Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Wood adhesives
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Wood adhesives
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Wood-Work
Class: Senior Secondary 2
Term: 1st Term
Week: 8
Theme: Design And Construction
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.
Name, classify and state the characteristics and uses of adhesives. Select and prepare adhesives for use. Define gluing terms
use. Forms an extremely strong, rigid, and fully waterproof bond (Type I). Excellent resistance to heat, chemicals, and weathering. Dark, reddish-brown glue line, which can be a disadvantage for light-coloured woods. Requires careful mixing and adequate clamping pressure. Cures at room temperature but faster with heat. More expensive than U
F. Uses: Marine applications (boat building), exterior structural joinery (e.g., laminated beams for bridges or outdoor structures), aircraft components, heavy-duty outdoor furniture.
4. Epoxy Adhesives: Characteristics: Two-part system (resin and hardener) mixed just before use. Forms an incredibly strong, rigid, and waterproof bond. Excellent gap-filling capabilities (can bond imperfectly fitting joints). Bonds a wide variety of materials, including wood, metal, plastic, and ceramics. Chemical resistance. Curing time varies depending on the formulation. Relatively expensive.
Uses: Repairing broken furniture, filling voids, bonding dissimilar materials, marine repairs, specialty woodworking, structural repairs.
5. Rubber-based Adhesives (Contact Cements): Characteristics: Made from synthetic rubber dissolved in solvents or as a water-based emulsion. Applied to both surfaces to be joined, allowed to dry until tacky, then pressed together. Forms an instant, strong bond on contact; no clamping required after initial pressure. Flexible bond. Poor gap-filling properties; requires perfectly mating surfaces. Solvent-based types are highly flammable and have strong fumes; water-based types are safer.
Uses: Laminating plastic decorative laminates (e.g., Formica) to wood surfaces, applying veneers, edge banding, bonding dissimilar flexible materials.
C. Gluing Terms: Understanding these terms is critical for successful adhesive application.
1. Open Time: The maximum time allowed between applying the adhesive to the wood surface and bringing the two surfaces together to form a joint. If the surfaces are joined after the open time, a weak bond will result.
2. Closed Time (or Assembly Time): The time elapsed from when the two adhesive-coated surfaces are brought together until clamping pressure is applied. This is often part of the open time.
3. Clamping Time: The minimum period during which the joint must be held under pressure (clamped) to allow the adhesive to cure sufficiently to hold the joint without slipping. Removing clamps too early can result in a weak or failed joint.
4. Cure Time: The total time required for the adhesive to fully harden and develop its maximum strength. This often extends beyond clamping time.
5. Pot Life: The duration for which a mixed multi-component adhesive (e.g., epoxy, UF, RF) remains usable after mixing before it starts to thicken or harden too much to be applied effectively.
6. Spread Rate: The amount of adhesive applied per unit area of the joint surface. Proper spread rate is crucial; too little leads to starved joints, too much can lead to squeeze-out and weakened bonds.
7. Squeeze-out: Excess adhesive that oozes out from the joint line when clamping pressure is applied. A slight squeeze-out indicates sufficient adhesive application.
8. Starved Joint: A joint that lacks sufficient adhesive, resulting in a weak bond. This occurs due to inadequate spread rate or excessive clamping pressure forcing too much adhesive out.
9. Glue Line: The thin layer of cured adhesive visible between the two joined wood surfaces.
1
0. Tack: The initial stickiness of an adhesive before it fully cures, allowing surfaces to hold together momentarily.
Selecting and Preparing Adhesives for Use: Selection Criteria: Application: Interior (PVA, animal glue) or Exterior (RF, epoxy, waterproof PVA).
Required Strength: High (RF, epoxy), Moderate (PVA, UF), Low (starch).
Moisture Resistance: Waterproof (RF, epoxy), Water-resistant (UF, casein, waterproof PVA), Low (animal glue, standard PVA).
Gap-filling Ability: Excellent (Epoxy), Moderate (some UF), Poor (Contact Cement).
