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Surface treatments protect timber from moisture, wear and decay, and also enhance its appearance. This lesson covers the main surface treatments for timbers as required by AQA GCSE Design and Technology (8552), Section 3.2.9. You need to know what each treatment does, how it is applied, and when it is appropriate.
Timber is a natural material that is vulnerable to:
| Threat | Effect |
|---|---|
| Moisture | Causes swelling, warping and rot |
| UV light | Bleaches and degrades the surface over time |
| Insects | Woodworm and other pests bore into untreated timber |
| Fungi | Wet rot and dry rot destroy the timber structure |
| Wear | Surfaces become scratched and damaged with use |
A surface treatment creates a barrier that protects the timber and extends the product's life. The choice of treatment depends on the intended use (indoor vs outdoor), the desired appearance, and whether the natural grain should be visible.
A wood stain is a liquid that penetrates the timber surface and changes its colour while still allowing the natural grain pattern to show through. Stains are available in water-based, oil-based and spirit-based formulations.
AQA Exam Tip: A common mistake is to say that stain protects timber. It only changes the colour. You MUST apply a protective topcoat over the stain. Examiners will award marks for knowing this distinction.
Varnish is a transparent or tinted liquid that dries to form a hard, protective film on the timber surface. It is available in matt, satin and gloss finishes.
| Type | Characteristics | Typical Use |
|---|---|---|
| Polyurethane varnish | Very hard-wearing, resistant to water and scratches | Floors, tabletops, kitchen worktops |
| Acrylic varnish | Water-based, low odour, fast drying, easy clean-up | Indoor furniture, shelving |
| Yacht varnish (marine) | UV-resistant, flexible, extremely waterproof | Outdoor furniture, boats, garden gates |
AQA Exam Tip: If asked to recommend a finish for an outdoor timber product, yacht varnish or exterior-grade polyurethane varnish is the best answer because it resists UV and moisture.
Oiling is the process of applying a natural or synthetic oil to timber. The oil soaks into the grain, nourishing the wood and providing a subtle, low-sheen finish.
| Oil | Properties | Typical Use |
|---|---|---|
| Danish oil | Penetrates deeply, hardens in the wood, water-resistant | Tabletops, chopping boards, turned items |
| Teak oil | UV-resistant, flexible, repels water | Outdoor teak furniture (e.g. garden benches) |
| Linseed oil (raw) | Traditional, slow-drying, natural | Cricket bats, tool handles |
| Mineral oil (food-safe) | Non-toxic, odourless | Chopping boards, wooden spoons, salad bowls |
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