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Contents
• Pigment
• Binder
• Solvent
• Additives
• Alternative paints
• VOCs
• The impact of paint on health
• The impact of paint on the environment
• Legislation and standards
• Specification
Paint has dual role being both decorative and protective. Though usually decorative for interiors, paint's protective features are combined externally in the protection of vulnerable materials such as softwood and metal.
Paint has an impact on the environment during the manufacturing process and on health during its use phase. Unused liquid paint is treated as 'hazardous' and requires appropriate disposal.
Component materials
Most paint is made from three basic ingredients:
1 Pigment - provides colour and opacity
2 Binder - acts like a glue in holding the pigment to the surface
3 Solvent - maintains the pigment and binder in liquid form
Other ingredients include those that prevent bacterial growth, economise the spreading of paint (fillers), thicken paint, prevent 'skin' from forming, enable paint to be easily applied, accelarate/retard drying and prevent foaming.
Paint works by its application to a surface followed by the evaporation of the solvent, thus leaving a film comprising of the pigment and binder.
1 Colouring pigment
Pigments are used to do different jobs in paint including helping to give the film the required properties (Extending pigment) and to increase the impermeability of the film (Barrier pigment), but the foremost is the one providing the permanent colour (Colouring pigment)
White pigment
Titanium Dioxide or TiO2 is used almost universally throughout the paint industry - including both in conventional paints, but also in 'eco' paints. Titanium Dioxide replaced previously well-known white pigments such as Lead Oxide ('Lead White'). Its near universal appeal is derived from its high opacity (the ability to cover or hide). Less-used pigments include chalk and lime, which have very low opacity and therefore can require many coats applied to achieve acceptable opacity.
Titanium Dioxide is made in one of two ways, each of which has a significant environmental impact. (see 'Environmental impacts' below)
Coloured pigments
Pigments are either 'organic' or 'inorganic'. Unless used in quantity, coloured pigments do not provide opacity so most paints rely on their including titanium dioxide.
• 'Organic'. Early organic pigments were based on dyestuffs derived from natural plants. Most contemporary organic pigments are synthesised from coal tar and petroleum distillates, but plant-based pigments continue to feature amongst 'eco' paint brands. Synthetic organic pigments are usually quite brilliant and have good colour strength. However, opacity tends to be low and many organics are not fully solvent resistant.
• 'Inorganic'. The earliest paints used pigments which were obtained by digging certain minerals out of the earth and grinding them to a fine powder. These 'natural' pigments are all inorganic compounds. Typical examples include ochre and sienna. Other inorganic and more prolific pigments in the market are usually metallic oxides derived from iron and clay or synthetics produced from petrochemicals.
2 Binder
In a paint mixture, the binder is responsible for providing adhesion, binding the pigment, and giving the paint resistance properties which make the final coating durable. There are two specific types of binder: oil-based and latex-based.
Oil-Based Binder
Oil-based paint requires a binder that has similar properties to the paint-in this case, the binder oxidizes or dries when exposed to air, hardening along with the rest of the paint.
Binders in oil-based paints are either natural or synthetic. 'Natural' vegetable-based oils include linseed oil, tung oil and soya oil. Today, few paints are made with oil alone. Rather, they are based on modified oils called alkyds. Made from vegetable oils and synthetic resins, alkyds are chemical compounds that dry harder and faster than oils. Nearly all 'oil-based' paints (eg 'gloss') now have alkyds as binders. Exterior oil-based wood primers often are made with a combination of oil and alkyds.
Latex-Based Binder
Latex-based paints actually do not possess latex-rather, the polymer binder that is used creates a film in the paint that resembles natural latex rubber. Almost all water-based paints have a latex-based binder. When the coating is applied, water evaporates from the paint, leaving behind a film of pigment and latex-based binder, which bind together into one continuous coating.
