Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Abrassives
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Abrassives
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Carpentary And Joinery
Class: Senior Secondary 1
Term: 3rd Term
Week: 9
Theme: Finishes And Finishing
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Mention abrading to ols. List types of abrasive and uses. Identify grades of abrasives. Make choice of grade for application and use.
grits. This is known as progressive sanding. Do not skip grits (e.g., jumping from 60 grit directly to 220 grit) as the coarser scratches will not be fully removed by the much finer grit, leading to a visible 'ghost' of the previous scratches after finishing.
A typical progression might be: 80 -> 120 -> 150 -> 180 ->
2
2
0. Factors Influencing Choice:
1. Initial Condition of the Wood: Very Rough/Heavily Painted: Start with coarse grit (40-80).
Rough but Planed: Start with medium grit (100-120). Already Smooth (e.g., between finish coats): Start with fine grit (180-220 or higher).
2. Type of Wood: Hardwoods (Iroko, Mahogany, Teak): Generally require more aggressive sanding initially. Aluminium Oxide is excellent. Softwoods (Obeche, Pine): Can clog sandpaper easily. Silicon Carbide or less aggressive Aluminium Oxide may be preferred.
3. Desired Final Finish: Rough, rustic look: May only require medium grit (100-120). Smooth, ready for paint/stain: Requires fine grit (180-220). Polished, mirror-like finish: Requires very fine to super fine grits (320+).
4. Type of Finish Being Applied: Oil finishes: May not require as fine a sanding as film-building finishes.
Water-based finishes: Can raise wood grain, requiring additional light sanding after the first coat.
Lacquer/Varnish: Often requires very fine sanding between coats to achieve a smooth, even film. Practical
Examples: Scenario 1: Refurbishing an old, heavily painted wooden window frame.
Choice: Start with a 60-grit Aluminium Oxide sandpaper on a belt sander (for flat sections) or orbital sander to aggressively remove old paint. Then progress to 100-grit, 150-grit, and finally 180-grit for a smooth surface ready for new paint.
Scenario 2: Preparing a newly constructed Sapele (hardwood) table top for varnish.
Choice: Begin with 100-grit Garnet or Aluminium Oxide to remove machine marks. Follow with 120-grit, then 150-grit, then 180-grit, and finally 220-grit. After the first coat of varnish, light sand with 320-grit Silicon Carbide (wet or dry) before subsequent coats.
Scenario 3: Smoothing the carved legs of a wooden stool made from Obeche (softwood).
Choice:* Use a sanding sponge with 120-grit Silicon Carbide for initial shaping and smoothing. Progress to 180-grit, then 220-grit for a smooth finish suitable for painting or staining. The flexibility of the sponge helps with contours. for general wood finishing.
Pumice: A lightweight, porous volcanic rock. Crushed to produce a very fine abrasive powder. Used for polishing wood finishes to achieve a high sheen.
Synthetic/Manufactured Abrasives: Engineered for specific properties, offering superior performance and consistency.
Aluminium Oxide (AlO2): (Most common for woodworking) - Brown or reddish-brown. Very durable, tough, and fractures to expose new sharp edges. Excellent all-rounder for general sanding of wood, especially hardwoods (e.g., Iroko, Mahogany). Good for removing material quickly and for final sanding. Application
Example: Sanding down a newly planed Teak dining table, from rough shaping to fine finishing.
Silicon Carbide (SiC): Black, very hard and sharp but more brittle than aluminium oxide. Its sharp, brittle crystals break down quickly, producing a very fine finish. Excellent for softwoods (e.g., Obeche, Pine), painted surfaces, plastics, and wet sanding (where it's used with water to prevent clogging and reduce dust). Application
Example: Wet sanding a painted wooden door frame to achieve a smooth finish before the final coat of paint, or sanding between coats of varnish on a Sapele wood surface.
