Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Finishing
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Finishing
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Subject: Carpentary And Joinery
Class: Senior Secondary 3
Term: 3rd Term
Week: 4
Theme: Finishes And Finishing
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Prepare surface for application of finishes. Apply finishes by hand and spray gun.
used between coats of finish for optimal smoothness.
Technique:
1. Always sand with the grain of the wood to avoid noticeable scratch marks.
2. Start with a coarse grit (e.g., 80 or 100) if significant smoothing is needed, then progress systematically to medium (120) and finally fine (150-220).
3. Apply even pressure, using a sanding block for flat surfaces to prevent uneven sanding.
4. Between each grit change, thoroughly remove all sanding dust using a brush, vacuum, or tack cloth. Residual coarse grit dust can create scratches when using finer grits.
5. After the final sanding, wipe the surface clean of all dust. Nigerian Context
Example: Sanding a newly planed Ofun (white afara) panel for a cabinet or smoothing a carved statue before staining. 2.
3. Application of Finishes Once the surface is meticulously prepared, the finish can be applied.
Common Finishing Materials in Nigeria: Varnish: A clear, durable finish that protects the wood and enhances its natural grain. It's popular for furniture, doors, and floors. (E.g., Polyurethane varnish, Marine varnish).
Lacquer: A fast-drying, durable clear finish, often used on furniture for a high-gloss or satin look. It offers good resistance to moisture and scratches.
Paint: An opaque finish that covers the wood grain, providing colour and protection. Widely used on utilitarian items, outdoor furniture, or where a specific colour scheme is desired. (E.g., Oil-based enamel, Acrylic paint).
Wood Stain: A transparent or semi-transparent finish that penetrates the wood to add colour while allowing the grain to show through. It's often followed by a clear topcoat (varnish or lacquer).
Wood Polish/Wax: Used for a natural, low-sheen finish or as a top-up protective layer. Often beeswax or carnauba wax based.
Oil Finishes: Penetrating oils (e.g., Danish oil, Teak oil) that soak into the wood, providing a natural look and feel. They offer good protection and are easy to repair. a)
Application by Hand: i. Brushing (for Varnish, Paint, Stain, Lacquer):
1. Preparation: Stir the finish thoroughly (do not shake to avoid bubbles). Ensure the brush is clean and free of loose bristles.
2. Loading the Brush: Dip the brush about halfway into the finish. Tap (do not wipe) excess against the rim of the can.
3. Application: Apply finish in thin, even coats, working with the grain. Use long, overlapping strokes. Avoid overworking or repeatedly brushing an area. For flat surfaces, work from one end to the other. For intricate parts, use a smaller brush. Allow each coat to dry completely according to manufacturer's instructions. Lightly sand (220-400 grit) between coats of varnish/lacquer to remove dust nibs and ensure better adhesion, then wipe clean.
4. Cleaning: Clean brushes immediately after use with the appropriate solvent (mineral spirits for oil-based, water for water-based). Nigerian Context
Example: Varnishing a newly made mahogany dining table or painting a set of wooden kitchen cabinets. ii. Wiping/Rubbing (for Oil Finishes, Wood Stain, Polish/Wax):
1. Preparation: Ensure the surface is dust-free. Use a clean, lint-free cloth (e.g., old cotton t-shirt, cheesecloth).
2. Application: Apply a generous amount of finish (oil, stain) to the cloth. Rub the finish into the wood, working with the grain, ensuring even coverage. Allow the finish to penetrate for the recommended time (e.g., 5-15 minutes for stain, longer for oils). Wipe off all excess finish with a clean, dry cloth. Failure to do so with oil finishes can lead to a sticky residue. For stains, ensure an even colour. For wax/polish, apply a thin coat, let it haze, then buff vigorously with a clean cloth to achieve a sheen.
3. Disposal (Critical for Oil-soaked rags): Rags soaked in oil finishes can spontaneously combust. Always lay them flat to dry completely outdoors, or immerse them in water before disposing of them in a sealed container. Nigerian Context
Example: Applying teak oil to outdoor garden furniture made from local woods or rubbing polish onto a traditional wooden stool. b) Application by Spray Gun (for Lacquer, Varnish, Paint, some Stains): Purpose: Provides a very smooth, even, and professional finish, especially on large surfaces This section details the theoretical and practical aspects of wood finishing, covering surface preparation and application methods. 2.
1. Definition of Finishing Finishing, in carpentry and joinery, refers to the process of applying a protective or decorative coating to a wooden surface.
The primary goals are: Protection: Shielding the wood from moisture, UV radiation, insects, scratches, and general wear and tear.
Enhancement: Improving the aesthetic appeal by highlighting grain patterns, adding colour, or achieving a desired sheen.
Durability: Increasing the lifespan of the wooden product.
Hygiene: Making surfaces easier to clean. 2.