Several polymer types are used as binders in latex paint. The two most common types are 'acrylic', most suitable for exterior use, and 'vinyl acrylic' which though also can be used externally, is mostly applied internally. Other latex binders include styrene-acrylic and terpolymer.
Most modern emulsions are water-based with the latex added to increase durability. The amount of latex determines the degree of sheen seen in matt, eggshell, silk and satin finishes.
3 Solvent
The solvent is the liquid that suspends the other constituents to enable application. Once the paint is applied, the solvent evaporates, allowing the pigment and binder to produce a film of paint (a 'coat').
Solvents are either water or organic. The most common organic solvents, derived from petroleum, are 'white spirit', used in alkyds, and 'mineral turpentine' ('turpentine substitute') used as a paint thinner and for cleaning brushes. Other petroleum-based organic solvents include alkanes (isoparaffins), methyl ethyl ketone (MEK), methylated spirits (mixture of methanol and ethanol), xylene, toluene and acetone. Solvents used in paint that are not petroleum-based include 'gum turpentine and 'citrus oil'.
• It is important to note that most paints described as 'water-based' include small quantities of organic solvents to enhance workability.
Additives
A wide variety of substances are commonly added to paint. These include:
Biocides
The addition of biocides to paint is directed at the prevention of in-can bacterial growth along with fungal and algal growth on paint coatings. Water-based and particularly casein paints are especially vulnerable. By their nature, biocides are toxic and their use is tightly controlled by European legislation, notably the Biocidal Product Directive (BPD).
Prior to legislation biocide formulas were relatively simple but often likely to be hazardous / poisonous (eg mercury and other heavy metal compounds). Post-legislative formulas are more complex as they use a blend of agents to deliver the same effect.
There are very many chemicals available for use as biocides - some of which continue to be the source of concern amongst health campaigners. However, obtaining information about specific formulas is usually difficult: manufacturers of additives regard the information as being commercially sensitive - a situation compounded by the lack of determination of many paint manufacturers to post the contents of their products.
Specifiers who are curious or concerned about additives should quiz the paint manufacturer. There are available a range of responses, only some of which will likely be satisfactory.
Surfactants
Also common in detergents, surfactants reduce the surface tension of water, which in paint allows for easier spreading. Surfactants commonly used in paint have included alkyl phenol ethoxylates (APEs) as well as perfluorinated surfactants, both of which have been largely phased out because of their hazardous nature (endocrine disruption and bioaccumulation, respectively). A new generation of surfactants has now been introduced, members of which are believed to be far less toxic than their predecessors.
Driers
Driers accelerate the drying of organic solvent-based paint by catalysing oxidation. The most common driers are metal and include Cobalt, Manganese, Cerium, Zirconium and Calcium. Concern is expressed about the possible impact of metal driers on health in general, but in particular Cobalt is associated with a range of claims to its hazardous nature including lung, allergy and heart problems synonymous with exposure in production and use 7.
Other types of paint
Drying oils
A 'drying oil' paint is one that, without the use of a solvent, 'dries' through exposure to the air to leave a solid film. There are numerous plant oils that feature in paints, but the most common is linseed oil. Linseed oil paint was commonly used before being replaced by modern alkyd resins and then other binders.
Linseed oil owes its current revival to the absence of organic solvents in linseed oil paint. Typical ingredients are linseed oil combined with zinc oxide (a titanium oxide substitute) and a colouring pigment.
Though arguably safer than contemporary oil-based paint, linseed oil paint is not without its impact on health or the environment. Linseed oil contains a significant degree of embodied energy and emits VOCs - though in very small amounts.
Limewash
Limewash) is the oldest form of 'paint'. The paint is primarily composed of slaked lime (calcium hydroxide) combined traditionally with a low proportion of organic binder such as tallow (or linseed oil). Limewash cures through a reaction with carbon dioxide in the atmosphere to form calcium carbonate in the form of calcite, a reaction known as carbonatation.