Setting Time/Assembly Time: Fast (PVA, contact cement), Slow (animal glue, some epoxies).
Cost: Inexpensive (PVA), Moderate (UF, casein), Expensive (RF, epoxy).
Colour of Glue Line: Clear/light (PVA, UF), Dark (RF, casein on some woods).
Toxicity/Safety: Low (PVA), Requires ventilation (UF, RF, solvent-based contact cement).
Preparation for Common Adhesives:
1. PVA Glue: Shake well before use. Apply directly from the bottle or using a brush/roller. Ensure surfaces are clean and free of dust. No mixing required. 2. *Animal (Epoxy), Moderate (some UF), Poor (Contact Cement).
Setting Time/Assembly Time: Fast (PVA, contact cement), Slow (animal glue, some epoxies).
Cost: Inexpensive (PVA), Moderate (UF, casein), Expensive (RF, epoxy).
Colour of Glue Line: Clear/light (PVA, UF), Dark (RF, casein on some woods).
Toxicity/Safety: Low (PVA), Requires ventilation (UF, RF, solvent-based contact cement).
Preparation for Common Adhesives:
1. PVA Glue: Shake well before use. Apply directly from the bottle or using a brush/roller. Ensure surfaces are clean and free of dust. No mixing required.
2. Animal Glue: Break solid glue into smaller pieces or use granules/flakes. Soak in cold water for a few hours (e.g., 1 part glue to 1-2 parts water by weight). Heat in a double boiler (or glue pot) until fully liquid and smooth (never boil). Maintain temperature during use.
3. Casein Glue: Mix powdered glue with the recommended amount of cold water, slowly stirring to avoid lumps. Allow to stand for 10-15 minutes, then stir again. Use within its pot life (typically 4-8 hours).
4. Urea-Formaldehyde (UF)
Glue (Powdered Type): Mix powdered resin with the recommended amount of water, stirring thoroughly until smooth. Some formulations require a separate catalyst to be added later or are pre-catalyzed. Use immediately within its pot life. Ensure good ventilation.
5. Resorcinol Formaldehyde (RF)
Glue: Carefully measure and mix the liquid resin and powdered hardener (catalyst) in the exact proportions specified by the manufacturer. Stir thoroughly until a uniform mixture is achieved. Use immediately within its short pot life. Wear gloves and ensure excellent ventilation due to strong fumes and potential skin irritation.
6. Epoxy Adhesives: Measure out equal (or specified) parts of resin and hardener onto a clean, non-absorbent surface (e.g., cardboard, plastic tray). Mix thoroughly for 1-2 minutes until uniformly blended and no streaks are visible. Use immediately within its pot life. Wear gloves.
7. Contact Cement: Ensure surfaces are clean and dry. Apply a thin, even coat to both surfaces using a brush, roller, or spreader. Allow both surfaces to dry completely until tacky to the touch (usually 15-30 minutes, check manufacturer's instructions). Carefully align the surfaces, as bonding is instant on contact. Apply firm, even pressure over the entire area (e.g., with a roller or block).
Safety Precautions for Handling Adhesives: Always read and follow the manufacturer's instructions and safety data sheets (SDS). Work in a well-ventilated area, especially with solvent-based or formaldehyde-releasing adhesives (UF, RF, contact cement). Wear appropriate personal protective equipment (PPE): gloves, safety glasses, and sometimes a respirator. Avoid skin and eye contact. Wash hands thoroughly after use. Store adhesives properly in their original containers, away from heat, direct sunlight, and out of reach of children. Dispose of waste materials according to local regulations. This section provides in-depth explanations of wood adhesives, their classifications, characteristics, uses, and relevant terminology.
Definition of Adhesives: Adhesives are non-metallic substances applied to the surfaces of materials (adherends) that can bind them together and resist separation. In woodworking, they create a strong, durable bond between pieces of wood, often stronger than the wood itself.
Classification of Adhesives: Wood adhesives can be broadly classified based on their origin (natural or synthetic) or their setting mechanism.
A. Natural Adhesives: These are derived from organic sources. They are generally less water-resistant and have lower strength compared to many synthetic adhesives but are often reversible and less toxic.