2. Surface Preparation for Finishes Proper surface preparation is fundamental for a high-quality finish. It ensures excellent adhesion of the finish, a smooth final appearance, and uniformity.
The key steps include: a)
Scrapping: Purpose: To remove existing finishes (paint, varnish), glue residue, severe scratches, burrs, and raised grain, resulting in a clean, flat surface. It’s often used as an alternative or precursor to coarse sanding for significant material removal.
Tools: Hand scrapers (cabinet scrapers, pull scrapers), scrapers mounted on planes, or power sanders with coarse grit paper. For hand scrapers, a sharp, burred edge is crucial.
Technique:
1. Hold the scraper at a slight angle (typically 45-60 degrees to the surface).
2. Apply even pressure and push or pull the scraper along the grain of the wood.
3. Work systematically, overlapping strokes slightly.
4. Periodically check the surface for smoothness and evenness.
5. Clean the scraper edge or resharpen as needed. Nigerian Context
Example: Used when renovating old iroko or mahogany furniture found in homes or commercial spaces in Lagos or Ibadan to remove old, peeling varnish. b)
Filling: Purpose: To fill minor defects such as nail holes, screw holes, cracks, knots, dents, and grain pores, creating a uniform and smooth surface before finishing. This ensures a consistent look and prevents the finish from sinking into imperfections.
Materials: Wood Filler: A paste-like material composed of wood dust and a binder. It comes in various colours to match different wood types (e.g., light oak, mahogany). It dries hard and can be sanded, stained, and painted.
Wood Putty: Similar to wood filler but often oil-based and used after the initial finish coat for smaller touch-ups. It remains slightly flexible.
Local Alternatives: Sometimes a mixture of fine sawdust and wood glue can be used for minor repairs, though commercial fillers offer better consistency and durability.
Technique:
1. Ensure the surface is clean and dry.
2. Using a putty knife or spatula, press the filler firmly into the defect, overfilling slightly.
3. Scrape off excess filler immediately, leaving a small mound above the surface.
4. Allow the filler to dry completely according to manufacturer's instructions (usually a few hours to overnight).
5. Once dry, sand the filled area flush with the surrounding wood, working with the grain. Nigerian Context
Example: Filling nail holes on a newly constructed kola wood door frame or cracks in a teak cabinet. c)
Sanding: Purpose: To achieve a smooth, uniform surface texture, remove minor imperfections, and open the wood pores for better finish absorption. Sanding is a progressive process using increasingly finer grits.
Tools: Sandpaper (various grits), sanding blocks, orbital sanders, belt sanders, detail sanders.
Types of Sandpaper (Grits): Coarse (40-80 grit): For initial material removal, shaping, and removing deep scratches or old finishes (after scrapping).
Medium (100-120 grit): For refining the surface after coarse sanding, removing minor imperfections.
Fine (150-220 grit): For final smoothing before applying stains or clear finishes. Higher grits (320-400+) are used between coats of finish for optimal smoothness.
Technique:
1. Always sand with the grain of the wood to avoid noticeable scratch marks.
2. Start with a coarse grit (e.g., 80 or 100) if significant smoothing is needed, then progress systematically to medium (120) and finally fine (150-220).
3. Apply even pressure, using a sanding block for flat surfaces to prevent uneven sanding.
4. Between each grit change, thoroughly remove all sanding dust using a brush, vacuum, or tack cloth. Residual coarse grit dust can create scratches when using finer grits. with a clean cloth to achieve a sheen.
3. Disposal (Critical for Oil-soaked rags): Rags soaked in oil finishes can spontaneously combust. Always lay them flat to dry completely outdoors, or immerse them in water before disposing of them in a sealed container. Nigerian Context
Example: Applying teak oil to outdoor garden furniture made from local woods or rubbing polish onto a traditional wooden stool. b) Application by Spray Gun (for Lacquer, Varnish, Paint, some Stains): Purpose: Provides a very smooth, even, and professional finish, especially on large surfaces or intricate items. It's faster and often yields a better finish than hand application, but requires specialized equipment and skill.
Equipment: Spray Gun: Air spray gun (HVLP - High Volume Low Pressure is common), airless spray gun.
Air Compressor: Provides compressed air for air spray guns. Hoses, Regulators: For connecting and controlling air pressure.
Respirator Mask: Essential for protection against atomized finish particles and fumes.
Ventilation System: Exhaust fans or good natural airflow.
Protective Gear: Gloves, eye protection, overalls.
Safety Precautions: Always work in a well-ventilated area to prevent inhalation of harmful fumes and accumulation of flammable vapours. Wear a NIOSH-approved respirator mask. Wear protective eyewear and gloves. Ensure no open flames or ignition sources are present. Keep a fire extinguisher nearby. Follow manufacturer's guidelines for thinning and handling of finishing materials.
Technique:
1. Preparation: Thin the finish to the manufacturer's recommended viscosity (if necessary). Strain the finish to remove any particles.