Limewash can be coloured through the addition of earth pigments to produce a small range of colours.
Limewash is not particularly durable, particularly in polluted environments where the coating can degrade rapidly.
Health hazards are restricted to irritation on the skin or to the lungs if inhaled - though some sources believe there is also a possible link between 'respirable silica' and cancer, though much more research is required to advance the claim.
Silicate mineral paint
Mineral paints are mineral based coatings formulated with potassium silicate, otherwise known as 'waterglass' as the binder, combined with inorganic, alkaline-resistant pigments.
The paint works by soaking into the underlying material where the potassium silicate binder chemically reacts with the material to form a microcrystalline silicate bond which is insoluble. Secondary crystallisations also take place between the binder, the colour pigment and carbon dioxide in the atmosphere.
Though it can be used on a wider variety of mineral surfaces, silicate paint is particularly effective on render - providing an alternative coating to limewash. Anecdotal evidence from Europe and Scandanavia claim that silicate paint systems can last in excess of 100 years. Pragmatically, though, maintenance should be programmed from 15 years onwards.
Silicate paint is generally a very low toxic (limited to user exposure eyes and skin) paint with raw material, transport and energy as being the minimal environmental impacts.
Distemper paint (aka Protein glue paint)
There are two types of distemper: 'Soft' distemper and 'Oil bound' distemper.
Soft distemper is the forerunner of modern emulsion, It is a water-based paint that primarily comprises a white base pigment such as powdered chalk (calcium carbonate) bound with glue size (gelatin). This basic mix can be tinted with alkali-resistant ('lime-fast') pigments to give a wide range of colours, including blues, greens and various earth tones.
The environmental impact of traditional distemper is limited to raw material extraction (eg chalk) and the production of pigments. However, some modern distempers have replaced the animal glue binder with synthetic glues such as polyvinyl acetate - which effectively renders them as modern vinyl emulsions.
One increasingly popular variant of distemper is 'Clay paint'. This paint is a distemper where the base pigment used is clay powder rather than chalk. Though clay paints boast their 'natural' credentials, specifiers should be aware of contents that can routinely include polyvinyl acetate ('vinegar ester') and methyl cellulose ('cellulose binder') as well as additives familiar in more common paints.
Another variation is 'Casein paint' where the binder used is casein, a milk protein, rather than gelatin. The typical constituents of commercial casein paint are typically chalk, marble, talc, clay and casein. The paint is usually delivered in powder form, requiring the addition of water. Health risks are to the user and are limited to irritation to the skin or lungs.
Caution should be taken when considering the durability of distemper. The paint is easily rubbed off surfaces and its use should be restricted to areas of low traffic. In addition the use of casein paint should be avoided in kitchens and bathrooms.
VOCs
The presence of VOCs in paint is significant both in terms of environmental impact and to health. Volatile Organic Compounds, VOCs, are organic compounds that have high enough vapour pressures to enable them to vaporise into the atmosphere. Organic solvents used in paint are a rich source of VOCs - White spirit, for example, contains the 'aromatic hydrocarbons' xylene, methyl benzene and ethyl benzene. Though solvents are the main source, VOCs are also emitted from other components such as some pigments (tints), fungicides and biocides - leading to a degree of variance amongst brands and colours of paint described as low-VOC.