1. Animal Glue (e.g., Hide Glue, Bone Glue): Characteristics: Made from collagen found in animal hides, bones, and tissues. Supplied in dry granular, flake, or cake form, requiring heating and mixing with water before use. Thermoplastic (becomes liquid when heated, solidifies when cooled), allowing for reversible joints. Excellent strength for joints that are not exposed to moisture. Has a long "open time" (time before it starts to set), making it suitable for complex assemblies. Relatively poor resistance to moisture and fungal attack. Odorous when heated.
Uses: Traditional fine furniture making, antique restoration (due to reversibility), veneer application, musical instrument construction.
2. Casein Glue: Characteristics: Derived from milk proteins (casein). Supplied as a powder, mixed with water and an alkali (e.g., lime) to activate. Strong, rigid bond. Good moisture resistance, making it suitable for moderately damp conditions (better than animal glue, but not fully waterproof). Alkaline nature can stain some woods (e.g., oak, mahogany) a dark colour. Has a relatively short pot life once mixed. Can be abrasive to cutting tools.
Uses: Boat building (early forms), exterior joinery (where high moisture resistance is not paramount), laminating curved members, general woodworking.
3. Starch/Dextrin Glues: Characteristics: Derived from plant starches (e.g., maize, cassava). Easy to prepare and apply. Relatively low strength and poor water resistance. Inexpensive.
Uses: Primarily for paper, cardboard, and light-duty wood applications, less common for structural wood joints.
B. Synthetic Adhesives: These are chemically manufactured polymers, offering a wide range of properties, often superior in strength, water resistance, and durability.
1. Polyvinyl Acetate (PVA) Glue (White Glue, Carpenter's Glue): Characteristics: Water-based emulsion, milky white when liquid, dries clear or translucent. Very common, versatile, and easy to use. Non-toxic (when dry), low odour. Good initial tack and reasonably fast setting time. Strong bond, generally stronger than wood itself.
Available in different formulations: standard (interior use), water-resistant (Type II, for exterior but covered applications), and waterproof (Type I, for full exterior exposure). Creeps under sustained load over time (not ideal for structural applications where constant stress is present).
Uses: General woodworking, furniture assembly (chairs, tables), edge gluing, laminating, craft projects. Widely used in school workshops and home carpentry.
2. Urea-Formaldehyde (UF)
Resin Glue: Characteristics: Supplied as a powder (mix with water) or a two-part liquid system (resin and hardener/catalyst). Forms a rigid, strong, and durable thermosetting bond (does not soften with heat once cured). Good water resistance when properly catalyzed. Requires clamping pressure and curing time (influenced by temperature). Can release formaldehyde fumes during curing, requiring good ventilation. Glue line is typically light in colour.
Uses: Plywood and particleboard manufacturing, laminating, veneering, furniture components, general joinery requiring good water resistance.
3. Resorcinol Formaldehyde (RF)
Resin Glue: Characteristics: Two-part system (resin and hardener/catalyst) mixed before use. Forms an extremely strong, rigid, and fully waterproof bond (Type I). Excellent resistance to heat, chemicals, and weathering. Dark, reddish-brown glue line, which can be a disadvantage for light-coloured woods. Requires careful mixing and adequate clamping pressure. Cures at room temperature but faster with heat. More expensive than U
F. Uses: Marine applications (boat building), exterior structural joinery (e.g., laminated beams for bridges or outdoor structures), aircraft components, heavy-duty outdoor furniture.
4. Epoxy Adhesives: Characteristics: Two-part system (resin and hardener) mixed just before This section outlines practical, teacher-led and student-centred activities for delivering the lesson.
Teacher Activities: Introduction & Hook (10 mins): Begin by displaying various wooden joints (e.g., mortise and tenon, dovetail, butt joint) and asking students how they are held together without nails or screws. Introduce the concept of adhesives as critical bonding agents in woodworking. Briefly state the learning objectives for the lesson.
