Surface Treatments & Finishes
GCSE — 2.1.2 In-depth Knowledge: Product Design
Why apply a surface finish?
Surface treatments can be applied for:
- Functional reasons — to improve the performance of the material or product (e.g. corrosion protection, water resistance)
- Aesthetic reasons — to improve the visual appearance of the material or product
Metal surface treatments
Before applying any finish, the metal surface must be prepared — dust, grease and rust must be removed. Some finishes need the surface to be keyed (roughened) to grip the finish.
| Finish | Description |
|---|---|
| Powder coating | Dry powder applied then cured in an oven — durable and colourful |
| Galvanising | Coating with zinc to prevent rust |
| Enamelling | Fusing glass powder to the metal surface — decorative and durable |
| Oil and wax finishing | Protective and enhancing finish |
| Primer and paint | Colourful protective coating; primer applied first |
| Electroplating | Depositing a thin layer of metal onto the surface (e.g. chrome plating) |
| Plastic dip coating | Metal is heated (about 200°C), dipped into a fluidised bed of polythene powder that melts onto it, then returned to the oven to cure. Used on tool handles, dish racks and garden furniture for grip, comfort, colour and corrosion protection |
| Hot blackening (black steel / oil finish) | Mild steel is heated and dipped in oil, leaving a thin black protective layer — an inexpensive finish for tools and small steel parts |
Galvanising is used on steel; non-ferrous metals such as aluminium are often anodised instead.
Surface treatment of timbers
Timber finishes are varied and include both functional and aesthetic applications depending on the location of the product.
| Finish | Description |
|---|---|
| Paint | Colourful and protective; gloss, matt or silk; applied with brush, roller or sprayer |
| Wood stain | Applied to enhance appearance; provides some protection; normally sealed with varnish |
| Oil and wax | Soak into the timber, enhance appearance and repel moisture |
| Varnish | Shiny coat applied in layers for durability; glossy or matt |
| Dip-treating | Protects surface; outdoor timber fences often use pressure-treated timber for longevity |
| Preservative | Long-lasting protection, especially for outdoor wood |
| Sealants | A sanding sealer seals the pores of the wood before varnish or polish, so fewer coats are needed |
| Primer | Seals bare wood (especially MDF edges) so paint does not soak in, and helps the top coat stick |
| Polishes | Wax polish or French polish gives a smooth, lustrous surface and enhances the grain |
Self-finishing polymers
Self-finishing — some plastics require no further finishing after forming in a mould, as the mould surface dictates the finish on the polymer.
- Vacuum forming allows a flat, glossy sheet to take the shape of the mould — the outcome duplicates the surface of the mould used
- This means no additional finishing is required if the mould surface is smooth
Textured finishes — textures such as grip patterns, leather-effect or matt surfaces can be built into the surface of a mould, so every injection-moulded or vacuum-formed product comes out already textured.
If a polymer is cut from stock, the edges are finished by draw filing, wet-and-dry paper, polishing compound or flame polishing (acrylic).
Finishing processes for papers, cards and boards
| Process | Description |
|---|---|
| Die cutting | Stamping the required shape out of a sheet using metal cutters |
| UV varnishing | Specialist high-gloss finish using ultraviolet varnish, e.g. on a business card |
| Embossing | Creates a raised pattern or shape, e.g. in a greeting card or wedding invitation |
| Debossing | Same as embossing but the feature is below the surface |
Folding process
Paper, card or board products must be folded correctly to avoid breaking or tearing:
- A crease is applied so the material bends without breaking
- A perforated line or score ensures the fold happens in exactly the right place
- Examples: greetings cards, menus, invitations, packaging
Binding products
When binding a book or pamphlet, pages must be held securely so they don’t fall out:
- Hand stitching — skilled and time-consuming; fixes pages together permanently
- Comb binding — holes punched in pages; a plastic comb holds pages in order; common and less specialist
- Perfect binding — page edges are glued into the spine of a card cover, as in paperback books and magazines
- Stapling and split pins — other common binding methods