Exterior Decorating: Varnishing Exterior Woodwork

Grained woodwork and painted woodwork which is exposed to very hard wear or to adverse weather conditions may be protected to give it a longer lease of life by coating the work with varnish. There are many different types of varnishes used for various purposes. These types of varnishes may be divided into three main groups which are identified by the medium in which the pigments are held, and the three main groups of varnishes are known as oil varnish, spirit varnish, or water varnish.

Of these, oil varnish is most suitable for the handyman use. It is the hardest drying of the three groups — most oil varnishes are also termed ‘copal’ varnishes. Oil varnishes are slow-drying and they should not be used in very cold weather or in damp weather; and it is not advisable to use varnish for outside work on a windy day, which may result in the varnish becoming spoilt by dust. Spirit varnishes are faster drying than oil varnishes; they leave a more glossy surface finish but they are not as durable as oil varnishes for outside work.

Spirit varnishes are used mostly for finishing articles of furniture.

Water varnishes are rarely used by the decorator — their main use for the handyman is for finishing wooden toys.

Many of the different types of varnishes are named for their purpose; for instance, there is a ‘front door’ varnish, ‘church seat’ varnish, etc. The handyman-decorator is advised to state the nature of the work when purchasing varnish. The types of varnish should never be mixed in the same job; the elasticity of oil varnishes and spirit varnishes is different and if the varnishes in these two groups are used together, the surface will break up into a series of fine cracks, especially if a coat of oil varnish is followed by a coat of spirit varnish. Varnish is applied in the same way as paint; varnishes are usually applied liberally but not too thickly or runs and tears will develop.

Special attention should be paid to corners of panels, etc., to prevent the formation of runs in the finished job by overloading these parts of the work. The brushes used for varnish are slightly different from those used for applying paint. The end bristles of a varnish brush are trimmed to a point, which also shows the end shape of paint-brush bristles, so that the difference may be recognized. It is unwise to use a brush previously used for paint for applying varnish. In most cases varnish is best applied with a new brush, but if much of the work is to be done regularly, the brushes may be stored provided they are not used for other jobs.

A varnish brush is best stored, by suspending the brush from a piece of wire inserted through a hole drilled in the handle of the brush, inside a jar, which should be partly filled with varnish to cover the bristles. The jar should then be enclosed to keep it dust-proof by wrapping a piece of Cellophane over the handle of the brush and the jar holding the cover fast with string or with an elastic band.

Both interior and exterior varnishing should be done in dust-free and dry conditions. If varnish becomes damp before it dries, it will, after a period of time, develop ‘bloom’. This appears in the form of white cloudy patches which cannot be removed. The surfaces to be varnished should be well rubbed down and dusted, preferably some time before the work is done, to allow time for the dust to settle. Although varnish should be applied fairly liberally, the handyman-decorator will probably find it best in most cases, to apply two thin coats rather than one heavy one. If, as is so in most cases, two coats of varnish are applied, the first one should be rubbed down and the surface dusted before applying the finishing coat. The first coat may be rubbed down with a waterproof-grade glass-paper, or with pumice powder dusted on a soft cloth and dampened with water.

The work should be rinsed down and allowed to dry thoroughly before the finishing coat is applied. Care should be taken when applying the varnish to avoid the formation of fat edges and raised thicknesses of parts surrounding panels and mouldings, etc., due to the application of a double coat of varnish.

27. July 2011 by admin
Categories: Exterior Decorating, Treatments and Finishes | Tags: , | Comments Off on Exterior Decorating: Varnishing Exterior Woodwork


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