Why are surface finishes applied, and how do the main finishing techniques work?
Surface finishing techniques: painting, powder coating, galvanising, electroplating, anodising and polishing, and why finishes are applied.
A CCEA GCSE Engineering and Manufacturing answer on surface finishing techniques, including painting, powder coating, galvanising, electroplating, anodising and polishing, and the reasons finishes are applied to engineered products.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
CCEA Unit 3 expects you to know why surface finishes are applied and how the main finishing techniques work. Finishes are added after a part is shaped, mainly to protect it and to improve its appearance.
The answer
Why apply a finish
The main finishing techniques
| Finish | How it works | Mainly for |
|---|---|---|
| Painting | A liquid coating brushed, rolled or sprayed on, then dried | Corrosion protection and colour |
| Powder coating | Dry powder applied electrostatically, then baked to a tough film | Durable, attractive coating on metal |
| Galvanising | Steel dipped in molten zinc to form a protective zinc layer | Corrosion protection of steel |
| Electroplating | A thin metal layer (e.g. chrome, nickel) deposited by electrolysis | Appearance and corrosion/wear resistance |
| Anodising | A thicker, dyed oxide layer grown on aluminium | Corrosion protection and colour on aluminium |
| Polishing | Abrasive smoothing to a shine | Appearance and a smooth surface |
Worked example: choosing a finish
Examples in context
- Example 1. Outdoor steelwork
- Crash barriers and lamp posts are galvanised so the zinc protects the steel for decades, even where stones chip the surface.
- Example 2. A bicycle frame or appliance
- Powder coated for a tough, even, coloured finish that resists chipping better than ordinary paint.
- Example 3. Aluminium window frames
- Anodised to grow a hard, coloured oxide layer that resists corrosion and weathering without paint.
The pattern is that the finish is chosen for the material and the environment: zinc for steel outdoors, anodising for aluminium, powder coat or plating where appearance and durability both matter.
Try this
Q1. Give two reasons a surface finish is applied. [2 marks]
- Cue. To protect against corrosion and to improve appearance (also wear resistance or insulation).
Q2. Why does galvanising protect steel even when scratched? [2 marks]
- Cue. Zinc is more reactive than iron, so it corrodes sacrificially in preference to the steel, protecting the exposed metal.
Q3. Which metal is anodising used on? [1 mark]
- Cue. Aluminium.
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 surface finish is applied to an engineered product, and for each reason name a suitable finish.Show worked answer →
Two reasons with a matching finish:
To protect against corrosion (rust). A suitable finish is galvanising (a zinc coating on steel) or painting, which keeps oxygen and water away from the metal.
To improve appearance. A suitable finish is polishing, powder coating or electroplating (for example chrome), which gives an attractive, smooth or shiny surface.
Markers reward two distinct reasons (corrosion protection, appearance, also wear resistance or electrical insulation) each paired with a sensible finish.
CCEA style3 marksExplain what galvanising is and why it protects steel even if the coating is scratched.Show worked answer →
Galvanising is coating steel with a layer of zinc (usually by dipping it in molten zinc). The zinc forms a barrier that keeps oxygen and water away from the steel.
It keeps protecting even if scratched because the zinc is more reactive than iron, so it corrodes in preference to the steel (sacrificial protection), continuing to protect the exposed steel rather than letting it rust.
Markers reward the description (zinc coating on steel) and the sacrificial idea (zinc corrodes instead of the iron, so a scratch is still protected).
Related dot points
- Ferrous metals (low, medium and high carbon steel, cast iron) and their composition, properties and engineering applications.
A CCEA GCSE Engineering and Manufacturing answer on ferrous metals, the carbon steels and cast iron, their composition and properties, why they rust, and where each is used in engineered products.
- Non-ferrous metals and alloys (aluminium, copper, brass) and their composition, properties and engineering applications.
A CCEA GCSE Engineering and Manufacturing answer on non-ferrous metals and alloys, including aluminium, copper and brass, their properties such as corrosion resistance and conductivity, and their engineering applications.
- Forming, casting and moulding processes: bending, folding, sand casting, die casting and injection moulding.
A CCEA GCSE Engineering and Manufacturing answer on forming, casting and moulding, covering bending and folding, sand and die casting and injection moulding, with their uses and the scales of production they suit.
- Material costs: the effect of stock form and shape and quantity on cost, and the cost and sustainability of material disposal and recycling.
A CCEA GCSE Engineering and Manufacturing answer on material costs, how the stock form, shape and quantity of a material affect price, and the cost and sustainability issues of disposal and recycling.
- Quality control and quality assurance: inspection, measuring instruments, gauges and the difference between QC and QA.
A CCEA GCSE Engineering and Manufacturing answer on quality control and quality assurance, the inspection and measuring instruments used, the role of gauges, and the difference between QC and QA.