Pre-reading Discussion. 1. What is the main function of colour in architecture?

1. What is the main function of colour in architecture?

2. Do you agree that colour is used in building only for its tonal quality?

3. How can colour affect the general view of a building?

4. What colour tones do you prefer?

5. What does paint consist of?

The encyclopaedist Isidor of Seville (560-636) described colour as "captive sunlight", while Sir Isaac Newton

attempted to fit the colours of the rainbow into a linear, measurable spectrum, and Johann Wolfgang von

Goethe developed a non-scientific colour circle as part of his theory of colour. According to a definition in

modern German standards, "Colour is the facial sensation of part of the field of vision that appears unstructured

to the eye, by means of which that part - observed with a single, unmoving eye – can be solely differentiated

from a similarly unstructured adjoining area seen at the same time."

Colour is used in buildings not only for its tonal quality, but also as part of the actual construction - in the

form of finishings that provide protection against the weather. In this context, it is perhaps more useful to speak

of " coatings ", a term that covers a wide range of protective products from fluid, paste-like or even powdered

materials to conventional paints. Painted finishes are usually built up in a number of layers, which together

form a system of priming coats, undercoats and finishing coats. Sometimes the surface to be painted may also

be otherwise treated to improve adhesion. As with plasterwork, the finishing coats should be softer than the undercoats

to avoid cracking caused by tension between the layers. Generally speaking, the application of a few

thick coats of paint is less elaborate than a greater number of thin coats, but the latter technique ensures a better

drying-out process and produces a smoother, more even finish. The choice of material will depend on the vapour-

diffusing properties and permeability of the individual layers or coats, which should be matched to the

base and take account of weather conditions.

Painted coatings can be classified according to various criteria: their special protective qualities (against

fire or corrosion, for example); the construction elements on which they are used (windows, facades, etc.); or

the material to which they are applied (wood, steel, mineral backings, etc.). The most logical and universal classification,

however, is according to the binding agent used; e.g. alkyd resin; or silicate paints based on the use

of potassium silicate. The painting system and the background material have a reciprocal influence on each

other and determine the properties of the finished construction in terms of impermeability, vapour diffusion and

strength.

Paint, as a liquid surface coating, consists of binders, solvents, fillers, pigments and additives, which together

determine the properties of a product and its coloration. Up to the middle of the 20th century, paints

were mixed by the trade people who used them. Today, most paints come as finished products ready mixed by

the manufacturers. This ensures constant, controllable quality standards, but the subtle variations in tone and the

liveliness of traditionally mixed paints have disappeared. Binders belong to the non-volatile components of

paint and are important for the adhesion of the material on various backgrounds. Solvents serve to dissolve the

binders and make them workable. Pigments determine the colour and may be of inorganic, mineral or organic

origin. Additives can also be incorporated to improve the storage life, workability, visual quality, etc.

The first paints used by man were made of earth. The cave dwellers used red ochre or black

manganese earth, with added charcoal and red chalk, more than 15,000 years before Christ. Later, lime milk

was employed for whitewashing plaster or stone. Over the millennia, paints underwent a constant process of

improvement in respect of their adhesion and brushability through the addition of natural substances like curd

and linseed oil. For lime-based paints, slaked white lime diluted with water Ca(OH)2 is used as a binder. Since

lime-based paints require constant maintenance, however, their use externally is restricted mainly to historical

buildings where it is necessary to match new with existing materials. In external situations, there is also a danger

that the lime content will be converted into gypsum as a result of acid rain. Internally, on the other hand,

lime-based paints are used today for their good vapour-diffusing and absorbent properties and their ability to

regulate moisture levels. In addition, they are greatly appreciated for the tonal radiance they help to achieve.

Distempers and casein paints, which are mainly suitable for internal use, no longer play an important role

nowadays, except in biologically correct forms of construction.

Today, the wide range of paint products on the market has made it necessary to establish certain criteria for

the selection of the appropriate type for a specific situation. A new system of classification for facade paints is

at present being drawn up and is scheduled to be completed next year. This is based on the so-called S-value

(the depth of an air-layer with the equivalent rate of diffusion) and the W-value (the degree of water repellence),

which form the measure of comparison. This new code of classification will allow the selection of paints

that are precisely matched to a particular backing.

