Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Explain the process of building walls up to Damp-Proof Course (DPC) level.
• Describe the importance and installation of DPC and Damp-Proof Membranes (DPM).
• Differentiate between various types of floor finishes and their uses.

Lesson summary

This week, we delve deeper into the construction processes involved in superstructures and finishes. Superstructures form the above-ground part of a building, providing shelter and support, while finishes are the final touches that determine the aesthetic appeal and functionality of the building’s interior and exterior. Understanding these processes is crucial for a Civil Technologist, as it equips you with the knowledge to effectively plan, manage, and execute construction projects. In South Africa, with its diverse climate and growing infrastructure needs, a strong understanding of these concepts is essential for creating sustainable, durable, and aesthetically pleasing buildings.

Lesson notes

2.1 Building Walls Up to DPC Level The foundation is the base upon which the entire structure rests. Correct setting out is critical.

Setting Out: This involves accurately transferring the building plan dimensions from the drawing onto the ground. This usually uses pegs, strings, and a theodolite or builder's square. Ensure right angles are accurately set using the 3-4-5 method (Pythagorean theorem). If the sides of a triangle are 3m, 4m, and 5m, the angle between the 3m and 4m sides is a right angle.

Foundation Preparation: This involves excavating the soil to the required depth and width according to the engineer's specifications. The bottom of the excavation should be level and compacted to provide a stable base. In expansive clay soils common in parts of South Africa, special foundation techniques like reinforced concrete rafts or piled foundations might be necessary to prevent cracking.

Laying the Foundation: A concrete foundation is typically poured. This provides a level and stable base for the walls. Ensure adequate compaction of the concrete to remove air pockets and increase its strength. Follow SANS 10100-2 for concrete mix design.

Brick/Block Laying: Bricks or blocks are laid in courses, bonded together with mortar. Common bond patterns include stretcher bond (simplest, used for single-skin walls), English bond (strongest, alternating courses of headers and stretchers), and Flemish bond (alternating headers and stretchers in each course). