Why is finishing a product more than just making it look nice?
Apply suitable finishes to woods, metals and plastics to protect the material and improve appearance
A practical answer to the N(A)-Level D&T outcome on finishing. Finishes for wood, metal and plastic, why finishing both protects and improves appearance, the importance of surface preparation, and safe application.
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What this dot point is asking
SEAB wants you to apply suitable finishes to woods, metals and plastics, and to understand that finishing does two jobs: it protects the material and improves its appearance. The key skills are matching a finish to the material, and knowing that good surface preparation comes first.
The answer
Why finish a product
A finish is the surface treatment applied after making. It is not just decoration; it usually does two jobs at once:
- Protection. It guards the material against moisture, rust, wear, dirt or sunlight, making the product last longer.
- Appearance. It adds colour, gloss or a smooth feel, making the product more attractive and pleasant to use.
A finish can also make a product safer (sealing splinters) and easier to clean (a wipeable surface).
Finishes for each material
- Wood. Varnish (clear, protects and shows the grain), paint (colour and protection), wax or oil (a natural protective sheen), and stain (changes colour while showing grain).
- Metal. Paint (colour and a rust barrier), powder coating, plating, or oiling and lacquering to stop corrosion. Steel especially needs a finish because it rusts.
- Plastic. Often needs little finishing because it is self-coloured and smooth, but edges may be polished or buffed smooth and safe.
Surface preparation comes first
A finish only works on a surface that is clean, smooth and dry. Preparation includes:
- sanding wood smooth with abrasive paper and wiping off dust;
- cleaning grease and rust off metal;
- removing saw marks and rounding sharp edges.
Skip preparation and the finish flakes, looks uneven, or traps marks. Good preparation is most of a good finish.
Applying safely
Many finishes give off fumes or are flammable. Work in a ventilated area, follow the instructions, allow drying time between coats, and store finishes safely.
Examples in context
Example 1. A wooden chopping board. A food-safe oil finish is used because it protects the wood from water, is safe for food contact, and brings out the grain, while sealing the surface so it is easier to clean.
Example 2. An outdoor steel gate. The gate is cleaned of rust and grease, then painted in several coats; the paint forms a barrier that keeps out moisture and stops the steel rusting, while also giving an even colour.
Try this
Q1. State the two main reasons for applying a finish. [2 marks]
- Cue. To protect the material and to improve its appearance.
Q2. Name a suitable finish for a wooden item that should still show its grain. [1 mark]
- Cue. A clear varnish, wax or oil.
Q3. Explain why surface preparation is done before applying a finish. [3 marks]
- Cue. Because a finish only sticks well and looks even on a clean, smooth, dry surface; without preparation it flakes, looks uneven or traps dust and marks.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksExplain two reasons for applying a finish to a product. Then name a suitable finish for (a) a wooden toy and (b) a steel garden tool, giving a reason for each.Show worked answer →
Two reasons: (1) to protect the material, for example from moisture, rust or wear; (2) to improve appearance, for example adding colour or a smooth, attractive surface. A finish can also make a product easier to clean or safer to handle.
(a) Wooden toy: a non-toxic varnish or child-safe paint, because it protects the wood from moisture and handling, looks attractive, and is safe in a child's mouth.
(b) Steel garden tool: paint or a coating (or oiling the metal), because steel rusts outdoors and the finish forms a barrier that keeps out moisture and prevents rust.
What markers reward: two clear reasons (protection and appearance), and a suitable finish for each item with a reason linked to the material's needs (safe and protective for the toy, rust prevention for the steel).
Original4 marksExplain why a surface must be prepared properly before a finish is applied, and describe one way to prepare it.Show worked answer →
A finish only sticks well and looks good if the surface is clean, smooth and dry first. If dust, grease or rough patches are left, the finish can flake off, look uneven or trap marks. One way to prepare wood is to sand it smooth with abrasive paper and wipe off the dust; for metal, clean off grease and rust before painting.
What markers reward: the point that preparation lets the finish stick and look even (poor preparation causes flaking or an uneven finish), and a correct preparation method such as sanding wood smooth or cleaning metal.
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