Surface Preparation, Finishing and Polishing
Scope
This domain tests the sequence from a machined surface to a finished one, the materials used, and the faults that appear in a finish.
Preparation
- Remove machine marks with a finely set smoothing plane or a cabinet scraper, working with the grain.
- Sand in sequence 80 → 120 → 180 → 240 grit; never skip a grit.
- Raise the grain with a damp cloth, let it dry, and sand lightly again.
- Fill defects with stopping or glue-and-sawdust; fill open pores with paste filler on coarse-textured timbers.
- Check moisture content - never finish above about 12–14%, or the film will blush and lift.
Finishing materials
- French polish: shellac dissolved in methylated spirit, applied with a rubber (cotton wool wrapped in linen) in overlapping circles then straight strokes.
- NC and PU lacquer: sprayed or brushed; PU is harder and more water-resistant.
- Melamine, wax, oil, varnish; stains (water, spirit, oil); bleach for evening colour.
Worked example
French polishing a teak panel: sand to 240, damp-and-sand, apply filler, seal with a thin coat of polish, then charge the rubber lightly and work in circles followed by strokes along the grain, adding spirit only as the rubber dries. Leave overnight, de-nib with 600 grit, and body up to the required gloss.
Traps
Sanding across the grain and leaving scratches that show under polish; too much oil or spirit on the rubber, giving a patchy or sticky finish; finishing over dust; applying a hard film to a damp surface.