Explanation of Key Concepts (25 mins): Define "adhesive" and explain its function. Present the classification of adhesives (Natural vs. Synthetic). For each adhesive type (Animal Glue, Casein, PVA, UF, RF, Epoxy, Contact Cement): Describe its characteristics using clear language. State its common uses with Nigerian-relevant examples (e.g., furniture making in Nnewi, boat building in Niger Delta, laminating Formica for kitchen cabinets).
Show visual aids: actual adhesive containers, samples of cured glue lines, or images/videos of their application. Explain the "gluing terms" (open time, clamping time, starved joint, etc.) using simple diagrams or analogies. Demonstration of Adhesive Selection and Preparation (20 mins): Simulated Scenario: Present a scenario, e.g., "A customer wants a durable outdoor garden bench." Guide students through selecting the appropriate adhesive (e.g., RF or waterproof epoxy) based on requirements. Practical Demonstration (if resources allow): Demonstrate the preparation of 2-3 different types of adhesives (e.g., mixing a powdered UF glue with water, measuring and mixing epoxy, showing how to heat animal glue). Emphasize proper measurement and safety. Demonstrate the application technique for PVA glue on a simple butt joint and show how to apply contact cement on a small piece of laminate. Highlight safety precautions (ventilation, gloves, eye protection).
Facilitate Discussion and Q&A (10 mins): Encourage students to ask questions about the different adhesives. Ask probing questions to check understanding (e.g., "Why would you not use animal glue for an outdoor project?").
Student Activities: Note-Taking and Active Listening (Throughout): Students will actively listen, observe demonstrations, and take detailed notes on adhesive types, characteristics, uses, and terminology. Observation and Engagement (Demonstration Phase): Students will carefully observe the teacher's demonstration of adhesive preparation and application, asking clarifying questions. Small Group Discussion/Brainstorm (15 mins): Divide students into small groups. Provide each group with a hypothetical woodworking project scenario (e.g., "Building a school desk for indoor use," "Repairing a broken wooden canoe," "Attaching veneer to a plywood cabinet"). Each group discusses and selects the most appropriate adhesive, justifying their choice based on characteristics and uses learned. They also identify potential safety considerations.
Report Back/Peer Learning (5 mins): Each group briefly presents their chosen adhesive and rationale to the class. Other groups provide feedback or alternative suggestions.
Materials and Resources: Whiteboard/Chalkboard and markers/chalk Projector (optional) for images/videos Samples of different wood adhesives (actual containers: PVA, UF powder, epoxy kit, contact cement, animal glue flakes if available). Samples of wood joints (e.g., butt joint, lap joint, dowel joint) Mixing cups, stirring sticks, brushes, spatulas for demonstration Personal Protective Equipment (PPE) for teacher demonstration: gloves, safety glasses. Small wood offcuts for application demonstration. Plastic laminate/veneer samples for contact cement demo. Handouts with key definitions and adhesive classifications (optional).
Local Furniture Industry Enhancement: In Nigeria, the furniture industry (e.g., in Aba, Lagos, Kano) heavily relies on wood joints. Students can apply their knowledge to select optimal adhesives for specific furniture types. For example, using water-resistant PVA for everyday household furniture to withstand humid conditions, or more robust UF/Epoxy for outdoor market stalls or robust school furniture, thereby increasing product durability and market value for local artisans. Building and Construction in Challenging Environments: Nigeria has diverse climatic zones, including high humidity coastal regions and drier northern areas. Knowledge of waterproof adhesives (like RF or marine-grade epoxy) is critical for constructing wooden structures (e.g., boat repairs in riverine communities, wooden bridges, roofing elements) that can withstand environmental stressors, contributing to safer and longer-lasting infrastructure.
DIY and Entrepreneurship in Repairs: Many Nigerian households and small businesses face the challenge of repairing broken wooden items (furniture, tools, crafts) rather than replacing them due to cost. Students can use their understanding of gap-filling epoxy for complex breaks or strong PVA for simple joinery repairs, fostering a culture of maintenance, reducing waste, and even developing small repair businesses within their communities.