2. Gun Setup: Adjust air pressure (for air spray guns) and fluid flow settings on the spray gun. Test spray on scrap material to ensure a good fan pattern and atomization.
3. Application: Hold the spray gun perpendicular to the surface, maintaining a consistent distance (typically 6-10 inches). Move the gun at a steady, even speed. Start spraying off the workpiece, move across, and stop spraying off the workpiece to ensure even coverage at the edges. Overlap each pass by approximately 50% to avoid streaks and ensure uniform film thickness. Apply thin, even coats. Avoid heavy coats that can lead to runs or sags. Allow adequate flash-off time between coats as per manufacturer's instructions. Apply multiple coats as needed for desired build and protection.
4. Cleaning: Clean the spray gun thoroughly immediately after use with the appropriate solvent to prevent clogging and damage. Nigerian Context
Example: Applying lacquer to a large batch of office desks in a furniture factory in Kano or spraying automotive paint onto wooden truck bodies. 3.
1. Teacher Activities: Introduction (10 minutes): The teacher reviews the previous week's topic (e.g., joinery techniques or assembly). The teacher introduces "Finishing" by asking students about the importance of the final appearance and durability of wooden items they encounter daily (e.g., school desks, doors, furniture at home). The teacher states the performance objectives for the lesson. Demonstration and Explanation (30 minutes): The teacher provides prepared wooden offcuts (e.g., a rough plank, one with a nail hole, one with an old finish). The teacher demonstrates scrapping using a hand scraper, explaining the angle and pressure. The teacher demonstrates filling a nail hole or crack with wood filler, showing how to apply, scrape off excess, and explain drying time. The teacher demonstrates sanding using different grits of sandpaper (e.g., 80, 120, 180, 220) with a sanding block, emphasizing sanding with the grain and proper dust removal. The teacher explains and shows samples of common finishing materials (varnish, paint, stain, lacquer). The teacher demonstrates hand application (brushing) of a finish (e.g., water-based varnish or even water to simulate, if actual finish is unavailable). The teacher emphasizes even strokes, working with the grain, and loading the brush. The teacher uses visual aids (charts, diagrams, videos if available) to explain and illustrate spray gun application, focusing on equipment, safety, and technique (distance, overlap, speed).
Guided Discussion and Q&A (15 minutes): The teacher facilitates a discussion on the pros and cons of different finishing materials and application methods. The teacher addresses student questions and clarifies misconceptions.
Practical Activity Setup (5 minutes): The teacher organizes students into small groups and distributes wooden offcuts, sanding papers, and where possible, basic scraping tools and wood filler.
Supervision and Feedback (20 minutes): The teacher circulates among groups, observing student practical work, providing individual guidance, and correcting techniques. The teacher asks probing questions to check understanding (e.g., "Why are you using this grit of sandpaper now?").
Conclusion (5 minutes): The teacher summarizes the key learning points on surface preparation and finish application. The teacher assigns independent practice questions or homework. 3.
2. Student Activities: Active Listening and Observation: Students pay close attention to the teacher's explanations and demonstrations of scrapping, filling, sanding, and finish application.
Participation in Q&A: Students ask questions and contribute to discussions about finishing techniques and materials.
Practical Surface Preparation: In groups, students practice scrapping, filling nail holes/cracks, and progressively sanding wooden offcuts with different grits of sandpaper under teacher supervision.
Simulation of Hand Application: Students simulate applying a finish by hand (e.g., using a brush with water) on a prepared surface, focusing on mastering the technique.
Note-Taking: Students record key concepts, techniques, and safety precautions in their notebooks.
Group Discussion: Students discuss their observations and challenges during practical activities within their groups.
Enhancing Value in Furniture Manufacturing (Economy/Entrepreneurship): Proper finishing directly impacts the market value and perceived quality of locally manufactured furniture. A well-finished table or chair (e.g., an Obeche or Iroko dining set) looks more professional, lasts longer, and commands a higher price in the Nigerian market, whether sold in local craft markets or major furniture stores. This knowledge empowers aspiring carpenters to run profitable businesses. Protection and Longevity in Building Construction (Community/Environment): Wooden components in Nigerian buildings (doors, window frames, roof trusses, ceiling panels made from various timbers like Opepe or Teak) are constantly exposed to harsh tropical conditions (humidity, intense sunlight, insect infestations). Applying appropriate finishes protects these elements from rot, warping, and insect damage, significantly extending their lifespan and reducing the need for frequent repairs or replacements, thereby saving resources and money for homeowners and developers. Preservation of Cultural Heritage and Artistry (Culture/Tourism): Many Nigerian cultural artifacts, traditional musical instruments, and artistic carvings (e.g., Yoruba wooden sculptures, Igbo 'ikenga' figures, Efik mask carvings) are made from wood. Proper finishing techniques are crucial for preserving these invaluable items, protecting them from decay, and enhancing their visual appeal for museums, art galleries, and the tourism industry, both locally and internationally.