Wood Finishing: Preparation, Staining and Grain Filling

Preparation

Correct preparation is essential for any wood finish. Modem clear finishes in particular accentuate scratches and other imperfections, if not removed. Get as fine a finish as possible with the cutting tools to keep sanding to a minimum, especially on hardwood. After planing wood, or scraping a veneered surface with a cabinet scraper, sand carefully to remove any tool marks, torn grain or glue.

For sanding, wrap the paper around a flat cork block; an odd scrap of wood is not really suitable. Garnet or Lubrisil papers require less effort than glass-paper, but they cost more and are not always readily obtainable.

Sand with a firm, moderate pressure, and keep the block in a straight line with the direction of the grain.

Remember that you are trying to get the surface flat as well as smooth, so occasionally alternate the angle of the block to the work but continue to work it in the direction of the grain.

Sunlight darkens newly finished wood. On no account leave anything standing on a freshly sanded surface; it will cause a light patch which must be re-sanded.

Veneers are exceptionally thin, so take great care when scraping or sanding, particularly on the corners.

sandpaperWork down through three grades of abrasive paper, starting with a reasonably coarse grade, following with a medium grade and finishing with a fine paper.

After sanding, use a fine brush to remove grit and dust from the surface of the work, brushing in the direction of the grain to ensure that crevices are clear.

Power orbital sanders are useful for finishing but require experience to use, especially on veneers. Do not use sanding discs or portable belt sanders unless the work is to be painted.

Fill irremovable blemishes, such as panel pin holes, splits and small knots, with a stopping such as Brummer Yellow Label, which can be bought in a range of colours to match most timbers.

Press the stopping into the hole, taking care not to spread it into the grain beyond the immediate blemish. Let the stopping dry, then sand it flat.

If a small item is to be finished, protect the bench from becoming stained by covering it with hardboard; if the work is large, raise it off the floor on blocks or place it on sawing stools.

Finishes cannot be applied successfully in all temperatures: 18-21°C (64-70°F) is ideal for most operations. Do not attempt finishing in cold or damp conditions.

Do not carry out staining and colouring in artificial light. Plenty of daylight is advisable, but not direct sunlight.

Before starting, sand off sweaty finger marks and have plenty of clean, non-fluffy cotton cloth available.

Cleanliness is essential, so remove all dust from the bench and floor before starting work.

 

Staining

Before finishing timber, you may want to stain it. It is better not to stain new work; nearly all timbers are more attractive when left natural, and the process of staining is tricky unless you have had experience. But it may be necessary when repairing old furniture or when a new item has to be matched with existing furniture.

Stains are readily available, in a variety of shades, from ironmongers and do-it-yourself shops. If possible, select the type of stain recommended by the manufacturer of the finish you intend to use. With so many chemical finishes available, this eliminates the risk of a reaction setting in between the stain and the finish.

If in doubt, choose a water stain. This will not cause a chemical reaction, but the wood will require sanding after application of the stain as water stains raise the grain.

Before staining, experiment on an odd piece of the same timber, carefully sanded, to make sure that you have the shade required. Allow the stain to dry, then apply a coat of finish; this will further darken and enrich the colour.

To achieve a particular shade, stains can be mixed, provided they are of the same type and from the same manufacturer. Mix enough at one time to complete the whole job, as it is difficult to mix two batches to exactly the same shade.

Application: working quickly with a soft, dry, non-fluffy cloth or brush, apply a liberal, even coat over the whole surface, taking care to work in the direction of the grain.

Wipe off the excess with a clean, dry cloth, working evenly and with the grain, before the stain has dried. When working on a large area, take care that drying out does not occur before the whole surface has been covered with stain, otherwise the final colouring will be uneven.

When dry, wipe the surface again with another dry cloth before applying any finish.

Take care not to spill drops of stain on untreated surfaces as these will penetrate deeply and show as dark patches.

Grain filling

Grain fillers fill the pores of the timber and give the finish a flat, mirror-like surface, as in French polishing. Today the tendency is to leave timber looking as natural as possible so that the texture of the grain can be seen and felt. For this reason, fillers are often dispensed with.

Fillers should not be used for oil, wax or limed finishes, but they are advisable before French polishing and for some open-grained timbers, such as oak or rosewood, when a heavily brushed or sprayed lacquer is to be applied.

Application: use the grain filler recommended by the manufacturer of the finish that you intend using. Read the maker’s instructions: some fillers require thinning.

Apply the shade required liberally by brush or rag, working it into the surface with a circular motion and finishing off across the grain; wipe off the surplus and allow to dry.

When thoroughly hard and dry, sand lightly with the grain.

29. June 2011 by admin
Categories: Treatments and Finishes, Woodworking | Tags: , | Comments Off on Wood Finishing: Preparation, Staining and Grain Filling

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