Zirconia Alumina: (Zirconia or Zircon) - Greenish-blue. An alloy of aluminium oxide and zirconium oxide. Extremely tough and durable, self-sharpening. Used for aggressive stock removal on very hard woods, composites, and metals. Excellent for power sanders due to its resistance to heat and wear. Application
Example: Heavy-duty sanding of very hard woods or removing tough old finishes with a belt sander.
Ceramic Abrasives: Reddish-brown. Engineered for extreme durability and self-sharpening characteristics. Used in heavy-duty industrial applications for grinding and very aggressive sanding, especially with power tools like belt sanders. Application
Example: Industrial sanding of large timber slabs or composite panels. 2.
4. Grades of Abrasives (Grit Size) (Performance Objective 3) The "grade" or "grit" of an abrasive refers to the size of its abrasive particles. Grit numbers are inversely proportional to particle size: Lower Grit Number = Coarser Abrasive (larger particles, more aggressive cutting) Higher Grit Number = Finer Abrasive (smaller particles, smoother finish) Abrasive grades are typically categorized as follows: Coarse Grit (e.g., 40-80 grit): Appearance: Particles are visibly large and rough to the touch.
Use: For aggressive material removal, stripping old paint/varnish, initial shaping, or sanding extremely rough or heavily damaged wood surfaces. Removes material quickly but leaves a very rough finish. Medium Grit (e.g., 100-150 grit): Appearance: Particles are smaller, less rough than coarse.
Use: For general sanding, smoothing slightly rough surfaces, removing minor imperfections, and preparing surfaces after coarse sanding, before moving to finer grits. Fine Grit (e.g., 180-220 grit): Appearance: Particles are fine, the surface feels smooth with a slight texture.
Use: For final sanding before applying stain, paint, or varnish. Used to achieve a smooth, ready-to-finish surface. Also suitable for light sanding between coats of finish. Very Fine Grit (e.g., 240-320 grit): Appearance: Very smooth, almost no discernible texture.
Use: For ultra-smooth finishes, light sanding between multiple finish coats (especially lacquer or varnish), and for preparing wood for polishing. Extra Fine/Super Fine Grit (e.g., 360+ grit): Appearance: Extremely smooth, almost like paper.
Use: Primarily for polishing wood surfaces and finishes to achieve a high sheen or mirror-like appearance. 2.
5. Making Choice of Grade for Application and Use (Performance Objective 4) Selecting the correct abrasive type and grit is crucial for efficiency, achieving the desired finish, and preventing damage to the workpiece.
General Rule for Sanding: Always start with a coarse grit to remove major imperfections and then progressively move to finer grits. This is known as progressive sanding. Do not skip grits (e.g., jumping from 60 grit directly to 220 grit) as the coarser scratches will not be fully removed by the much finer grit, leading to a visible 'ghost' of the previous scratches after finishing.
A typical progression might be: 80 -> 120 -> 150 -> 180 ->
2
2
0. Factors Influencing Choice:
1. Initial Condition of the Wood: Very Rough/Heavily Painted: Start with coarse grit (40-80).
Rough but Planed: Start with medium grit (100-120). *Already Smooth (e.g., between finish This section provides in-depth explanations of the core concepts related to abrasives in carpentry and joinery. 2.
1. Definition of Abrasives Abrasives are hard, granular materials used to grind, sand, rub, or polish another material to remove a small amount of material, create a smooth surface, or impart a specific texture. In carpentry, they are primarily used to prepare wood surfaces for finishing (e.g., painting, varnishing, staining) or to achieve a desired smoothness. Why are abrasives essential in carpentry?
Surface Preparation: To remove saw marks, planer marks, and other imperfections from wood.
Finish Adhesion: To create a 'tooth' or texture on the wood surface, allowing paints, varnishes, and stains to adhere better.
Old Finish Removal: To strip old paint, varnish, or lacquer before applying a new finish.
Shaping and Contouring: To refine shapes and curves where cutting tools cannot provide the necessary precision.
Between-Coat Sanding: To smooth raised grain and previous finish coats, ensuring subsequent coats lay down smoothly. 2.
