Lime is also dangerous and difficult to work with and, whilst it is breathable and flexible, it requires professional skills and isn’t always appropriate for new build or modern contexts.

There are Natural alternatives of course. Such as silicate plasters again manufactured by Beeck. Made from potash waterglass, barite, marble powder and cellulose fibres, these do contain a small percentage [less than 2.5%] of a synthetic resin to act as a stabiliser but otherwise it is again a sustainable product, just like the paints. Furthermore, it comes with various grain sizes, is fully breathable whilst being actively water repellent and canbe coloured to any tone. It’s extremely hard wearing and is also suitable for interior use. 

Interior

There’s a greater likelihood that moisture will be trying to migrate through a wall from the inside to the outside rather than the other way round. This is because human activities in the house can create more moisture which will tend to move through the wall down a ‘moisture gradient’ to drier areas.

On internal walls, common practice is also to use non-permeable, synthetic resin dispersion paints or acrylics, often referred to as ‘lining a room with a plastic bag’. The reason for this apt analogy is of course the paints complete lack of breathability.  The result encourages condensation, precludesthe absorption and dispersion of airborne moisture produced as a by-product of normal living and fails to allow walls to perform a humidity and temperature regulating role of which they should be quite capable.

Apart from the structural implications already discussed, sealing walls in this way also encourages the retention of the toxic fumes that offgas as Non Methane Volatile Organic Compounds [VOC’s] from such paint. The smell of conventional paint for example is produced by dibutyl and diethyl phthalate that take time to evaporate and is the cause of countless headaches for many. Some of the chemicals involved in the pigments, binders, and carriers of modern paint manufacture include petrochemicals, solvents, mercury, formaldehyde, benzene, xylene, defoamers, preservatives and other sundry chemicals. Additionally, cadmium and chromium can often be found in the pigments. The health implications of other offgassed compounds is still poorly understood but the risks are sufficient for the World Health Organisation [WHO] to have classified painting and decorating as a ‘hazardous occupation’, specifically identifying the carcinogenic risks, reporting a 40% increase in lung cancer incidence amongst regular users ofmodern paint.

US Environment Protection Agency (EPA) studies indicate that concentrations of VOC’s are consistently ten times higher indoors than outdoors, with numbers rising to 1,000 times higher after a new coat of paint. A report by the American Lung Association states that VOC’s can produce a number of physical problems such as: eye and skin irritation, lung and breathing problems, headaches, nausea, muscle weakness and liver and kidney damage.

Allergies and chemical intolerance are on the increase. And paint may be a factor in this. Research conducted at the University of Western Australia and published in the British Medical Journal for example, indicates a link between paint derived air pollution and the dramatic increase in asthma amongst children over the last four decades – curiously, about as long as petro chemical paints have been in widespread use. 

Other research in the States has found that VOC’s are partly responsible for the creation of smog, increasing levels of tropospheric ozone and thereby contributing indirectly to global warming.

The manufacture of petro chemical based paints is part of an industry that is itself unsustainable and which relies on finite resources. Paint manufacture causes a great deal of pollution and creates non biodegradable waste many times the volume of paint manufactured. The EPA has categorised paint as a foremost environmental hazard. The paint is not biodegradable or recyclable and it sits outside of any natural ecological cycle. It contains a large amount of embodied energy and it off gasses a range of toxic fumes that damage our health and contribute further to environmental degradation. Hardly a sustainable building material.

 Comparison between ecological cycles of natural and synthetic paints

A Natural equivalent of these paints is Natural Resin dispersion paint such as those manufactured by Auro or Aglaia, both again of Germany. These paints are also fully breathable and are made from sustainably produced natural resources such as plant cellulose, quartz, chalk, citrus and linseed oil and tap water. Auro, for example, grow many of their materials close to the factory on organic farms and power their factory entirely on renewable energy. Such fastidious attention to detail is reflected in the quality of the end product.

Nature, of course, is not always benign and Natural paints can also offgas fumes and VOCs. But they do so to a lesser degree and for a shorter period of time. And would you rather sniff petrol fumes or those from orange oil such as is deliberately inhaled as part of any aromatherapy practice? It seems intuitive that our bodies can cope with the latter but have not developed to cope with the former. Were you to take a walk in the woods, you’d be surrounded by these natural VOCs. Many, even most, Natural paints are solvent free anyway and so VOCs of any sort are less of an issue with them.

