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29 finishes

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29 finishes

  1. 1. WOOD MATERIALS TECHNOLOGY 4th Edition
  2. 2. Chapter 29 Finishes
  3. 3. Purpose of a finish  Protects the wood from wear and tear  Prevents decay – fungus, insects  Provides a nice finished surface  Enhances colour  Changes the colour (staining)
  4. 4. Finishing stages Surface preparation Application of finish  Surface preparation – Getting the surfaces smooth and clean – Preparing the piece before putting on the finish  Applying the finish – The steps in putting on the different layers of chosen finish – Different finishes will have slightly different steps
  5. 5. Surface finish  Rub out/remove pencil lines  Scratches and marks can be removed using a scraper  Punch nails and pin below surface  Fill nail holes and small cracks using a suitable wood filler  Sand the surfaces smooth using sandpaper  Sand end grain  Start with 100 grit (medium) sandpaper, then with 180 grit and finally 320 grit (very fine)  Always sand with the grain – avoid scratching the surface  Brush off all dust or use a tack cloth
  6. 6. Sandpaper (glass paper)  Composition of sandpaper – Grit is bonded to the backing paper or card – The grit size is printed on the back of the sandpaper
  7. 7. Types of abrasive
  8. 8. Sanding  Always sand with the grain  Always sand end grain
  9. 9. Paint  Advantages – – – – – – Good inside and outside Lots of colours available Durable Long-lasting Easily-cleaned Covers scratches and defects well  Disadvantages – Hides the beauty of the wood – Difficult to apply well – Needs good preparation – Can blister and peel
  10. 10. Painting wood  Prepare surfaces well  Seal knots with knotting  Apply primer to all surfaces  Fill cracks and holes  Apply 1 – 2 coats of undercoat  Sand lightly  Apply final finish coat  Allow each coat to dry fully
  11. 11. Varnish  Why choose varnish? Water-resistant Scratch-resistant Easily-cleaned Clear finish enhances the grain of the wood – Resists heat – Stains/coloured varnish are available – – – –
  12. 12. Varnish – application  Apply the varnish with a brush/cloth, working with the grain  Cover all surfaces evenly, with no drips/runs  When the first coat is applied, allow to dry  Sand lightly between coats (denib) with very fine sandpaper or fine wire wool  Apply another coat of varnish evenly and leave to dry again  Repeat the process until you have three coats applied
  13. 13. Microporous finishes  Breathable skin  Protect the wood from the weather  Allow moisture to evaporate from the wood  Do not flake or blister  Environmentally friendly  For external use, e.g. sheds/fences
  14. 14. Danish oil  Why choose Danish oil? – Easy to apply – Doesn't raise the grain – Gives a nice shine – Wood can be re-oiled – Suitable for outdoor use
  15. 15. Danish oil – application  Apply with a cloth, work oil well into the grain  Apply two or three coats and leave to dry overnight  De-nib any rough surfaces using light sandpaper  Apply another three coats of oil  Gradually build up the finish using the above process
  16. 16. Wax finishes  Why choose wax? – Easy to apply – Does not raise the grain – Gives nice lustre/shine – Easy to renew – Allows polish to be built up – No sanding between coats – Indoor use only
  17. 17. Wax finishes – application  After surface finishing, seal the wood with a wood sealer  Using a clean dry cloth apply the wax rubbing well into the wood  Build up a number of coats before letting the wax dry for a while  Polish the surface to bring up a shine  Repeat the process to build up to a high gloss shine  Wax is a soft finish and is not water-resistant, so it can only be used indoors
  18. 18. Lacquer  Applied by spraying  Special equipment is required  Proper extraction system is required  Lacquer is harmful if inhaled  Spray gun
  19. 19. Quiz
  20. 20.  Why is it necessary to apply a finish to a wooden artefact? • Seals the wood • Prevents dirt getting in • Enhances the appearance of the piece • Protects the wood from wear and tear
  21. 21.  What is used to clean a brush after applying oil-based paint or varnish? − White spirit
  22. 22.  List the steps required to prepare a wooden item for an applied finish Rub out/remove pencil lines Scratches and marks can be removed using a scraper Punch nails and pins Fill nail holes and small cracks using a suitable wood filler Sand the surfaces smooth using sandpaper Sand end grain Start with 100 grit (medium) sandpaper, then with 180 grit and finally 320 grit (very fine) − Always sand with the grain – avoid scratching the surface − Brush off all dust or use a tack cloth − − − − − − −
  23. 23.  Suggest a finish suitable for a picnic table and give reasons for your choice • Microporous varnish, e.g. Fencelife − Protects the wood − Makes the wood look good − Allows the wood to breathe − Easy to apply − Prevents decay − Does not blister or flake
  24. 24.  Describe the steps in applying varnish to the unit shown − Prepare the surface very well − Apply varnish to the surfaces with a brush or cloth, work with the grain − Cover all surfaces evenly with no drips/runs − When the first coat is applied, allow to dry − Sand lightly between coats with very fine sandpaper or fine wire wool − Apply another coat of varnish evenly and leave to dry again − Repeat the process until you have three coats applied

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