Leather footwear production in Kenya plays a vital role in the country's industrial and export sectors, providing employment and contributing significantly to foreign exchange earnings. The construction of high-quality leather shoes requires meticulous preparation of materials to ensure durability, comfort, and aesthetic appeal. This chapter focuses on the essential preparatory processes for construction materials, which form the foundation for successful footwear manufacturing, reflecting the standards expected by both local markets and international buyers.

10.1 Preparation of Construction Materials

The preparation of construction materials involves selecting, conditioning, and processing raw and semi-processed components to meet the design and functional requirements of leather footwear. In Kenya's leather industry, where cow, buffalo, and goat leathers are predominant, understanding the specific properties and treatment of each material is crucial to achieving high-quality shoe uppers, linings, and soles. Proper preparation ensures materials are suitable for assembly, bonding, and finishing processes.

10.1.1 Selection of Leather and Other Materials

Choosing the right materials is the first critical step in footwear construction. Different types of leather and synthetic materials must be evaluated based on their physical properties and intended use in the shoe.

Leather Types Commonly Used in Footwear

• Cowhide Leather: Known for its thickness and durability, cowhide is widely used for shoe uppers due to its strength and ability to withstand wear in everyday use. For instance, many local shoe manufacturers in Nakuru prefer cowhide for making rugged work boots.
• Buffalo Leather: Typically tougher and denser than cowhide, buffalo leather is preferred for soles and heavy-duty footwear. Its bark-tanned variants offer exceptional durability and water resistance.
• Goat Leather: Lightweight and flexible, goat leather is used in formal and casual shoes requiring softness and breathability, such as loafers produced by Nairobi’s artisan shoemakers.
• Split Suede: Derived from the split layer of the hide, suede offers a soft texture and is favored for fashionable and casual footwear, though it requires careful handling during construction due to its delicate surface.
• Synthetic Materials: Various synthetic soles and linings are incorporated to enhance comfort and reduce costs, especially in mid-range footwear targeting local retail markets.

Criteria for Material Selection

• Flexibility and Thickness: Materials must balance flexibility for comfort and thickness for durability. For example, Nairobi-based footwear companies such as Umoja Rubber Products test leather samples to ensure that school shoes can withstand daily wear and tear while remaining comfortable for long walks.
• Tanning Method: Vegetable-tanned leathers are preferred for linings due to their moisture absorption, while chrome-tanned leathers offer colorfastness and softness for uppers. In Eldoret, manufacturers producing shoes for export often select vegetable-tanned linings to meet European Union import standards for natural materials.
• Color and Finish: The aesthetic aspect guides selection, with burnished and polished leathers chosen for formal shoes, while natural finishes suit casual styles. For instance, shoes made for Kenyan banks such as KCB require a high-gloss finish to match corporate dress codes, whereas casual sandals for local markets often use natural, matte leathers.
• Availability and Cost: Local availability of hides influences material choice, affecting production costs and timelines. Small-scale shoemakers in Kisumu may opt for goat leather sourced from local abattoirs to reduce transportation costs and ensure steady supply.
• Environmental Considerations: Increasingly, manufacturers consider eco-friendly tanning and synthetic alternatives to comply with Kenya's environmental regulations, such as those enforced by NEMA. For example, some Nairobi-based factories have shifted to water-based adhesives and vegetable-tanned leathers to appeal to environmentally conscious consumers and meet export requirements.

10.1.2 Conditioning and Pre-Treatment of Leathers

Before assembly, leather materials require conditioning to enhance workability and performance during footwear construction. This phase prepares the leather to withstand mechanical stresses and adhesives used in later processes.

Conditioning Processes for Leather

• Moisture Adjustment: Leather is humidified to restore optimal moisture content, typically around 12-15%, to increase flexibility and prevent cracking during stitching and lasting. In Kenyan factories, this is often done using steam chambers to prepare leather for shoes destined for regions with high humidity, such as Kisumu.
• Softening: Mechanical softening through rolling or staking machines improves pliability, essential for complex shoe designs such as moccasins. For example, artisan workshops in Kariokor, Nairobi, use hand-operated rollers to soften leather for custom-made sandals.
• Edge Trimming and Shaping: Precise cutting and trimming align leather pieces with the shoe pattern, ensuring uniformity and reducing waste. In Nakuru, manufacturers use die-cutting machines to achieve consistent shapes for mass-produced school shoes.
• Surface Cleaning: Removing dust, oils, and residues enhances adhesive bonding and finish quality, a step commonly practiced in leather workshops in Mombasa. This process is critical before applying adhesives to prevent bonding failures in shoes sold in coastal markets.
• Heat Treatment: Controlled heating may be applied to stabilize the leather shape and reduce stress during assembly, particularly for uppers destined for high-end shoes. For instance, some Nairobi export factories use heat guns to pre-shape leather for formal men's shoes, ensuring a crisp, professional appearance.

