WOOD MATERIALS TECHNOLOGY 4 th Edition

Chapter 29 Finishes

Protects the wood from wear and tear Prevents decay – fungus, insects Provides a nice finished surface Enhances colour Changes the colour (staining) Purpose of a 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 Surface preparation Application of finish Finishing stages

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 Surface finish

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

Types of abrasive

Always sand with the grain Always sand end grain Sanding

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 Paint

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 Painting wood

Why choose varnish? – Water-resistant – Scratch-resistant – Easily-cleaned – Clear finish enhances the grain of the wood – Resists heat – Stains/coloured varnish are available Varnish

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 Varnish – application

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

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

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

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

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

Lacquer Applied by spraying Special equipment is required Proper extraction system is required Lacquer is harmful if inhaled Spray gun

Quiz

Seals the wood Prevents dirt getting in Enhances the appearance of the piece Protects the wood from wear and tear Why is it necessary to apply a finish to a wooden artefact?

− White spirit What is used to clean a brush after applying oil-based paint or varnish?

− 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 List the steps required to prepare a wooden item for an applied finish

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 Suggest a finish suitable for a picnic table and give reasons for your choice

− 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 Describe the steps in applying varnish to the unit shown