Finishing and Preservation: notes

Why finish wood

A finish protects wood from moisture, dirt and damage, and improves its appearance.

Preparing the surface

• Planing and scraping: remove marks left by tools.
• Glasspaper: sand with the grain, from coarse to fine grades, never across it. Wrap the paper round a cork block for flat surfaces.
• Filling: fill nail holes and small gaps with wood filler or stopping, then sand level.

Types of finish

• Paint: hides the grain. Apply primer first, then undercoat, then gloss. Each coat must dry and be lightly sanded.
• Varnish and polyurethane: clear coats that show the grain and give a hard, shiny, water resistant film.
• Wax: gives a soft shine but little protection. Oil: soaks in and feeds the wood.
• French polish: shellac rubbed on in thin coats for a high gloss on fine furniture.
• Stain: changes the colour while keeping the grain visible; a clear coat goes over it.
• Brushes: clean with the right solvent: water for water based paint, white spirit for oil based paint.

Preservation

• Termites and woodworm: insects that eat timber. Treated timber resists them.
• Fungal rot: wet or damp wood rots. Keep timber dry and ventilated.
• Preservatives: creosote is painted on fence posts. Pressure treated (tanalised) timber is soaked deep by the process.
• Veneers and laminates: a thin layer of fine wood or plastic glued over a cheaper board.