Mini-Lesson

The Use of Finishes

This mini-lesson covers finishes — why we apply them and the main treatments for timber (varnish, oil, stain), metal (powder coating, electroplating, anodising, galvanising) and polymers (self-finishing).

Work through each screen, answer the questions as you go and collect ⭐ stars. Press Start when you’re ready.

Overview

Why apply a finish?

A finish is a surface treatment applied after manufacture. It has four main jobs:

Protection — resist corrosion, moisture, UV, abrasion and wear.
Aesthetics — colour, gloss, texture and brand identity.
Hygiene — a sealed, wipe-clean surface.
Function — grip, electrical insulation or reduced friction.

Preparation is everything: a finish is only as good as the surface beneath it — cleaning, degreasing, sanding and priming come first.

Timber finishes

Finishing timber

Varnish / lacquer — a clear, hard, protective film that shows the grain.
Paint — opaque colour plus protection (needs a primer/undercoat).
Oil (teak/Danish) and wax — soak in to nourish and give a natural, water-resistant sheen.
Stain — changes colour while showing grain; often sealed with varnish.
Preservative — protects exterior timber from rot, fungi and insects.

Quick check

Finishing an outdoor bench

?Which combination best protects a softwood garden bench that will stay outside all year?

Calculate

Your turn — paint coverage

∑A tin of paint covers 12 m² per litre. You need to coat a total surface area of 30 m² with one coat. How many litres are required?

litres

Hint: litres = area ÷ coverage = 30 ÷ 12.

Metal finishes

Finishing metals

Painting & powder coating — powder coating sprays charged powder electrostatically, then bakes it to a tough, even film.
Electroplating — an electric current deposits a thin metal layer (e.g. chrome, nickel) for protection and shine.
Anodising — thickens the natural oxide layer on aluminium; hard-wearing and can be dyed a colour.
Galvanising — dipping steel in molten zinc; the zinc corrodes in preference to the steel (sacrificial protection).
Dip coating — a warmed part is dipped in polymer powder for a plastic coating (tool handles, wire racks).

Match it

Match finish to its job

Tap a finish, then tap what it does / what it suits.

Term

Match

Quick check

How does galvanising protect steel?

?A galvanised steel bucket is scratched to bare metal but still does not rust at the scratch. Why?

Quick check

Anodising

?Which statement about anodising is correct?

Polymer finishes

Polymers: self-finishing

Most polymers are self-finishing — the mould gives the final surface texture and gloss, and colour is added as pigment in the granules, so no extra coating is needed. Surfaces can still be printed, textured or flocked for grip or decoration.

Health & safety

Finishing safely

Many finishes give off solvents and fine spray. Apply paints and lacquers in a ventilated spray booth, wear appropriate PPE (respirator, gloves, eye protection) and follow COSHH guidance for hazardous substances.

Sort it

Timber or metal finish?

Tap a finish, then tap the material it is used on.

🌳 Timber finish

⚙️ Metal finish

Recap

The big ideas to know

Four jobs: protection · aesthetics · hygiene · function.

Prep first: clean, degrease, sand, prime — a finish is only as good as the surface.

Timber: varnish, oil, wax, stain, preservative.

Metal: painting/powder coating, electroplating, anodising (Al), galvanising (Zn, sacrificial).

Polymers: usually self-finishing from the mould, self-coloured.

Coverage: litres needed = area ÷ coverage per litre.

You’ve covered the key ideas for this topic. Press Finish to see your score.

🏆

Mini-lesson complete!

⭐⭐⭐

You’ve worked through The Use of Finishes for AQA A-level Product Design (7552). 🎉

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