It all started in the mid nineteenth century, with LudvigI, King of Bavaria. Even as a young prince, Ludvig wascommitted to the spirit of classicism and humanismand was an enthusiastic and active patron of both thearts and building design. In Italy, the art-loving Ludvigwas in his element and so struck by the colourful limefrescoes that he was inspired to create similar works ofart in his own country. However due to the harshwinter climate north of the Alps, his attempts failedand he subsequently commissioned his Bavarianscientists to create a paint that looked and behaved likelimewash, but was also significantly more durable andlong lasting.

Luckily for Ludvig, they achieved his goal, by usingpotassium silicate, one of the waterglasses.

Like limewash, silicate paints work by soaking into theunderlying material and in addition, the potassium

silicate reacts chemically with it to form an insolublemicrocrystalline bond; a process known as silicification.This process helps ensure that the coating will noteasily peel, chip or flake off, as would happen withmany modern acrylic paints. When silicate paints areapplied they allow the free passage of moisture vapourfrom the underlying material, allowing the substrate tobreathe, whilst the small pore structure also helpsreduce the ingress of further moisture. Breathability isessential in historic buildings, traditional buildings withsolid wall construction, and also many contemporarysustainable buildings, which may contain moisturefrom a range of sources.

Silicate paints are suitable for all mineral surfaces, limerenders, cement renders, concrete and bare stone,making them ideal for internal and external walls, andcan also be used inside on areas where limewash or

The Silicate SolutionPaints with benefits by Tanya Jewell

Above, South Devon Cottages with SecilTEK silicate paint

Conservation & Heritage Journal8

ii

final issue 8:Layout 1 7/20/15 10:43 AM Page 8

Conservation & Heritage Journal9

ii

emulsion might not work , for instance on dampinternal stone walls or basements. Silicate paints canprovide necessary protection and extreme durabilitywith little or no impact on the environment.

As well as being very durable, silicate paints are highlybreathable, unaffected by ultraviolet light and resistantto both acid rain and mould-growth. Unlike modernacrylic paints, silicate paints are non-combustible andwill not contribute to the spread of fire or smokedevelopment. Acrylic paints by contrast give off highlytoxic smoke and increase the spread and intensity ofany fire. For this reason, when used in the restorationof historic buildings, it is possible that insurancepremiums can be significantly reduced. In regionswhere fire is a threat such as earthquake zones, sodiumsilicate, another type of waterglass, is sprayed onto thebuildings as a cheap method of fireproofing them.

Silicate paints fall into one of three categories – puresilicate, silicate dispersion and sol-silicate paints.

Today the majority of commercially available silicatepaints are silicate dispersion paints. These have manyadvantages over limewash and film-forming modernacrylic paints, such as -

● A minute pore size allowing high vapour permeability, yet not allowing rain penetration, as thewater molecules are too large

● Entirely unaffected by UV light (which can causemodern acrylic paints to become brittle and split overtime) thereby retaining their original colour

● Water repellent and resistant to airborne pollutants,particularly acid rain

● Very durable with a long life (with known examplesfully protected and still going strong after manydecades), making it a very cost effective choice andideal for projects where minimal maintenance isrequired

● Suitable for all mineral surfaces, internal andexternal, including lime renders and plasters, cement,stone, brick, gypsum

● A comparable thermal expansion co-efficient to themineral substrate thereby reducing stresses andminimising differential expansion (a big problem withmany modern acrylic paints)

● The solvent is water (in many modern acrylic paintsthe solvent is petrochemical)

● Passive fire resistance, particularly suitable for highlypopulated buildings, public and communal areas

● Minimal attraction for dust and dirt, and alsoscrubbable, therefore ideal for high traffic areas

To be clear, modern acrylic paints form a covering tothe substrate through mechanical adhesion. They forma film which prevents the fabric from breathing,resulting in trapped moisture and cryptoflorescence,where salts are deposited within the fabric of thebuilding. The consequence of this is that the paint candelaminate from the substrate resulting in extensivedamage not only to the building fabric, but also tostructural timbers and internal finishes. In comparisonsilicate paints chemically bond to the substrate, andhave a high vapour permeability rate which allows thebuilding to breathe. This prevents the build up ofmoisture and therefore the coating will not crack orpeel.

A one-time application of a silicate paint can providea durable, protective and breathable surface lasting fordecades, which can be washed as necessary without anydamage to the surface or substrate. With modernacrylic paints, mould and fungi can form in areas oftrapped moisture, and where moisture runs down theinside of walls, which can attack internal timbers andfinishes.

Silicate paints, being derived from mineral rawmaterials, are environmentally friendly in bothproduction and in use, with the long life of the productsaving on costs and natural resources, helping toprotect the environment and our health, as well as ourbuildings.

Silicate Paints – The three types )Pure Silicate Paints : for only very pure mineralsubstrates and comprising two components - the binder(waterglass) and the powder (pigment and fillers)- which must be combined immediately prior toapplication. This is a process that requires significantskill and knowledge and is now used almost exclusivelyby historians.

Silicate Dispersion Paints : come ready prepared andcontain a small quantity of acrylic binder, suitable for amuch wider range of substrates including those of lowerstrength. The manufacturing process is much simplerthan for Pure Silicate Paints.

Sol-silicate Paints : comprising silica sol and waterglass;specifically designed to cover previously paintedsurfaces such as acrylics and glosses, and on non-mineral plasters. The binding is both chemical andphysical.

final issue 8:Layout 1 7/20/15 10:43 AM Page 9

Conservation & Heritage Journal10

ii

Silicates - What are they? 'Silicon is a chemical element, one of the 97 naturalbuilding blocks from which our minerals are formed.A chemical element is a substance that can't besubdivided into simple substances without splittingatoms. Silicon is the second most abundant elementon the earth's crust, making up about 27% of theaverage rock. Silicon links up with oxygen (whichmakes up 55% of the earth's crust) to form the mostcommon suite of minerals, called the silicates. Quartz,feldspars, olivine, micas, thomsonite, jadeite, andprehnite are all silicates. There is so much oxygen aroundthat pure native silicon is almost never found naturally.Silica is a bit of a trickier concept. It refers to thecombination of silicon plus oxygen. The mineral quartzis silica, but so are the minerals tridymite, coesite,cristobalite and stishovite which are mineral forms ofsilica that are stable at high temperature and pressures.All these minerals are also silicates. In other wordsquartz is a silicate made out of pure silica. But feldsparscontain sodium, aluminium, potassium and calcium inaddition to silicon and oxygen. Thus feldspars aresilicates but they are not pure silica.' ■

Dr Bill Cordua

References/Further readingCordua, B. (1998) Silicon, Silica, Silicates and Silicone, University of WisconsinDavies, G. (1996) Vapour Permeable Paint, The Building Conservation DirectoryParker, J. (2003) Inorganic Coatings for Restoration, Masonry MagazineTesh, G, (2009) A Natural Solution to Painting and Decorating, Sustain Magazine

Above, South Devon Cottage with SewcilTEK silicate paints

Tesh, G. (2002) Paints and their History, The WesternMorning Newswww.jackinthegreenlime.co.uk/silicate.htmlwww.memim.com/silicate-mineral-paint.htmlTanya Jewell is a Technical Sales Adviser for Mike Wye andAssociates Ltd., specialising in Natural Paints and finishes.www.mikewye.co.uk

final issue 8:Layout 1 7/20/15 10:43 AM Page 10