Lesson Notes By Weeks and Term - Junior Secondary 3

Processing of wood - manufactured boards



Class: Junior Secondary School 3

Age: 14 years

Duration: 40 minutes of 5 periods each



Topic: PROCESSING OF WOOD – Manufactured Board

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Define wood defects
  2. Identify common wood defects
  3. Define wood preservation
  4. Identify the methods for applying wood preservatives.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers,

demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,









The teacher explains the meaning of wood defects to the students.

Teacher identify the most common defects

Students pay




Teacher discusses wood preservation and preservatives.

Students pay

attention and





Teacher identify and explain the methods used for applying preservatives.

Students pay

attention and




The teacher writes a summarized

note on the board

The students

copy the note in

their books



PROCESSING OF WOOD –Manufactured Board


Wood defects refer to irregularities, flaws, or abnormalities found in the structure or appearance of wood. These defects can occur naturally during the growth of the tree or result from various processing and environmental factors. Common wood defects include:

  1. Knots: A knot is a portion of a branch or limb embedded in the wood. While small knots may not affect wood quality significantly, large or numerous knots can weaken the wood and impact its structural integrity.
  2. Checks and Splits: Checks are small cracks that develop on the surface of the wood, while splits are larger separations that extend deeper into the wood. These defects often occur during the drying process, especially if it is too rapid.
  3. Warping: Warping includes various deformations in the wood, such as bowing, twisting, cupping, or crooking. These distortions can result from uneven drying, improper storage, or irregularities in the grain.
  4. Burls: Burls are abnormal growths on a tree, resulting in swirling or contorted grain patterns. While burls can create visually appealing wood, they can also lead to irregularities in texture and difficulty in working with the wood.
  5. Insect Damage: Wood-boring insects can create holes, galleries, and tunnels within the wood, affecting its structural integrity. This type of defect is more common in untreated or improperly stored wood.
  6. Sapwood and Heartwood: The contrast between sapwood (newer outer wood) and heartwood (older inner wood) can be considered a defect in some applications, especially if a uniform appearance is desired.


Wood preservation means the process of treating wood with chemicals or any other biochemical substances that can help to prevent or slow down the deterioration of wood caused by either environmental factors or by organisms such as fungi, insects, and wood borers

Preservatives helps to protect wood against attacks of termites, insects and fungi. Examples of wood preservatives includes: Creosote, Pentachlorophenol (PCP): An organochlorine compound, Copper-based Preservatives, Timber Oil etc

Wood preservatives can be applied using various methods to ensure effective penetration and protection. The following are common methods of applying preservatives to wood:

  1. Brushing or Spraying: Preservatives can be applied manually using brushes or sprayers. This method is suitable for smaller wooden items or areas where precision is required. It allows for even coverage and penetration of the preservative.
  2. Dipping: Immersing the wood in a preservative solution is known as dipping. This method is effective for small, individual items like fence posts, where complete coverage is essential. Dipping ensures that the preservative penetrates all surfaces of the wood.
  3. Pressure Treatment: This is a common method for large wood products, such as utility poles and lumber. Wood is placed in a sealed chamber, and preservatives are forced into the wood under high pressure. Pressure treatment ensures deep penetration, providing long-lasting protection.
  4. Soaking: Soaking involves placing wood in a preservative solution for an extended period. This method is suitable for smaller items and provides good penetration of the preservative.
  5. Heat Treatment: Some preservatives are applied in combination with heat treatment. Wood is subjected to high temperatures, allowing the preservatives to penetrate more effectively. Heat treatment is often used for borate-based preservatives.
  6. Surface Coatings: Some wood preservatives come in the form of surface coatings, such as paints, stains, or oils. While these may not penetrate as deeply as other methods, they provide a protective layer on the wood surface.

 EVALUATION: 1. Define wood defects.

  1. Identify 5 common wood defects.
  2. What are preservatives
  3. Mention and discuss 5 methods for applying wood preservatives.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively