Machines, materials & finishing · National 5
Surface preparation & finishes
9 cards · 5 quiz · 0 exam
Practical Woodworking · National 5 · mrkellydt.co.uk
What you're learning in this topic
Learning intention WALT
We are learning about surface preparation & finishes, specifically to be able to:
- prepare a surface by planing, scraping, stopping and sanding
- choose a suitable finish: varnish, stain, wax or oils
- apply a finish evenly to every surface
Success criteria WILF
- I can prepare a surface by planing, scraping, stopping and sanding
- I can choose a suitable finish: varnish, stain, wax or oils
- I can apply a finish evenly to every surface
Preparing the surface
- Plane surfaces smooth (smoothing plane).
- Scrape with a cabinet scraper to remove tears and plane marks, especially on difficult grain.
- Stop (fill small holes and cracks with wood stopper/filler matched to the colour of the wood) and let it dry.
- Sand with abrasive paper wrapped round a cork block, with the grain, working from coarse to medium to fine.
- Remove dust with a brush or tack cloth before finishing.
Glass paper is cheaper; garnet paper is harder and lasts longer. Grades: coarse, medium, fine.
In the practical activity, don't put filler or finish over joints before they've been verified.
Finishes
| Finish | Properties |
|---|---|
| Varnish (polyurethane) | Tough, waterproof film; clear or coloured; gloss, satin or matt. Several coats, rubbed down between coats |
| Stain | Changes the colour of the wood but doesn't protect it, so it needs varnish or wax on top. Advantage over varnish: changes colour while showing the grain, and it soaks in so it doesn't chip |
| Wax | Soft sheen, enhances grain, easy to apply; little protection; needs re-applying |
| Danish oil | Soaks in and hardens; natural look; good for hardwoods and turned work |
| Linseed oil | Traditional oil; slow drying; outdoor use and cricket bats |
| Vegetable oil | Food-safe: chopping boards, salad bowls and kitchen utensils |
Applying a finish
- Apply with a brush or lint-free cloth, with the grain, in thin even coats.
- Let each coat dry, then rub down lightly with fine abrasive or wire wool before the next.
- Cover every surface for full marks, with no runs, drips or missed areas.
- Work in a ventilated area; wear gloves for stains and oils. Oily rags can self-ignite: lay them flat to dry or put them in a metal bin.
Key terms
| Order of abrasive grades | Coarse, then medium, then fine |
|---|---|
| Sanding direction | With the grain |
| Stopping | Filling small holes or cracks with wood stopper |
| Scraping | Using a cabinet scraper to remove tears and plane marks |
| Garnet paper vs glass paper | Garnet is harder and lasts longer |
| Stain | Changes colour but doesn't protect: needs varnish or wax on top |
| Varnish | Tough waterproof film |
| Food-safe finish | Vegetable oil |
| Advantage of stain over varnish | Changes colour while showing the grain; soaks in so it won't chip |
Quick check
1. Which finish is food-safe for a chopping board?
- Varnish
- Wax polish with solvent
- Stain
- Vegetable oil
Show answer
D: Vegetable oil. Vegetable oil is safe in contact with food.
2. In what order should abrasive paper be used?
- Coarse to fine
- Fine to coarse
- Medium only
- Any order
Show answer
A: Coarse to fine. Each grade removes the scratches of the previous one.
3. What does stain do?
- Protects the wood from water
- Changes the colour of the wood
- Fills holes
- Hardens the surface
Show answer
B: Changes the colour of the wood. It needs a protective finish on top.
4. What is "stopping"?
- Removing tear-out with a scraper
- Sanding the end grain
- Filling small holes and cracks
- Applying the last coat
Show answer
C: Filling small holes and cracks. Not to be confused with scraping.
5. Why rub down between coats of varnish?
- To remove all the varnish and start again
- To change the colour of the finish
- To help the next coat dry much faster
- To give a key and remove dust nibs
Show answer
D: To give a key and remove dust nibs. It gives a smooth surface for the next coat.
Printable worksheet
An I do, we do, you do worksheet for this topic, with a separate answer sheet.