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The Silicate Solution
Paints with benefits by Tanya Jewell
It all started in the mid nineteenth century, with Ludvig
I, King of Bavaria. Even as a young prince, Ludvig was
committed to the spirit of classicism and humanism
and was an enthusiastic and active patron of both the
arts and building design. In Italy, the art-loving Ludvig
was in his element and so struck by the colourful lime
frescoes that he was inspired to create similar works of
art in his own country. However due to the harsh
winter climate north of the Alps, his attempts failed
and he subsequently commissioned his Bavarian
scientists to create a paint that looked and behaved like
limewash, but was also significantly more durable and
long lasting.
silicate reacts chemically with it to form an insoluble
microcrystalline bond; a process known as silicification.
This process helps ensure that the coating will not
easily peel, chip or flake off, as would happen with
many modern acrylic paints. When silicate paints are
applied they allow the free passage of moisture vapour
from the underlying material, allowing the substrate to
breathe, whilst the small pore structure also helps
reduce the ingress of further moisture. Breathability is
essential in historic buildings, traditional buildings with
solid wall construction, and also many contemporary
sustainable buildings, which may contain moisture
from a range of sources.
Luckily for Ludvig, they achieved his goal, by using
potassium silicate, one of the waterglasses.
Silicate paints are suitable for all mineral surfaces, lime
renders, cement renders, concrete and bare stone,
making them ideal for internal and external walls, and
can also be used inside on areas where limewash or
Like limewash, silicate paints work by soaking into the
underlying material and in addition, the potassium
Above, South Devon Cottages with SecilTEK silicate paint
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emulsion might not work , for instance on damp
internal stone walls or basements. Silicate paints can
provide necessary protection and extreme durability
with little or no impact on the environment.
● Minimal attraction for dust and dirt, and also
scrubbable, therefore ideal for high traffic areas
To be clear, modern acrylic paints form a covering to
the substrate through mechanical adhesion. They form
a film which prevents the fabric from breathing,
resulting in trapped moisture and cryptoflorescence,
where salts are deposited within the fabric of the
building. The consequence of this is that the paint can
delaminate from the substrate resulting in extensive
damage not only to the building fabric, but also to
structural timbers and internal finishes. In comparison
silicate paints chemically bond to the substrate, and
have a high vapour permeability rate which allows the
building to breathe. This prevents the build up of
moisture and therefore the coating will not crack or
peel.
As well as being very durable, silicate paints are highly
breathable, unaffected by ultraviolet light and resistant
to both acid rain and mould-growth. Unlike modern
acrylic paints, silicate paints are non-combustible and
will not contribute to the spread of fire or smoke
development. Acrylic paints by contrast give off highly
toxic smoke and increase the spread and intensity of
any fire. For this reason, when used in the restoration
of historic buildings, it is possible that insurance
premiums can be significantly reduced. In regions
where fire is a threat such as earthquake zones, sodium
silicate, another type of waterglass, is sprayed onto the
buildings as a cheap method of fireproofing them.
A one-time application of a silicate paint can provide
a durable, protective and breathable surface lasting for
decades, which can be washed as necessary without any
damage to the surface or substrate. With modern
acrylic paints, mould and fungi can form in areas of
trapped moisture, and where moisture runs down the
inside of walls, which can attack internal timbers and
finishes.
Silicate paints fall into one of three categories – pure
silicate, silicate dispersion and sol-silicate paints.
Today the majority of commercially available silicate
paints are silicate dispersion paints. These have many
advantages over limewash and film-forming modern
acrylic paints, such as ● A minute pore size allowing high vapour
permeability, yet not allowing rain penetration, as the
water molecules are too large
Silicate paints, being derived from mineral raw
materials, are environmentally friendly in both
production and in use, with the long life of the product
saving on costs and natural resources, helping to
protect the environment and our health, as well as our
buildings.
● Entirely unaffected by UV light (which can cause
modern acrylic paints to become brittle and split over
time) thereby retaining their original colour
● Water repellent and resistant to airborne pollutants,
particularly acid rain
Silicate Paints – The three types )
Pure Silicate Paints : for only very pure mineral
substrates and comprising two components - the binder
(waterglass) and the powder (pigment and fillers)
- which must be combined immediately prior to
application. This is a process that requires significant
skill and knowledge and is now used almost exclusively
by historians.
● Very durable with a long life (with known examples
fully protected and still going strong after many
decades), making it a very cost effective choice and
ideal for projects where minimal maintenance is
required
● Suitable for all mineral surfaces, internal and
external, including lime renders and plasters, cement,
stone, brick, gypsum
Silicate Dispersion Paints : come ready prepared and
contain a small quantity of acrylic binder, suitable for a
much wider range of substrates including those of lower
strength. The manufacturing process is much simpler
than for Pure Silicate Paints.
● A comparable thermal expansion co-efficient to the
mineral substrate thereby reducing stresses and
minimising differential expansion (a big problem with
many modern acrylic paints)
Sol-silicate Paints : comprising silica sol and waterglass;
specifically designed to cover previously painted
surfaces such as acrylics and glosses, and on nonmineral plasters. The binding is both chemical and
physical.
● The solvent is water (in many modern acrylic paints
the solvent is petrochemical)
● Passive fire resistance, particularly suitable for highly
populated buildings, public and communal areas
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Silicates - What are they?
'Silicon is a chemical element, one of the 97 natural
building blocks from which our minerals are formed.
A chemical element is a substance that can't be
subdivided into simple substances without splitting
atoms. Silicon is the second most abundant element
on the earth's crust, making up about 27% of the
average rock. Silicon links up with oxygen (which
makes up 55% of the earth's crust) to form the most
common suite of minerals, called the silicates. Quartz,
feldspars, olivine, micas, thomsonite, jadeite, and
prehnite are all silicates. There is so much oxygen around
that pure native silicon is almost never found naturally.
Silica is a bit of a trickier concept. It refers to the
combination of silicon plus oxygen. The mineral quartz
is silica, but so are the minerals tridymite, coesite,
cristobalite and stishovite which are mineral forms of
silica that are stable at high temperature and pressures.
All these minerals are also silicates. In other words
quartz is a silicate made out of pure silica. But feldspars
contain sodium, aluminium, potassium and calcium in
addition to silicon and oxygen. Thus feldspars are
silicates but they are not pure silica.' ■
Dr Bill Cordua
References/Further reading
Tesh, G. (2002) Paints and their History, The Western
Morning News
www.jackinthegreenlime.co.uk/silicate.html
www.memim.com/silicate-mineral-paint.html
Tanya Jewell is a Technical Sales Adviser for Mike Wye and
Associates Ltd., specialising in Natural Paints and finishes.
www.mikewye.co.uk
Cordua, B. (1998) Silicon, Silica, Silicates and Silicone,
University of Wisconsin
Davies, G. (1996) Vapour Permeable Paint,
The Building Conservation Directory
Parker, J. (2003) Inorganic Coatings for Restoration,
Masonry Magazine
Tesh, G, (2009) A Natural Solution to Painting and
Decorating, Sustain Magazine
Above, South Devon Cottage with SewcilTEK silicate paints
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