Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 2nd Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Wood Work
Curriculum Theme: Vocational Studies
Previous Lesson: Common Timber Preservatives and Their Uses.
Topic: CHARACTERISTICS OF TIMBER PRESERVATIVES AND APPLICATION METHODS
Subject Matter: characteristics of good timber preservative, pressure method, non pressure method

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Identify at least four characteristics of a good timber preservative.
State and explain the two main methods of applying timber preservatives.
Describe specific techniques under pressure and non-pressure methods.

Affective Domain:

Appreciate the importance of preserving timber for durability.
Value the use of safety precautions when handling timber preservatives.

Psychomotor Domain:

Demonstrate the application of timber preservatives using a non-pressure method.
Properly handle instructional materials like hand brushes and gloves during application.

Work collaboratively with peers during practical demonstrations.

Reference Materials

The following resources were used in planning this lesson:

Nigerian Senior Secondary Education Curriculum for Technical and Vocational Education.
State Unified Scheme of Work for Senior Secondary Schools.
Basic Woodwork for Senior Secondary Schools, Book 1.

Instructional Materials

The teacher will teach this lesson with the aid of:

Samples of treated and untreated timber.
Various types of timber preservatives (e.g., creosote, copper-chrome-arsenic).
Hand brush, roller, spray bottle.
Gloves, safety goggles, nose masks.
A small container for dipping.

Rationale for the Lesson

This lesson helps pupils understand how to protect timber from decay and insect attacks, which prolongs its lifespan. Learning about timber preservation enables pupils to make informed choices when working with wood and ensures the durability of their woodworking projects.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of different types of timber, their properties, and common causes of timber degradation.

Lesson Content/Board Summary

CHARACTERISTICS OF TIMBER PRESERVATIVES AND APPLICATION METHODS

Characteristics of a Good Timber Preservative

A good timber preservative is a chemical substance used to protect wood from decay, insects, and other destructive organisms. It should possess the following characteristics:

Toxicity: Must be highly poisonous to wood-destroying fungi and insects.
Permanence: Should remain effective in the timber for a long period without leaching or evaporating.
Penetration: Must be able to penetrate deeply into the wood cells.
Safety: Should be safe for humans, animals, and the environment after application.
Availability: Should be readily available and affordable.
Non-corrosive: Should not corrode metal fasteners used in the timber.
Odour: Should ideally be odourless or have a mild, non-offensive smell.

Methods of Applying Timber Preservatives

There are two main categories for applying timber preservatives to ensure deep penetration and effective protection:

1. Pressure Method

This method involves forcing the preservative into the timber under high pressure inside a closed cylinder. It ensures deep and uniform penetration, making it highly effective for long-term protection.

The following are types of pressure methods:

Full-Cell Process (Bethell Process): The timber is subjected to a vacuum, then the preservative is introduced under high pressure. This process fills the cell cavities of the wood with the preservative, making it suitable for timber used in severe decay conditions (e.g., marine piling).
Empty-Cell Process (Rueping and Lowry Processes): Air is first compressed into the timber, then the preservative is introduced under pressure. When the pressure is released, the compressed air forces out some of the preservative, leaving the cell walls coated but the lumens partially empty. This method uses less preservative while still providing good protection, reducing the weight of the treated timber.

2. Non-Pressure Method

This method involves applying the preservative to the surface of the timber without using external pressure. It provides less penetration compared to the pressure method but is suitable for timber used in less severe conditions or for small-scale applications.

The following are types of non-pressure methods:

Brushing: The preservative is applied directly to the timber surface using a brush. Multiple coats may be required.
Spraying: The preservative is sprayed onto the timber surface using a spray gun. This method is efficient for large surfaces.
Dipping: Timber is briefly immersed in a tank containing the preservative. This provides better penetration than brushing or spraying.
Soaking: Timber is left submerged in the preservative for an extended period (hours or days). This allows for deeper penetration than dipping.
Hot and Cold Open Tank Process: Timber is first soaked in hot preservative, which expands the air in the wood. Then, it is transferred to a cold preservative, causing the air to contract and draw the preservative deep into the wood.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to recall previous lessons on types of timber and common problems affecting wood structures (e.g., decay, insect attacks). The teacher then introduces the topic by explaining the importance of protecting timber.
Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction.
Learning Point: Pupils are reminded of the causes of timber degradation and are prepared for the new topic.

Step 2: Characteristics of Good Timber Preservative

Time: 10 minutes
Teaching Skill: Explanation/Discussion
Teacher’s Activity: The teacher explains what a timber preservative is and discusses the characteristics of a good preservative, writing key points on the board. The teacher uses questions to check for understanding.
Pupils’ Activity: Pupils listen, take notes, and answer questions posed by the teacher.
Learning Point: Pupils understand the qualities of effective timber preservatives.

Step 3: Introduction to Application Methods

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher introduces the two main categories of timber preservative application methods: pressure and non-pressure methods. The teacher explains the basic principle behind each.
Pupils’ Activity: Pupils listen and note the two main categories.
Learning Point: Pupils identify the two broad categories of preservative application.

Step 4: Pressure Method of Application

Time: 7 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the pressure method, detailing the Full-Cell and Empty-Cell processes. The teacher highlights the advantages of this method.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand how preservatives are applied under pressure.

Step 5: Non-Pressure Method of Application

Time: 8 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains and demonstrates various non-pressure methods like brushing, spraying, and dipping using available instructional materials (hand brush, sample timber, gloves). The teacher emphasizes safety precautions.
Pupils’ Activity: Pupils observe the demonstration, ask questions, and practice handling the tools under supervision.
Learning Point: Pupils learn the practical steps for applying preservatives using non-pressure methods and the importance of safety.

Step 6: Comparison of Methods

Time: 5 minutes
Teaching Skill: Comparison/Discussion
Teacher’s Activity: The teacher facilitates a brief discussion comparing the advantages and disadvantages of pressure and non-pressure methods, guiding pupils to understand when each method is appropriate.
Pupils’ Activity: Pupils contribute to the discussion, highlighting differences and suitability of methods.
Learning Point: Pupils can differentiate between the two main application methods and their appropriate uses.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define timber preservative.
List four characteristics of a good timber preservative.
State the two main methods of applying timber preservatives.
Explain briefly the dipping method of preservative application.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 1 minute
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of timber preservation and safe application methods. The teacher assigns homework.
Pupils’ Activity: Pupils listen and note down the homework.
Learning Point: The lesson is reinforced, and pupils are given an opportunity for further practice.

Lesson Keywords

Timber Preservative – Chemical substances used to protect wood from decay and insect attacks.
Pressure Method – A method of applying preservatives by forcing them into timber under high pressure.
Non-Pressure Method – A method of applying preservatives to timber surfaces without external pressure.
Full-Cell Process – A pressure method where timber cell cavities are filled with preservative.
Empty-Cell Process – A pressure method where timber cell walls are coated, but lumens are partially empty.
Brushing – A non-pressure method where preservative is applied with a brush.
Dipping – A non-pressure method where timber is briefly immersed in preservative.

Differentiation

The teacher will provide additional support to struggling learners by pairing them with more advanced pupils for practical activities and offering simplified explanations. Advanced learners will be encouraged to research different types of timber preservatives and their specific applications.

Note for teachers using this lesson plan

Ensure all safety precautions are strictly observed during the demonstration of preservative application. Use appropriate personal protective equipment and ensure good ventilation if working with actual preservatives. Timber samples showing different stages of decay or insect damage can enhance understanding.