Building Materials, Third Edition

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Varnishes provide a protected coating and gloss to the surface and intensify the wood
grains.

The objects of varnishing a surface are to:

1. Brighten the appearance of the grain in wood.


2. Render brilliancy to the painted surface.


3. Protect painted surface from atmospheric actions.

Characteristics of an ideal varnish:

1. It should render the surface glossy.


2. It should dry rapidly and present a finished surface which is uniform in nature and
   pleasing in appearance.


3. The colour of varnish should not fade away when the surface is exposed to atmospheric
   actions.


4. The protecting film developed by varnish should be tough, hard and durable.


5. It should not shrink or show cracks after drying.

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Varnish is applied as under:

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22ƒ—™ The wood work is made smooth by rubbing it with sand paper and
the surface is cleaned.

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 is the process of covering the knots in the wood work, using any of the following
methods.

ƒ2 
 A coat of red lead ground in water mixed with glue size is applied. After it
dries another coat of red lead ground in oil and thinned by boiled turpentine oil is applied.

€—2 
 Two coats of varnish prepared by dissolving shellac in methylated sprit or
wine, are used.

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 The surface of the wood work is then rubbed again and cleaned. Before rubbing,
the surface is applied with size of hot, weak glue.

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2™— Varnish is then applied in two coats. The second coat is applied after the first
has dried.

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Varnishes are classified as oil, spar, flat, spirit and asphalt varnishes.