2. Abrading Tools (Performance Objective 1) Abrading tools are devices that hold or utilize abrasive materials to perform sanding or grinding operations. They can be broadly categorized into hand tools and power tools.
Hand Abrading Tools: Sandpaper (used by hand): The most basic form, where a sheet of sandpaper is held directly in the hand and rubbed against the workpiece. Best for small, intricate areas or light touch-ups.
Sanding Block: A block of wood, cork, rubber, or plastic around which sandpaper is wrapped. It provides a flat, firm backing, ensuring even pressure distribution and preventing 'finger marks' or uneven sanding. Essential for achieving flat surfaces.
Sanding Sponges/Pads: Abrasive material bonded to a foam sponge. Flexible, allowing them to conform to curved or contoured surfaces. Often washable and reusable.
Power Abrading Tools (Sanders): These tools use electric motors to rapidly move or rotate abrasive sheets/discs, significantly increasing efficiency.
Orbital Sander: Uses a rectangular abrasive sheet that moves in small orbits. Good for general-purpose sanding, especially on flat surfaces. Leaves a swirl pattern that might be visible if not followed by finer sanding.
Random Orbital Sander: Uses a circular abrasive disc that both spins and moves in small, random orbits. This random action reduces visible swirl marks, making it excellent for achieving a finer finish. Versatile for general sanding.
Belt Sander: Uses a continuous loop of abrasive material (a belt) that rotates at high speed. Designed for aggressive material removal on large, flat surfaces. Excellent for initial rough sanding or leveling.
Detail Sander (Mouse Sander): Small, triangular base, designed for sanding in tight corners, intricate details, and small areas where larger sanders cannot reach.
Disc Sander: Uses a circular abrasive disc that rotates. Often part of a bench-mounted machine, used for shaping and sanding edges. 2.
3. Types of Abrasives and Uses (Performance Objective 2) Abrasives are made from various natural and synthetic materials, each with distinct properties suited for different applications.
Natural Abrasives: Derived directly from minerals found in nature.
Flint: (Also known as 'glass paper') - Greyish-white, relatively soft and dull, wears quickly. Historically used but largely replaced by modern abrasives. Inefficient for contemporary woodworking.
Garnet: Reddish-brown, durable, sharp, and fractures to create new cutting edges. Excellent for general woodworking, especially for achieving a smooth finish on hardwoods and softwoods. It leaves a nice finish, making it popular for furniture.
Emery: Black, a mixture of corundum and magnetite. Very tough and durable, often used for metal sanding (e.g., sharpening tools) but can be used for very heavy-duty wood sanding or removing rust. Less common for general wood finishing.
Pumice: A lightweight, porous volcanic rock. Crushed to produce a very fine abrasive powder. Used for polishing wood finishes to achieve a high sheen.
Synthetic/Manufactured Abrasives: Engineered for specific properties, offering superior performance and consistency.
Aluminium Oxide (AlO2): (Most common for woodworking) - Brown or reddish-brown. Very durable, tough, and fractures to expose new sharp edges. Excellent all-rounder for general sanding of wood, especially hardwoods (e.g., Iroko, Mahogany). Good for removing material quickly and for final sanding. Application
Example:* Sanding down a newly planed This section outlines practical and engaging activities for effective lesson delivery in a typical Nigerian classroom. 3.
1. Introduction (10 minutes)
Teacher Activity: Teacher displays various samples of sandpaper (different grits, types) and a few abrading tools (e.g., sanding block, an old piece of sandpaper, if possible a small orbital sander). Teacher picks up a rough piece of wood and then a smooth, finished piece.
Student Activity: Students observe the samples and tools. Teacher asks students if they have ever used sandpaper or seen someone sanding wood. Students share their experiences or observations, discussing why wood needs to be smoothed. 3.
2. Activity 1: Identifying Abrading Tools (15 minutes)
Teacher Activity: Teacher presents pictures or actual examples of various hand and power abrading tools (sanding block, sanding sponge, sandpaper sheet, orbital sander, belt sander, detail sander). For each tool, the teacher briefly explains its basic function.
