Important archive and safety note: This text preserves historical classifications, procedures and claims from the source article. It is not a current coating specification, selection recommendation or work instruction. Product composition, substrate compatibility, emissions, toxicity, flammability, fire performance, personal protective equipment, ventilation, application and disposal must be checked against the current technical data sheet, safety data sheet and manufacturer’s documentation. Particular care is required with solvents, spray application, lead- and chromate-based pigments and old coatings.
Historical products and claims mentioned in the text are not presented as materials currently used by Savo Kusić. For the current context, see painting and varnishing and the RAL colour chart.
Basic classification
These are substances that, when applied to surfaces, leave a thin decorative or protective layer (or both). What is required from these agents is: good plasticity, which allows obtaining a uniform coating, perfect adhesion to the substrate, reasonable service life and color fastness. We classify coloring agents according to the substances that make them up.
Water-based paints
Water-based paints use water as a solvent. They are easy to apply and dry quickly (about 2 hours). The source article specifically associates them with painting mortar and concrete.
Limewash, obtained by diluting slaked lime, is used for inexpensive painting, but is not resistant: even light rubbing makes it crumble. Lime paints adhere well to mortar, but not to gypsum or putty, and the source article says that they are rarely used because of their short service life or poor adhesion to the substrate. They can be made somewhat more stable with certain hardeners, while other water-soluble colours can be added to obtain a range of shades.
Gypsum- and glue-based paints are not highly resistant to wiping and are used only indoors. The article describes preparing them from a special gypsum powder mixed and dissolved in water, then bound with glue. Cellulose glue in flakes was said to be the most widely used because of its practicality. After brief soaking in water, it forms a more or less thick paste. Different shades can readily be obtained with water-based vinyl colours. Gypsum- and glue-based paint cannot be applied over old layers. Before repainting, an old layer on a gypsum substrate must be removed with a damp sponge until bare gypsum is reached; on a mortar substrate, it must likewise be scraped while wet.
Distemper or non-washable water-based paints form a relatively resistant film as they dry, but the film comes off when it contacts water. The article says that these paints were formerly bound by heating them with a special glue, whereas ready-made products later became common. An old distemper layer can be recoated at least once, but must be scraped off if the mortar substrate needs to be exposed. The source describes washable water-based paints as the most dependable products in this group. They can be applied to many materials, including different types of mortar and wood, and are available in a broad range of colours. Although they readily form a layer resistant to water and rubbing, the article says that they do not allow walls to “breathe”. A new coat can be applied over old paint after simply washing the surface. The paints described use titanium white as the principal pigment and synthetic resins as the binder. Indoor and exterior water-based paints differ somewhat in binder quality—vinyl and acrylic respectively—and in pigments, described in the first case as brighter and in the second as exceptionally light-resistant. Exterior water-based paints may also be used indoors, but not the reverse.
Lacquers
Lacquers use different substances as solvents, which evaporate faster or slower. They are used mainly to cover wooden or metal surfaces, on which they form a very resistant layer, impermeable to water. Clear varnishes are those that, when applied to a surface, allow the substrate to be seen. Pigmented varnishes, on the other hand, leave a colored film. Enamel is a special kind of varnish that gives a shiny surface layer.
Several categories of varnish are distinguished according to their components. Oil-based varnishes are described as being based on volatile oils—most often boiled linseed oil—and natural resins. They use turpentine as a solvent and take at least six hours to dry. Clear varnishes of this type are mainly used to coat and protect wood while leaving its characteristic grain and fibres visible. Pigments in opaque coloured varnishes include zinc white and titanium white, with special oil colours added to obtain a wider range of shades. Besides coating wood and iron or other metals, the article says that these varnishes were often applied to create impermeable surfaces on exterior and interior walls. Synthetic varnishes are made from synthetic resins, with or without natural oils dissolved in suitable solvents. Both clear varnishes and enamels have the same applications as oil-based varnishes, but are described as more resistant to moisture and weathering and as drying more quickly (about three hours).
Alcohol-based varnishes are solutions of special resins, of the copal type, in alcohol. The source says that both clear varnishes and enamels of this kind are used only as an undercoat rather than a finishing coat because they produce mediocre results.
Nitrocellulose varnishes contain, in addition to special solvents, natural and artificial plasticizing substances and resins. Their main characteristic is that they evaporate (dry) in the shortest possible time (in about 30 minutes) and that they form an extremely thin layer. For this reason, they are most often applied by spraying rather than by brushing (they are sold in spray bottles). They are widely used to paint metal, and give good results on wood and the most common wall substrates.
Water-based enamels simplify small lacquer work because they do not require any prior preparation with base colors (base colors). And the fact that they do not require special solvents, but can be dissolved with ordinary water, is not a small advantage. In terms of resistance, gloss and durability, they are no worse than traditional enamels.
Protective paints and varnishes
Protective paints and varnishes are intended to protect the surfaces to which they are applied and preserve the material. The source article states that an appropriate product exists for almost every preservation problem.
Waterproof varnishes, such as those based on silicone, are transparent liquids that protect surfaces from moisture and do not change their appearance. They are often applied to external walls as well.
Lacquers based on polyester and polyurethane form a protective transparent layer on the wood that is impermeable to water and quite resistant to scratches. They are used for wooden floors and window frames, doors and in general, exterior woodwork.
The source article claims that antibacterial, antiparasitic and fungicidal paints protect not only wood but also other materials—mortar, concrete, stone and brick—from organisms, and that they are non-toxic and cannot be washed away by rain. These historical claims require verification against the current product documentation noted above.
Anti-saltpetre paints are applied with a brush to walls damaged by saltpetre. We should first clean the walls well with a brush. They serve as a basis for painting, wallpapering or other wall coverings.
Finally, the article describes fire-retardant paints intended to protect wood and other combustible materials from fire. It claims that such paints can prevent a larger fire following a short circuit or a discarded cigarette. The described product is applied to wood, cardboard, plywood or hardboard in a layer about one tenth of a millimetre thick. On contact with fire, it is said to form a firm foam that separates the flame from the coated material. Another type of fire-protective wood coating is described as preventing charring and preserving the mechanical properties of the wood. These claims must not be used as a fire-safety specification without current tested documentation.
Products for substrate preparation
Substrate preparations are paints that are applied with a brush as the first coat on surfaces to better receive the following, final “coats”. They can be:
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insulating paints, which equalize the porosity of the substrate (mortar, wood) and prevent stains caused by uneven absorption from appearing in the finished coating;
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wood primers, such as cementite and similar products, which fill the pores of the wood and create a smooth surface for subsequent varnishing;
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anticorrosive paints applied to metal to prevent rust.
The historical text mentions classic red lead (lead oxide) in linseed oil, as well as synthetic products with chromium- and iron-oxide-based pigments, which are described as drying much faster. It also mentions products that dry faster still—in one hour on average—and says that wash primers improve varnish adhesion to metal and are necessary as a first coat on galvanized metal that would not otherwise accept ordinary varnish. Current legal, health, environmental and product requirements take precedence over this archival description.