Building Materials, Third Edition

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are used to hide the surface imperfections and to impart the desired colour. They
protect the paint film by reflecting the destructive ultra violet light, which acts as a catalytic
agent for the destructive oxidation of the film. They also improve the impermeability of the
paint film and enhance its resistance to weathering, affect the flow characteristics making it
possible to paint vertical and uneven surfaces smoothly. Pigments are finely ground mineral,
organic substances or metal powders; their size in organic coatings ranges from 0.1 to 5.0
microns in diameter. Their general properties are covering power, colouring capacity, fineness,
fire resistance, chemical stability and weather resistance. The fine particles of the pigments
have a reinforcing effect on the paint film.
The common pigments are classified as natural and artificial. The former used for preparing
limestone and glue paints, putties and coloured building mortars, include ground natural
white chalk, mastics, grey graphite, dry yellow ochre (a clay containing over15 per cent of iron
oxide), etc. Artificial mineral pigments, obtained by chemical processing of raw mineral
materials, include titanium dioxide, zinc white, lead white (2 PbCO 3 .Pb (OH) 2 ), lithophone
(BaSO 4 + ZnS), chrome oxide, red lead, gas black soot, etc. metal powders such as aluminium
powder, metallic powders, gold dust, etc. synthetic substances of organic origin, possessing
high dyeing capacity. Some of the examples of pigments used to produce the desired colours
are lamp black and ivory black (Black), Prussian blue, indigo (Blue), chrome yellow, yellow
orchre (yellow), burnt umber, burnt siena (Brown), vermilion, red lead (Red) and copper
sulphate (Green).

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are the oils used to thin the paints, increase the spread, and are also known as
thinners. They make the paint of workable consistency and evaporate during drying of the
film. The common thinning agents used are petroleum, spirit, naptha and turpentine oil—a

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