Wood Finishing Tips

When using stains and varnishes, the technique depends on the type of material.

Board finishing

The plywood facing of blockboard and the surface of pine-board can be stained, polished or varnished without preparation other than sanding. This also applies, of course, to veneered chipboard and plywood, but plain chipboard needs some degree of filling, or preferably veneering, before a suitable finish can be applied.

Cut edges of chipboard can be a problem, but they can be trimmed using iron-on veneer strips which are obtainable in finishes to suit the finish of the boards you are using. Careful planning will enable you to use standard sizes and therefore reduce the number of cut edges. You can also arrange for the cut edges to be at the back, where they will be covered by the hardboard back of the unit, or in a position where they will be covered by other boards.

When plain chipboard is being used and is to have a decorative laminate applied to it, it is important that a similar laminate, which will be cheaper because it is not decorative, is applied to the back as well. Without this balancing veneer, the chipboard will tend to bend. However, the balancer is not essential when the board is being used for worktops or table tops because these can be screwed securely to the frame which will restrain it. Unlike natural timber, chipboard does not need to have the freedom to move with the changes in the atmosphere’s relative humidity.

Timber finishing

All articles made of wood need treating with a preservative or finish, not only to preserve and protect the surface, but also to bring out the inherent beauty of the grain and the texture of the timber. The quality of finish is extremely important, as it is by this that the work is usually judged. Although painting will hide any slight surface defects any blemish in wood becomes even more noticeable when a clear finish, or a stain and clear finish are applied. It is important also that all woodwork except that which is being treated with a preservative such as creosote, is perfectly clean and smooth.

The main processes in finishing are filling, stopping, staining and applying the finish. When a clear finish is to be applied, it is essential when an orbital electric sanding machine has been used that the surface is still finished afterwards by sanding with the grain, by hand. If this is not done, small circular scratches resembling fish scales will be seen in the final coat.

Preservatives

Fences and sheds can be treated with creosote to BS 3051. If the brown colour is not acceptable, preservative of another colour can be used. Where the timber will

be in contact with plants, such as on the inside of greenhouses and forcing frames, a green horticultural preservative should be used. Colourless preservatives are also available, for use on interior and exterior woodwork; these can be painted when dry.

Painting

Emulsion paint can be applied direct to sanded wood and no knotting, primer or undercoat is required. Before applying solvent-based paints, any knots in the wood should be sealed with pure shellac knotting and allowed to dry. Any cracks or dents should then be filled with wood-stopping, which should be applied slightly proud of the surface to allow for shrinkage and, when dry, papered smooth. Next, a pink or white primer, followed by an undercoat of a similar colour to the top coat, should be applied. If a first-class finish is required, lightly rub this smooth with fine glasspaper when it is dry, and apply a second coat. This too can be rubbed down before applying the finishing coat.

Because paint is pigmented it does not usually have as good a flow as varnish and, to make sure that no brush marks are left on the surface, it should be `laid-off’ to a greater extent than a varnish. The paint should be applied in one direction, then with a slightly lighter pressure at right

angles, then with lighter pressure still diagonally, finishing off with the minimum pressure, drawing the brush lightly across the surface in the original direction of application.

The best results are always obtained by using good quality brushes of the correct size. For example, it is no good using a 1” brush for painting a door — a 21/2” brush would be more suitable. Immediately after use, brushes should be cleaned with white spirit or a proprietary solvent.

Exterior wood-stains can be used on timber instead of paint. These are not to be confused with the transparent wood-stains or dyes used for staining wood prior to the application of clear finishes. They contain a

pigment and tend to obliterate the grain, but they are easy to apply and maintain.

Non-pigmented finishes

All finishes alter the colour of wood to some extent and some woods, for example, mahogany and walnut, turn much darker even when a completely clear finish is applied. An approximate idea of the colour the wood will become when finished with a clear solution can be seen by damping a small area with water. If this colour is too light, then the wood can be stained before finishing. It is only possible to stain wood to a darker colour; for a lighter shade it must be bleached.

When staining wood, it is advisable to

test the stain on a square piece of wood, or on an area which would not normally be seen as it is difficult to remove stain which has been recently applied. If the wood has an open grain, and a smooth finish is required, then a grain-filler should be used for filling the pores, or extra coats of the finish would have to be applied and then rubbed down with an abrasive paper. Any cracks or holes in the wood should be filled with wood-stopping before staining.

The final finish may be of a type which leaves a surface film, such as French polish, varnish or polyurethane. The last two are available in gloss, satin and matt finishes. Varnish stains are also available which will colour and finish the wood in one operation. It is important to note, however, that each extra coat of varnish stain will darken the colour and, unless brushed out very evenly, the colour will vary as the thickness of the film varies. When wood is stained with a penetrating dye, the colour will not vary however many coats of clear finish are then applied. When varnishing an external door, it is important that at least one coat is applied to the top, bottom and side edges to prevent water being absorbed at these

points, which would eventually cause the varnish to fail.

Alternatively, oiled finishes may be used, such as teak oil and Danish oil. These finishes are far easier to apply than the previous types as they are merely wiped over the surface with a cloth. Teak oil leaves the wood with a soft, lustrous finish. When a high gloss finish is required on exterior woodwork, a yacht varnish should be used. These usually contain tung oil which has outstanding exterior durability.

Waxing

This type of finish is popular on wood such as pine and oak. Before applying wax the wood should be sealed with French polish if a golden colour is required, or with

transparent French polish, which will not alter the colour of the wood. Two coats of French polish should be applied with a brush or rag and, when dry, lightly rubbed down with fine glasspaper. The surface can also be rubbed down with fine steel wool and wax polish. This treatment will give an acceptable satin finish. If, however, a higher gloss is required, then the wax polish should be applied with a soft cloth or a shoe polishing brush and allowed to harden. The surface should then be buffed with a soft yellow duster or soft shoebrush.

French polishing

For further information on this process send a stamped addressed envelope to the manufacturer of the product.

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