Surface Treatments for Timbers: Staining, Varnishing, Oiling, Waxing and Painting

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.

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Why Do Timbers Need Surface Treatments?

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.

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Staining

What Is Wood Stain?

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.

Application

1. Sand the timber smooth (typically 180–240 grit).
2. Apply the stain with a brush, cloth or sponge, working in the direction of the grain.
3. Allow to dry, then apply additional coats for a deeper colour.
4. Stain alone does NOT protect the timber — it must be followed with a topcoat (e.g. varnish, lacquer or oil).

Examples

• Staining pine to look like oak or walnut for a bookshelf.
• Staining MDF for a picture frame (requires a sealing coat first as MDF absorbs unevenly).

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.

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Varnishing

What Is Varnish?

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.

Types of Varnish

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

Application

1. Sand the surface smooth and remove all dust.
2. Apply thin coats with a brush or spray, allowing each coat to dry fully.
3. Lightly sand between coats (320 grit) for adhesion.
4. Apply 2–3 coats for a durable finish.

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.

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Oiling

What Is Oiling?

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.

Common Oils

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

Application