Student Activity: Students identify the tools displayed. In groups, students discuss where they might have seen these tools used in their communities (e.g., furniture workshops, construction sites, mechanic shops). Students list at least three hand and two power abrading tools in their notebooks. 3.
3. Activity 2: Exploring Types of Abrasives (20 minutes)
Teacher Activity: Teacher explains the difference between natural and synthetic abrasives. Teacher provides students with small labeled samples of different sandpaper types (e.g., Aluminium Oxide, Silicon Carbide, Garnet) if available, or clear pictures showing their characteristic colours and textures. Teacher explains the typical uses for each.
Student Activity: Students examine the samples (or pictures). They feel the texture and observe the colour differences. Students note down the key characteristics and typical uses of at least two natural and two synthetic abrasive types, linking them to local wood types where applicable (e.g., Aluminium Oxide for Iroko, Silicon Carbide for Obeche). 3.
4. Activity 3: Understanding Grades of Abrasives (20 minutes)
Teacher Activity: Teacher demonstrates how to identify the grit number on sandpaper. Teacher arranges several sandpaper samples (e.g., 60, 120, 180, 220, 320 grit) in order on a board. Teacher explains the concept of coarse vs. fine grit and how the number indicates particle size and aggressiveness.
Student Activity: Students handle the sandpaper samples, feeling the difference in texture. They practice identifying the grit number. In pairs, students describe the feel and visual difference between a 'coarse' (e.g., 80-grit) and a 'fine' (e.g., 220-grit) sandpaper. 3.
5. Activity 4: Choosing the Right Grade for Application (25 minutes)
Teacher Activity: Teacher presents three different small wooden pieces: A very rough piece (e.g., freshly cut plank with saw marks). A piece with some minor imperfections or old paint. A relatively smooth piece needing final preparation for varnish. Teacher provides various grits of sandpaper (e.g., 60, 120, 180, 220). Teacher demonstrates the concept of progressive sanding on one piece.
Student Activity: In small groups, students are given a wood sample and a selection of sandpaper grits. They discuss and select the appropriate starting grit and the progression of grits needed to achieve a smooth, finish-ready surface for their assigned wood piece. Groups then demonstrate their chosen sanding progression on their wood sample (if materials allow, or verbally explain the steps if limited). 3.
6. Conclusion and Discussion (5 minutes)
Teacher Activity: Teacher summarises the importance of abrasives in achieving quality finishes and solicits questions.
Student Activity: Students ask clarifying questions and reinforce their understanding through a brief class discussion on the benefits of proper abrasive selection.
This topic has strong practical relevance in various Nigerian contexts, integrating with community, economy, and culture. Furniture Manufacturing and Craftsmanship (Economy & Culture): Abrasives are indispensable in the thriving Nigerian furniture industry, from small-scale roadside workshops to large factories. Skilled application of abrasives ensures the smooth, attractive finishes seen on furniture sold in markets like those in Lagos, Aba, and Kano. Local artisans who carve traditional statues, drums, or decorative panels also rely on precise abrasive use for detailed finishing, enhancing the aesthetic and market value of their craft. This directly impacts the livelihoods of many Nigerians involved in woodworking. Building Construction and Renovation (Community & Economy): In urban and rural construction projects across Nigeria, carpenters use abrasives to prepare wooden components like doors, window frames, skirting boards, and ceiling panels. Proper sanding ensures these elements are smooth, easy to paint or varnish, and durable. For instance, when renovating old colonial-era buildings in Calabar or Lagos, removing old finishes from sturdy hardwood doors requires a good understanding of abrasive types and grades. Automotive Refinishing and Repair (Economy): While primarily for metal, the principles of abrasive use are directly transferable to the widespread car body repair and painting industry in Nigeria, often found in 'Ladipo-style' markets. Technicians use various grits of sandpaper to strip old paint, smooth out body filler, and prepare car panels for new paint jobs, ensuring a smooth and professional finish. This provides employment and critical services within the transport sector.