VOCs are emitted both during application and for extended periods afterwards. One study demonstrated that less than 50% of the VOCs in latex paint are emitted in the first year. 10
The impact of paint on health
Paint, generally
• Though covering a less toxicity-aware era, a study published in 2002 and using data published in Sweden between 1960 and 1989, showed that incidences of cancers were 'significantly increased' for those employed in painting trades and paint manufacturing.1
• A study published in the journal 'Environmental Health Perspectives' in 2009 examined the possible association between the use of solvents and paint and child leukaemia. The study was inconclusive about links between solvents and leukaemia but it did find that there was a 'strong' link between the use of household paint and leukaemia:
'Because of the striking differences in the ORs for ALL risk between exposure to paint and to solvents, it is unlikely that the association observed with paint exposure is attributable to solvents contained in the paints. Household use of paint mainly involves latex paints, which typically contain vinyl acetate resin (polyvinyl acetate) or styrene-based resin (Kirk-Othmer 2006). Epidemiologic data and animal studies on polyvinyl acetate are too limited to allow evaluation of its potential carcinogenic risks in human beings… On the other hand, styrene has been classified as possibly carcinogenic to human, and several studies have reported increased risks of lymphatic and hematopoietic neoplasms in workers exposed to this product (IARC Monograph Working Group 2002), which makes styrene a putative candidate to explain the association between paint exposure and ALL risk.' 2
Solvents and VOCs
• A study in 2003 concluded that 'Domestic exposure to VOCs at levels below (then - ed) currently accepted recommendations may increase the risk of childhood asthma..' 3
• A review of recent research papers identified a number of studies that linked lung problems with painting 4
• The American Lung Association is widely reported '… 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.'
• Isoparaffins (see above) have a very low order of acute toxicity, being practically non-toxic by oral, dermal and inhalation routes. However, aspiration of liquid isoparaffins into the lungs during oral ingestion could result in severe pulmonary injury. 5
• Though temporary mental derangement through exposure to organic solvents has been understood since the nineteenth century, 'Organic Solvent Syndrome' refers to long-term neural toxicity resulting from prolonged exposure. Identified by an occupational health psychologist in Finland in the 1960s, its existence though largely accepted in Europe, is still debated in the UK. 6
• According to US Dept of Labor health guidelines, the 'natural' solvent gum turpentine is a skin, eye, mucous membrane and upper respiratory tract irritant. It may also cause skin sensitisation and central nervous system, gastrointestinal and urinary tract effects.
• Citrus oil (Limonene), another 'natural' solvent, is a skin and respiratory irritant. Thought once to be a cause of renal cancer in rats, there is no evidence for carcinogenicity in humans. 8
Additives
The impact of paint on the environment
The main environmental impacts associated with paint come from the manufacturer of the components, rather than manufacturing of the product itself.
Titanium Dioxide
By far the greatest environmental impact is derived from the manufacture of Titanium Dioxide (TiO2):
- High embodied energy (54 - 76 MJ/kg) 9
- Emissions during manufacture including (depending on process) CO2, N2O, SO2, NOx CH4 and VOCs 9
- A number of waste streams, including spent acid and metal sulfates, emanate from the manufacturing process, each of which carries an environmental impact. A number of EU directives seek to reduce and eliminate the pollution caused.
- Raw materials are derived from scarce resources
Coloured pigments
The environmental impacts associated with coloured pigments are various - though not as intense in their effects as those for Titanium Dioxide. It is worth noting too, that although there are 'natural' and 'man-made' pigments, not all 'natural' pigments have a lesser impact than man-made. Specifiers are recommended to examine closely the claims made by the manufacturer.
VOCs and Ozone
Ozone produced as part of human activities is a pollutant and a constituent of smog. Ozone is formed when nitrogen oxides, carbon monoxide and VOCs react in the atmosphere in the presence of sunlight.
Legislation and labels
Given the significant levels of VOCs traditionally associated with paints, it was not surprising that codes, labels and legislation have all been developed to limit their extent.
In terms of legislation, the EU VOC regulation is the most important and has the greatest impact on the issue. A number of codes and standards are also published, but without legislative backing, have relatively little traction.
VOC 2010 legislation
The Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations (aka VOC 2010 legislation) came into effect in 2010. The aim of the legislation has been to enforce cuts in VOC emissions on top of existing standards established in 2007.
The legislation breaks down paint function into 12 subcategories and assigns each category its own VOC limit. So for example 'Matt coatings for interior walls & ceilings' has water-based and solvent-based limits of 30 g/l whilst 'Interior/exterior trip & cladding paints for wood, metal & plastic' have limits of 130 g/l for water-based paint and 300 g/l for solvent-based paint.
