Surface Treatments and Finishes

Surface Treatments and Finishes

Surface treatments and finishes are applied to products to improve their appearance, protect against wear and corrosion, or enhance functionality. AQA GCSE D&T requires you to know methods for timber, metal, polymer, and textile materials.

Why Apply a Finish?

Finishes serve one or more of these purposes:

• Protection — against moisture, corrosion, UV degradation, wear, rot, insects
• Aesthetics — colour, gloss, texture, pattern, visual appeal
• Function — non-stick coating, electrical insulation, grip, hygiene
• Identification — colour coding (e.g. electrical wires, plumbing pipes)

Timber Finishes

Finish	Type	Properties	Application	Suitable For
Varnish	Protective, clear	Waterproof, hard-wearing, available in matt/satin/gloss	Brush or spray	Indoor furniture, floors
Paint	Protective + decorative	Waterproof, wide colour range, hides grain	Brush, roller, or spray	Indoor/outdoor timber, MDF
Wood stain	Decorative	Penetrates the grain, changes colour while showing grain pattern	Brush or cloth	Furniture, cladding
Oil (tung, linseed, Danish)	Protective	Penetrates wood, enhances grain, natural feel, needs reapplication	Cloth or brush, multiple coats	Kitchen utensils, worktops, outdoor furniture
Wax	Protective + decorative	Soft sheen, enhances grain, not waterproof, needs reapplication	Cloth, buffed by hand	Antique furniture, turned items
Preservative (creosote, Cuprinol)	Protective	Prevents rot, insect attack; penetrates deeply	Brush or pressure-treated	Fences, decking, sheds
Laminating / veneering	Decorative + protective	Thin layer of high-quality wood or plastic bonded to surface	Adhesive + press	Chipboard furniture, kitchen doors

Preparation for timber: Sand through grades (coarse to fine: P80 → P120 → P240), remove dust, apply primer/sealer if painting.

Metal Finishes

Finish	Type	Properties	Application
Painting / powder coating	Protective + decorative	Wide colour range; powder coating gives tough, even finish	Spray paint or electrostatic powder + oven curing
Galvanising	Protective	Zinc coating prevents rust; sacrificial protection	Hot-dip (immersion in molten zinc)
Electroplating	Protective + decorative	Thin layer of one metal deposited onto another using electrolysis	Electrolytic bath (e.g. chromium plating on steel)
Anodising	Protective + decorative	Thickens the natural oxide layer on aluminium; can be dyed	Electrolytic process (aluminium only)
Lacquering	Protective	Transparent coating, prevents tarnishing	Brush or spray
Oil / grease	Protective (temporary)	Prevents rust during storage and transport	Applied by hand or dip
Enamelling	Protective + decorative	Glass-like finish fused to metal surface; hard, colourful	Powdered glass applied then kiln-fired
Blueing	Protective + decorative	Controlled oxidation giving blue-black finish	Chemical dip or heat treatment

Preparation for metals: Degrease, remove rust/scale (wire brush, emery cloth, pickling), apply primer if painting.

Sacrificial protection (galvanising): Zinc corrodes preferentially instead of the steel beneath, because zinc is more reactive. Even if the zinc coating is scratched, the steel is still protected as long as zinc remains nearby.

Polymer Finishes

Polymers often require less finishing than timber or metal because they can be coloured during manufacture (pigments mixed into raw material). However, some finishes are used:

Finish	Description	Use
Polishing / buffing	Mechanical smoothing to high gloss	Acrylic display cases, jewellery
Printing	Screen printing, pad printing, digital printing on surface	Labels, logos, patterns on casings
Self-coloured	Pigment added to raw polymer before moulding	Most plastic products
Vinyl wrapping	Adhesive film applied over surface	Phone cases, vehicle panels
Painting	Specialist plastic primers + paint	Custom colours on ABS, nylon
Hydrographic printing (water transfer)	Pattern film transferred via water immersion	Camouflage, carbon-fibre effect on helmets

Textile Finishes

Finish	Type	Effect	Example
Dyeing	Decorative	Adds colour throughout the fabric	Tie-dye, vat dyeing, reactive dyeing
Printing	Decorative	Applies colour/pattern to the surface only	Screen printing, digital printing, block printing
Brushing / raising	Aesthetic	Creates a soft nap on the surface	Fleece, brushed cotton
Calendering	Functional + aesthetic	Rollers press fabric for smooth, glossy finish	Chintz fabric
Laminating	Functional	Bonding a membrane to fabric	Gore-Tex (waterproof + breathable)
Mercerising	Functional	Treating cotton with NaOH to increase lustre and strength	High-quality cotton shirts
Flame retardant	Functional (safety)	Chemical treatment to resist ignition	Children's nightwear, curtains, upholstery
Water repellent (DWR)	Functional	Chemical coating causes water to bead and roll off	Outdoor jackets, tents
Anti-static	Functional	Reduces static charge build-up	Synthetic workwear, electronics packaging
Stain resistant	Functional	Coating repels liquids and prevents absorption	Scotchgard on upholstery

Paper and Board Finishes

• Laminating — thin plastic film heat-sealed to surface (gloss or matt); protects, waterproofs
• Varnishing — spot varnish (selective areas for contrast) or flood varnish (entire surface)
• Embossing / debossing — raised or recessed pattern pressed into surface
• Foil blocking — metallic foil pressed onto surface with heated die (luxury packaging)
• UV coating — liquid applied then cured with UV light; hard, glossy, scratch-resistant

Exam Tips

• When recommending a finish, always state why it is suitable — link to protection, aesthetics, or function
• Know at least two finishes for each material category (timber, metal, polymer, textile)
• Questions often ask you to compare finishes — use a table comparing durability, cost, appearance, and suitability
• For metals, understand the difference between galvanising (sacrificial, zinc) and electroplating (decorative, thin layer)
• Preparation is often worth marks — mention sanding, degreasing, or priming where relevant
• Anodising is aluminium only — do not suggest it for steel or other metals

Key Definitions

• Surface finish: A treatment applied to the exterior of a product to protect, decorate, or improve its functionality
• Galvanising: Coating steel with zinc to prevent corrosion through sacrificial protection
• Anodising: An electrolytic process that thickens the oxide layer on aluminium, allowing it to be dyed
• Electroplating: Depositing a thin layer of metal onto another metal using electrolysis
• Laminating: Bonding a thin protective layer (plastic film, veneer, or membrane) to a surface