Why are surfaces finished, and which finish suits each material?
Finishing techniques: why surfaces are finished, and finishes for timber, metal and plastic - varnish, paint, oil, polish, anodising, plating and self-finishing.
A CCEA GCSE Technology and Design answer on finishing techniques: why surfaces are finished, surface preparation, and the finishes used for timber, metal and plastic, including varnish, paint, oil, polish, anodising, plating, and self-finishing materials.
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What this dot point is asking
CCEA wants you to explain why surfaces are finished and to match a suitable finish to timber, metal or plastic. You should know preparation, common finishes, and the idea that some materials are self-finishing and need no extra treatment.
The answer
Why surfaces are finished
A good answer always links the finish to these purposes: an outdoor metal product is finished to stop it rusting; a wooden toy is finished so it is smooth and safe to handle.
Preparing the surface
Most finishes need the surface prepared first. Timber is sanded smooth (working through finer grades of abrasive paper). Metal is filed and rubbed with emery cloth, and may be cleaned (degreased) so the finish bonds. Good preparation is essential, because a finish applied to a rough or dirty surface will look poor and may not stick.
Finishes for timber
Finishes for metal
Ferrous metals especially need a finish, because they rust; protecting the surface from air and water is the key job.
Finishes for plastic and self-finishing materials
Worked example: choosing finishes for a product
Examples in context
- Example 1. A wooden salad bowl
- Finished with a food-safe oil that soaks in, repels water and shows the grain, protecting the timber while keeping it safe for food contact.
- Example 2. Aluminium phone case
- Anodised to give a hard, coloured, scratch-resistant surface - a finish only aluminium can take by this process.
- Example 3. An acrylic display stand
- Self-finishing plastic needing no coating; only the cut edges are filed and buffed to a clear shine, showing the advantage of polymers.
Being able to give the reasons for finishing and pick a finish that matches the material and its use lets you answer both "why finish" and "describe a suitable finish" questions.
Try this
Q1. Give two reasons why a product is given a surface finish. [2 marks]
- Cue. To protect the material (rust, rot, wear) and to improve its appearance.
Q2. Name a suitable finish for an aluminium product. [1 mark]
- Cue. Anodising (or electroplating, paint or powder coating).
Q3. What does it mean to say a plastic is self-finishing? [1 mark]
- Cue. It is already smooth, coloured throughout and resistant to moisture, so it needs no extra finish.
Q4. Why must a ferrous metal be finished if used outdoors? [2 marks]
- Cue. It contains iron and will rust in rain and air, so a finish seals the surface to prevent corrosion.
Q5. What preparation is needed before varnishing timber? [1 mark]
- Cue. Sanding the surface smooth (working through finer grades of abrasive paper).
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA style4 marksGive two reasons why a product is given a surface finish.Show worked answer →
To protect the material from damage and from the environment, such as preventing wood from rotting or metal from rusting (1), which makes the product last longer (1).
To improve the appearance, for example adding colour, gloss or a smooth feel (1), which makes the product more attractive and pleasant to handle (1).
Markers also accept making it easier to clean or safer to handle.
CCEA style4 marksDescribe a suitable finish for an outdoor steel gate and explain why it is suitable.Show worked answer →
The steel could be painted, for example with a primer then a top coat or a galvanised then painted finish (1). The gate is ferrous and outdoors, so it would rust without protection (1).
Paint (over a primer, or galvanising which coats the steel in zinc) seals the surface from rain and air to prevent rusting (1) and also gives colour and improves appearance (1).
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A CCEA GCSE Technology and Design answer on scales of production - one-off, batch and mass (and continuous) production - and the aids to manufacture that make repeated parts accurate: jigs, moulds, fixtures, templates and patterns.
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Sources & how we know this
- CCEA GCSE Technology and Design specification — CCEA (2017)