Under BREEAM, 1 credit is available for products that meet with the legislation under the 'Health and Well-Being' category.
The EU Eco-label for indoor and outdoor paints and varnishes
The voluntary European eco-label sets the following standards:
• Limited Volatile Organic Content (VOC) and Volatile Aromatic Hydrocarbons (VHS)
• Reduced Sulphur emissions during production
• Reduced hazardous waste of by-products during titanium dioxide production
• No use of heavy metals and substances harmful for the environment and health
• User instructions for environmental use including storage conditions, waste
management and cleaning of tools
• Guarantee of minimum hiding power, wet scrub resistance, water resistance and
adhesion.
The standard sets out VOC limits according to a set of functional sub-categories. For example, 'Interior Matt' has a limit of 15 g/l (including water) and 'Interior trim and cladding paints for wood and metal including undercoats' has a limit of 90 g/l
Stringent limits are also placed on the emissions and discharges from the production of titanium dioxide pigment. Emissions include Sox as well as sulphate and chloride wastes.
To date, it is understood that only one manufacturer has attained the eco-label.
The paint industry has been typically forthright in its views of this very worthy standard, a spokesman from one leading manufacturer said in a letter that 'On the whole the paint industry does not intend to use this label'.
Environmental Protection Agency (USA) limits for VOCs
Low-VOC - less than 200 g /l
No-VOC - less than 5 g /l
Green Seal (USA) Standard GS-11 for Low VOC paint
This standard sets more stringent VOC-limitation standards than the US Government's own EPA. It is also is explicit about the components it prohibits - though many of them have already been dropped by manufacturers. The proscribed list includes:
• Halomethanes (methylene chloride)
• Chlorinated ethanes (1,1,1-trichloroethane)
• Aromatic solvents (benzene, toluene (methylbenzene), ethylbenzene)
• Chlorinated ethylenes (vinyl chloride)
• Polynuclear aromatics (naphthalene)
• Chlorobenzenes (1,2-dichlorobenzene)
• Phthalate esters (di (2-ethylhexyl) phthalate, butyl benzyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, diethyl phthalate, dimethyl phthalate)
• Miscellaneous semi-volatile organics (isophorone)
• Heavy metals and their compounds (antimony, cadmium, hexavalent chromium, lead, mercury)
• Preservatives (formaldehyde)
• Ketones (methyl ethyl ketone, methyl isobutyl ketone)
• Miscellaneous volatile organics (acrolein, acrylonitrile)
B & Q Paint labelling standard
Attributes 5 labels from 'Miminal' (0-0.29%) VOC content through to 'Very High' (more than 50%) based on g/ l of any organic compound having an initial boiling point less than or equat to 250oC measured at a standard pressure of 101.3 kPa.
Specifiying paint
Paint that fails is unsustainable
It should go without saying that paint should at least do the job - but the sad fact is that there are some paints, particularly amongst the 'eco' paints, on the market that just don't make the grade. Paint failures or inadequacies usually occur amongst outdoor paints. Common short-comings include:
• Paint of poor durability, including fading, poor adhesion, chalking, yellowing, colour fading - all requiring early re-coating.
• Low levels of coverage, necessitating several coats - increasing the overall environmental impact.
• Performance that falls short in only moderately demanding environments.
Greenwash
The paint industry is rich in Greenwash. The prefix 'Eco' works overtime and features on just about every tin of paint that has less VOCs than the industry average of 20 years ago. So common is the use of the word that it is now virtually, in paint terms, meaningless.
Those who have a belief in 'green' products will be saddened by the fact that nearly every manufacture, traditional or 'green', is guilty of misleading users about the levels of VOCs their paints contain. Particularly vexing is the oft-use of the expression 'Zero VOCs' when an analysis of the contents will, with few exceptions, reveal their presence - however much in small quantity.