In order to determine the moisture balance of a component, a distinction must be made between paints that

form a film on drying and those that do not. In conjunction with the binding agent used, additives can be

incorporated in dispersion substances to control the formation of a surface film and thus to regulate the

permeability or moisture resistance of the coating, if no film is formed, water glass can penetrate mineral paints

and cause a reaction in the bearing layer (silification). These processes have a great influence on the industrial

manufacture of paints today and result in a division of products into dispersion paints on the one hand, and

silicate or mineral-based paints on the other.

Potassium silicate is a syrupy fluid created through the fusion of quartz with potash or soda. It is used as a

fixative or binder for silicate paints. Their development dates back to the late 19th century. Pure silicate paints

are two-component products consisting of a fixative and coloured powder (mineral pigments with fillers). The

materials have to be soaked or mixed a day before use. When the paint dries, the water glass does not form a

sealed film; instead, a process of petrification or silification occurs in the mineral base. The open-pore structure

ensures a high degree of permeability to vapour and allows a rapid drying process. The surface finish is also

highly resistant to pollutants and aggressive substances. That is why silicate paints are frequently used in place

of historical lime-based paints in conservation. In such situations, the strength of the rendering should be coordinated

with the surface finish. Because the mineral binding agent has the same coefficient of expansion as

the mineral base, stresses caused by changes of temperature - and the resulting cracking - can be avoided. Since

their development at the beginning of the 20th century, water-based (dispersion) paints have come to play a major

role in view of their simple preparation and broad range of application. The binding agent consists of polymerisation

resins dispersed in water, to which softeners, fillers and pigments are added as required. In chemical

terms, mixes in which the substances are not dissolved but merely finely distributed in the solvent are

known as "dispersions". Where the finely distributed matter is a solid, one speaks of a "suspension"; where it is

a fluid, it is referred to as an "emulsion". These paints are suited to both internal and external use. The way they

set depends on the nature of the suspension or emulsion substance they contain as well as on the drying-out

process. At all events, a continuous film is formed. As an organic system, the paint does not bond with the mineral

background; it simply adheres to the surface. Additives can be used to modify the properties of the film to

ensure adequate vapour diffusion without affecting the great weather resistance it possesses. Since the waterabsorbing

and vapour-diffusing properties of paints can be determined in the manufacturing process, planners

are confronted with something of a dilemma. Dispersions are easy to work and strongly resistant to moisture. In

addition, as described above, they form a surface-sealing film. Silicate-based paints, on the other hand, form an

open-pore, mineral-based finish and absorb more moisture. Industry has, therefore, modified the manufacturing

processes to combine some of the positive properties of both products.

Single-component silicate dispersion paints may contain a maximum of 5 per cent organic material. They

adhere to all mineral backgrounds and combine the advantage of silicate paints (high permeability to moisture)

with the low water-absorption property of dispersions. Additives can also be used with these products to improve

durability and adhesion, and to ensure uniform coloration during the drying process. The low dispersion

content means that no surface film is formed, but the amount of water absorption is reduced without negatively

affecting the vapour-diffusing quality.

Silicone-resin paints consist of synthetic (mostly acrylate) dispersions, pigments, fillers and silicone-resin

emulsions. These products are increasingly taking the place of dispersions, since they eliminate the disadvantages

of purely silicate-based systems. As with dispersion systems, when the synthetic dispersion content is low

(about 5 per cent), the water repellence of the paint will be high (low W-value), yet it will possess good vapour

diffusing properties (low S-value). The dispersion content is nevertheless necessary to reduce the degree of

chalking and to ensure surface resistance to abrasion.

Regardless of the different compositions of paints, all coatings can be compared in their perceptible colour

tones, and various colour systems have been developed for this purpose. In the absence of recognised international

standards, many countries have their own coding systems. In Germany, the most commonly used is the

PAL colour tone register. Paints for rendering and facades are sometimes classified according to the Scandinavian

"natural colour system" (NCS), which is based on six basic colours: black, white, blue, red, yellow and

green. More spatial definition is provided by colour codes based on the C/E system. In this case, the classification

is derived from sensory physiological measurements translated into mathematical models.

Despite all these attempts at classification, however, the effect of coating systems is strongly dependent on

the perception of the observer, the materials used and the lighting conditions, so that even today it is still possible

to observe "captive sunlight" on facades.