Paints, wood stains, varnishes and colour

Colour being a key feature of architectural design is an important factor in the description of paints, wood stains and varnishes.

The Natural Color System®© (NCS) was developed by the Scandinavian Colour Institute in the 1980s and modified in 1995 with a second edition in which extra colours were added and some removed leaving a total of 1950 colours. It is a colour language system which can describe any colour by a notation, communicable in words without the need for visual matching. It has been used by architects, builders and designers who need to coordinate colour specification across a broad range of building products. A range of materials can be colour-referenced using the system; these include wall, floor and ceiling tiles, carpets, fabrics, wall coverings, flexible floor finishes, paints, architectural ironmongery and metalwork, sanitary fittings, laminates and furniture.

The Natural Color System®© is based on the assumption that for people with normal vision there are six pure colours; yellow, red, blue, green, white and black. The four colours, yellow, red, blue and green are arranged around the colour circle, which is then subdivided into 10% steps. For example, yellow changes to red through orange, which could be described as Y50R (yellow with 50% red) (Fig. 7.2).

Paints consist of a blend of components, each with their specific function. Commonly, these include the binder (or medium), solvent, base, extenders, pigments and driers, although other additives may be incorporated into specialist paints.

The binder is solidified to produce the paint film. Traditionally, the binder was natural linseed oil, which set by gradual oxidation on exposure to air. However, linseed oil has now largely been replaced by alkyd resins which oxidise in air, or vinyl and acrylic resins which solidify by drying. To ensure adequate fluidity of the paint during application by brushing or spraying, either water or organic solvents (hydrocarbons, ketones or esters) are incorporated; paint thinners have the same effect. The base material, usually white titanium dioxide, produces the required opacity, although the body of the paint may be increased by the incorporation of inert extenders such as silica, calcium carbonate, china clay or barytes. Colouring materials are frequently a mixture of organic and inorganic dyes and pigments. Driers which induce the polymerization of the binder ensure a rapid drying process.

Natural wood finishes include wood stains, varnishes and oils. Wood stains are pigmented resin solutions which penetrate into the surface and may then build up a sheen finish. Varnishes are unpigmented resin solutions which are intended to create a surface film.

Most wood stain systems for exterior use include a water- or solvent-based preservative basecoat which controls rot and mould growth. Typical formulations include zinc or copper naphthenate, dichlorofluanid, tri-(hexylene glycol) biborate and disodium octaborate tetrahydrate. Wood stain finishes are either low-, medium- or high-build systems, according to the particular application. They usually contain iron oxide pigments to absorb the ultraviolet light which otherwise causes the surface degradation of unprotected timber. Generally, for rough-sawn timber, deeply penetrating wood stains are appropriate, whereas for smooth-planed timber a medium or high - build system gives the best protection from weathering. Products are based on acrylic and/or alkyd resins.

Traditional varnishes are combinations of resins and drying oils, but most products are now based on modified alkyd resins. Polyurethane varnishes are available in matt, satin or gloss finishes, based on either water or solvent-based systems.

Wood finishes entirely composed of natural products are also available. These are based on blends of beeswax, larch resin, vegetable oils, and may incorporate minerals and earth pigments for colour and opacity.