Specifiers will be equally dismayed by misleading terminology. 'Natural' in particular is a word with a myriad of interpretations. 'Natural' doesn't always mean that a material has a low environmental impact or is non-toxic - for example, gum turpentine is often described as 'natural' but it is significantly toxic to people who use it. Linseed oil is 'natural' but uses a notable quantity of energy in its production.
As a fine example of a 'cloaking' expression, Neil May of Natural Building Technologies points to the almost homely use of the expression 'Vinegar ester' as an ingredient - which is another way of saying 'polyvinyl acetate' - a compound currently linked with cancer in rats, though no linkage has been demonstrated with cancer in humans.
Associating paint with familiar products in your kitchen cupboard - what are they thinking?
Specification
Specifying paint for low environmental impact and toxicity is not straightforward.
The greatest environmental impact will be from the manufacture of titanium oxide - a pigment so fundamental to the performance of any paint, that it is difficult to avoid - even amongst 'eco' paints. Alternatives exist, though careful consideration should be paid to embodied energy as well as performance - particularly coverage.
The most common toxic component of paint is from VOCs. Legislation is finally driving down levels, but many will consider that it still has some way to go. Other components such as additives are multifarious and difficult to recognise amongst other paint ingredients. Many additives are toxic, but there is very little legislative cover to accommodate all possible combinations. Standards have evolved both within and without the industry to try and control the more dangerous substances, but progress still needs to be made.
Great assistance could be provided by manufacturers if they would only volunteer to comprehensively list the ingredients of their paint.
The best guidance would be to:
• Specify water-based paint with low titanium oxide content together with low quantities of binder.
• Avoid paints with high levels of organic solvents - though this is becoming increasingly easy thanks to the effects legislation.
• Further reduce health concerns by careful study of lists of ingredients where available and the comparing of chemicals to databases of toxins.
• Where ingredients are not published, it might be fair to assume that there is a reluctance by the manufacturer to disclose - in which case it might be wise to avoid that product altogether,
References
1 Exposures in the Painting Trades and Paint Manufacturing Industry and Risk of Cancer Among Men and Women in Sweden - Brown, Linda et al, published in the Journal of Occupational and Environmental Medicine: March 2002
2 Household Exposure to Paint and Petroleum Solvents, Chromosomal Translocations, and the Risk of Childhood Leukemia - Scélo, Metayer et al, Univ California, 2009
3 Association of domestic exposure to volatile organic compounds with asthma in young children - Rumchev et al, Curtin University of Technology, Perth
4 Indoor Residential Chemical Emissions as Risk Factors for Respiratory and Allergic Effects in Children: a Review - Mark J. Mendell, Lawrence Berkeley National Laboratory, published in Indoor Air Journal, 2007
5 Toxicology update isoparaffinic hydrocarbons: A summary of physical properties, toxicity studies and human exposure data - Mullin, Ader et al, published in the Journal of Applied Toxicology , April 1990
6 Watching paint dry - Dr Anne Spurgeon, Univ of Birmingham, 2006
7 Cobalt and antimony: genotoxicity and carcinogenicity - De Boeck, Kirsch-Volders and Lison - Vrije Universiteit Brussel & Université catholique de Louvain, 2003
8 IARC Monographs on the evaluation of carcinogenic risks to humans 1999, 73-16, 307-27
9 Environmental Impact of Coated Exterior Wooden Cladding - Hakkinen et al, VTT Building Technology, 1999
10 Volatile Organic Compound Emissions from Latex Paint - Part 2. Test House Studies and Indoor Air Quality (IAQ) Modeling - Sparks et al, 1999 published in Indoor Air, the international journal of indoor environment and health
Further information
• Toxin and Toxin Target Database (T3DB) - This excellent database contains 2900 toxins - http://t3db.org
Paint products on GreenSpec
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