All the ingredients that go into making these paints are fully declared and available for perusal by users. So in the unlikely event of anyone suffering an allergic reaction to them, they at least stand a chance of finding out what it is that they’re reacting to. Conversely, they can avoid paints that contain materials that they know they’re allergic to.

Again, like their exterior counterparts, the ability of these paints to pass water vapour and moisture is restricted if the underlying plaster is not itself breathable. Most internal walls are lined with gypsum plaster or plasterboard containing gypsum.

Gypsum itself is fairly benign environmentally and health wise.  It is an evaporite deposit. In other words, it’s formed geologically by stranded seas evaporating and leaving behind all the minerals contained in sea water. Consequently, gypsum plaster contains, or comprises, a lot of salts!  Gypsum itself is Calcium Sulphate and if it becomes damp then the sulphates can become mobilised and can cause serious problems in a building, attacking the building fabric, blistering off paint and causing efflorescence, or the deposition of white fluffy mineral salts on the surface. 

Here’s further reason for being concerned about the penetrating damp issue referred to earlier. And it’s another benefit of breathable interior paints in that they allow moisture to evaporate away rather than building up and dissolving the salts in the gypsum.

Of course, it’s common practice to prime gypsum before painting over it to control the suction when painting, and it acts a bit like a sealer for the plasterboard. Unfortunately, PVA is often used which inhibits gypsums otherwise natural ability to breathe. Not that it matters anyway if one is using acrylic or petro chemical paints to inadvertently seal it with. Needless to say, natural primers are fully breathable, just like their top coats.

Gypsum is often recovered through a process known as strip mining which basically involves ripping the top layers off a wide swathe of land, destroying any Natural habitat in the process. Of course, the mining companies try to put things back the way they were, planting trees and suchlike, but the normal ecology of the area involved is severly damaged or destroyed.

A Natural alternative to gypsum is a range of plasters, made by Aglaia, based on beech cellulose, water, chalk, titanium dioxide [as used in most paints, Natural or otherwise, as a pigment] and less than 1% boric salts.  This plaster is not only breathable but actively absorbs humidity as well as airborne pollutants, is flexible and can be tinted to any colour or painted. 

Again, it fulfils almost to the letter, all the sustainability criteria mentioned earlier.

Summary

It’s worth noting that amongst the manufacturers seeking to exploit this new market for sustainably produced products, paints especially, there exists a few villains of the peace, intentional or otherwise. Just because a paint is described as Natural or organic, or even eco-friendly or ‘green’, does not guarantee its credentials. Often, paints described as such are actually based on acrylic emulsions. They usually offer some advantage over conventional paints but if there isn’t a full declaration of ingredients available then it’s probably safe to assume the worst. ‘Organic’, after all, refers to the chemistry of hydrocarbons of which mineral oil is an example!

Genuinely Natural paints and plasters, and even insulation, are not a panacea. What is? As long as we need wall coatings and building materials that perform to the standards that we have come to expect, we have to play some clever games with chemistry. But Natural paints, as opposed to the petro chemical versions that we have all fallen into the habit of using, create healthier living spaces, are better for buildings, generate less waste, embody less energy, are largely derived from renewable resources and, on virtually every count, fulfil the sustainability criteria outlined earlier.

The displacement of breathable paints and other products, made from traditional constituents and in use for centuries, by plastic versions over the last 50 years has engendered a great deal of ignorance and prejudice about these materials. It’s assumed that ‘traditional’ means old fashioned and inefficient. In fact, modern Natural emulsions, glazes, metal paints, varnishes and insulation represent a synergy of state of the art chemistry and chemical laboratories with a sound environmental ethos and materials that nature readily makes available. Traditional materials have been tried and tested over generations whereas modern acrylic and cement paints have had just 50 years to prove themselves and have shown themselves to be inadequate, unhealthy and environmentally dangerous.

If we’re truly interested in making our buildings and living spaces more sustainable, by every criteria that that word implies, perhaps it’s time to reconsider the love affair with petro chemicals that permeates our society, consolidate our knowledge and look again at what nature offers us. Our health and that of the natural world as a whole, not to mention our buildings, may benefit greatly as a result.

You can learn more about the products mentioned in this article at www.naturaldeco.co.uk .