Surface preparation and finishing: preparing a surface by planing, scraping and sanding (working through grades of abrasive), the finishes used (varnish, wax, oil, paint, stain) and the purpose of a finish - protection and appearance.

What this dot point is asking

The SQA wants you to know how a timber surface is prepared (planing, scraping, sanding) and finished (the finishes used), and why a finish is applied. You should be able to describe the preparation steps and give the two purposes of a finish.

Preparing the surface

Good finishing depends on good preparation; a finish shows up every scratch, so the surface must be smooth first.

1. Plane the surface flat and smooth with a smoothing plane to remove saw and machine marks and high spots.
2. Scrape (with a cabinet scraper) any tricky grain a plane would tear, leaving a fine finish.
3. Sand with abrasive paper, starting with a coarser grade to remove plane/machine marks, then working through finer grades until smooth.
4. Sand with the grain, not across it, because cross-grain scratches show through the finish.
5. Remove all dust with a brush or cloth so the finish goes on cleanly.

Finishes and their uses

• Varnish - a hard, clear or tinted coat that protects well and gives a gloss, satin or matt sheen; for furniture and surfaces that take wear.
• Wax and oil - soak into the timber for a natural, low-sheen look; oil (e.g. on worktops) and wax are easy to apply and renew but protect less than varnish.
• Stain - colours the wood without hiding the grain; usually sealed with a clear varnish or oil over the top.
• Paint - an opaque coloured coat that hides the grain; protects well and gives a solid colour.

Why a finish is applied

1. Protection - seals the timber against moisture, dirt and wear, so it does not absorb water, stain or rot, and the product lasts longer.
2. Appearance - adds colour, gloss or sheen and brings out the grain, and can make the surface smoother, more hygienic and easier to clean.

Try this

Q1. State the order in which you sand a surface. [1 mark]

• Cue. Coarse grade first, then through to finer grades, sanding with the grain.

Q2. Name two finishes that could be applied to timber. [2 marks]

• Cue. Any two of: varnish, wax, oil, stain, paint.

Q3. Explain the two main reasons a finish is applied to a product. [2 marks]

• Cue. Protection (seals the timber against moisture, dirt and wear so it lasts) and appearance (adds colour, gloss or sheen and brings out the grain).