10.1.3 Preparation of Soles and Insole Materials

Soles and insoles are critical to footwear comfort and durability, requiring specialized preparation to meet performance criteria.

Types and Treatment of Sole Materials

• Leather Soles: Produced predominantly from buffalo hide using bark tanning, these soles are valued for strength and breathability. They are often cut to pattern and conditioned to improve flexibility. Kenyan companies such as Alpha Knits in Thika use locally sourced buffalo leather for premium men's dress shoes, emphasizing traditional craftsmanship.
• Synthetic Soles: Materials such as thermoplastic rubber (TPR) and polyurethane (PU) are prepared by molding or cutting, offering lightweight and wear resistance for casual and sports footwear. In Nairobi, manufacturers producing affordable school shoes for supermarkets often use TPR soles to reduce costs and increase product lifespan.
• Rubber Soles: Prepared through vulcanization, rubber soles provide slip resistance and shock absorption, common in safety shoes used by county government workers. For example, Bata Kenya supplies rubber-soled boots to construction workers in Mombasa, where wet conditions require extra traction.
• Insole Board Preparation: Insoles made from compressed fiberboard or leather are cut and sometimes treated with anti-microbial agents to enhance hygiene within the shoe. Hospitals in Kisii have begun sourcing shoes with treated insoles to reduce foot odor and infections among staff.
• Adhesive Application: Soles and insoles often receive a primer or adhesive layer to improve bonding with other shoe components, an essential step for lasting durability. In export-oriented factories, quality control teams check adhesive application to ensure shoes meet European durability standards.

10.1.4 Preparation and Selection of Adhesives and Bonding Agents

Adhesives play a pivotal role in footwear construction, especially in bonding soles, insoles, and upper components. Selecting and preparing the right adhesive ensures the structural integrity and longevity of the shoe.

Characteristics of Footwear Adhesives

• Type of Adhesive: Common adhesives include contact cement, polyurethane-based adhesives, and synthetic rubber adhesives. Each type has specific bonding strengths and curing times suited to different materials. For example, manufacturers in Nairobi's Industrial Area use polyurethane adhesives for sports shoes to ensure strong bonds that withstand frequent flexing.
• Preparation of Adhesive Surfaces: Surfaces must be clean, dry, and sometimes roughened to maximize adhesion. At a Nairobi shoe factory, leather surfaces are abraded lightly to improve glue penetration, especially for shoes sold in high-traffic retail outlets.
• Application Methods: Adhesives can be applied by brushing, spraying, or roller coating, depending on the production scale and component size. In large factories such as those in Athi River, automated spray systems are used for consistent adhesive application on mass-produced footwear.
• Curing and Drying Times: Proper curing under controlled temperature and pressure is necessary to achieve full bond strength. Some adhesives require heat activation, used in automated assembly lines. For instance, export-oriented factories in Mombasa use heated presses to speed up curing and maintain high output.
• Storage and Handling: Adhesives must be stored in cool, dry conditions to prevent premature curing, with safety measures in place to handle volatile organic compounds (VOCs). Kenyan factories comply with NEMA safety guidelines by providing ventilated storage rooms and training workers on safe handling procedures.

Practice Questions

1. Explain the importance of selecting appropriate leather types for different parts of footwear, citing examples from Kenyan leather industries. (10 marks)
2. Describe the conditioning processes required for leather before footwear assembly and explain why each is necessary. (12 marks)
3. Discuss the preparation of sole materials in leather footwear production and highlight the differences between leather and synthetic soles. (10 marks)
4. Identify key factors to consider when selecting adhesives for footwear construction and explain how these factors influence the bonding process. (8 marks)
   

Chapter Summary

This chapter provides a comprehensive overview of the processes involved in carrying out footwear construction, starting with the preparation of construction materials essential for durable shoe making. It covers the role of bottom fillers, stiffeners, shanks, toe puffs, and insoles, each contributing to the structural integrity and comfort of the footwear. The conditioning of uppers is highlighted as a crucial step to ensure flexibility and proper shaping during the lasting process. Lasting methods are examined in detail, including vertical lasting, flat lasting, and out flanged techniques, which shape the upper around the last to form the shoe. The chapter then explores various footwear construction methods such as direct stuck, moulded, veldtscheon, machine wetted, Californian, and string lasting, explaining their applications and benefits. Finally, it emphasizes the importance of using the correct tools, equipment, and machines to achieve precision and efficiency in shoe production.