How are products protected and finished, and how are their parts joined together?
Surface finishes and methods of joining: finishes applied to timbers, metals and polymers and why they are used, and permanent and temporary fixings and fittings, including knock-down fittings.
An SQA Higher Design and Manufacture answer on surface finishes and methods of joining, covering finishes for timbers, metals and polymers and why they are applied, and permanent and temporary fixings and fittings including knock-down fittings used in flat-pack products.
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What this key area is asking
The SQA wants you to know why finishes are applied to products and which finishes suit timbers, metals and polymers, and to know the methods of joining parts - permanent fixings and temporary (including knock-down) fittings - and when each is used. The question paper asks you to explain the purpose of a finish and to justify a joining method, often for the flat-pack context, usually for 3 to 5 marks.
Why products are finished
Most materials need finishing because they would otherwise be damaged or look unappealing. Untreated timber absorbs moisture, marks and wears; ferrous metals rust; surfaces may be rough or the wrong colour. A finish solves these while letting the designer control colour and texture for the market.
Finishes for each material
Timbers. Take a range of finishes that seal and decorate the grain:
- Varnish and lacquer - clear, hard protective coat that resists moisture and wear.
- Paint - covers the grain and gives any colour, protecting and decorating.
- Stain and oil - colour or feed the wood while showing the grain, used on quality furniture.
- Wax - a soft protective sheen.
Metals. Mainly to prevent corrosion and to colour:
- Paint and powder coating - protect (especially ferrous metals from rust) and colour; powder coating is tough and even.
- Galvanising - a zinc coating that protects steel from rust, used outdoors.
- Anodising - thickens the oxide layer on aluminium, hardening it and allowing colour.
- Plating - a thin layer of another metal (such as chrome) for protection and appearance.
Polymers. Many plastics are self-finished: they are coloured throughout and come out of the mould smooth, so they often need no extra finish, which is one reason plastics are cheap to mass-produce.
Joining methods: permanent and temporary
The choice depends on whether the joint must ever come apart, the materials, and the scale:
- Permanent joints suit products that stay assembled and need maximum strength: a welded steel frame, a glued timber joint, a riveted panel.
- Temporary joints suit products that must be assembled by the user, dismantled for repair, or flat-packed: bolted machine parts and knock-down (KD) fittings in board furniture.
Knock-down fittings (such as cam locks, threaded inserts and corner blocks) are tightened with simple tools and can be undone, so they let cheap board furniture be sold flat and built at home, cutting transport and packaging cost.
Where this fits in the course
Finishes, fixings and fittings complete the Materials and Manufacture area: once a material and process are chosen, the product must be finished and assembled. The question paper asks the purpose of finishes and the choice of joining method (knock-down fittings come up often), and your design assignment must specify finishes and joining for your outcome.
Try this
Q1. Explain two reasons a wooden garden bench is given a finish, and name a suitable one. [4 marks]
- Cue. To protect it from moisture and rot and to improve appearance; an exterior varnish, oil or paint suits.
Q2. Explain why galvanising is used on outdoor steel products. [3 marks]
- Cue. Steel is ferrous and rusts; the zinc coating protects it from corrosion so it survives outdoors.
Q3. Explain why a designer might choose temporary fittings rather than permanent joints for a piece of furniture. [3 marks]
- Cue. Temporary fittings (including knock-down) let the product be flat-packed, assembled by the user and dismantled for moving or repair.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher4 marksExplain why a finish is applied to a product, using one timber and one metal example.Show worked answer →
Worth about 4 marks, so the marker wants the purpose of finishing applied
to both a timber and a metal. The mark scheme rewards protection and
appearance linked to the material.
Timber example. A finish such as varnish or oil is applied to a wooden
table to protect it from moisture, dirt and wear and to enhance the grain
and appearance, because untreated timber absorbs water and marks easily.
Metal example. A finish such as paint, powder coating or galvanising is
applied to mild steel (for example a gate) to protect it from corrosion,
because ferrous metals rust, and to give a chosen colour and appearance.
A strong answer states the two main reasons for any finish: to protect the
material (from moisture, corrosion or wear) and to improve appearance, and
notes finishes can also improve grip or hygiene.
SQA Higher4 marksExplain why knock-down fittings are used in flat-pack furniture.Show worked answer →
Worth about 4 marks. The markers want the benefits of knock-down fittings
linked to flat-pack manufacture and sale.
Flat-pack transport and storage. Knock-down fittings let the furniture be
sold in pieces and assembled by the customer, so it packs flat, which cuts
packaging, storage and transport costs and makes it easier to carry home.
Assembly without skill or glue. Fittings such as cam locks and threaded
inserts are tightened with simple tools, so the customer can assemble the
product without skilled joinery or waiting for glue to set.
A strong answer adds that the joints can be undone, so the product can be
flat-packed again if moved, and that this suits cheap, mass-produced
board furniture.
Related dot points
- Timbers used in product design: natural hardwoods and softwoods and manufactured boards, their key properties (strength, hardness, durability, workability, finish, cost) and how those properties guide material choice.
An SQA Higher Design and Manufacture answer on timbers, covering natural hardwoods and softwoods and manufactured boards, their key properties such as strength, durability, workability and cost, and how a designer matches a timber to the demands of a product.
- Metals used in product design: ferrous and non-ferrous metals and alloys, their key properties (strength, hardness, ductility, malleability, conductivity, corrosion resistance, cost) and how those properties guide material choice.
An SQA Higher Design and Manufacture answer on metals, covering ferrous and non-ferrous metals and alloys, their key properties such as strength, ductility, conductivity and corrosion resistance, and how a designer matches a metal to the demands of a product.
- Polymers used in product design: thermoplastics and thermosetting plastics, their key properties (formability, strength, toughness, durability, finish, cost) and how those properties guide material choice.
An SQA Higher Design and Manufacture answer on polymers, covering thermoplastics and thermosetting plastics, their key properties such as formability, toughness and durability, common examples and uses, and how a designer matches a polymer to the demands of a product.
- Manufacturing processes for shaping materials: moulding and forming processes for polymers, casting and forming processes for metals, and cutting, shaping and joining for timbers, and matching a process to the material, form and scale of production.
An SQA Higher Design and Manufacture answer on manufacturing processes, covering moulding and forming of polymers (injection moulding, vacuum forming, blow moulding), casting and forming of metals, and shaping and joining of timbers, and how a designer matches a process to the material, the form and the scale of production.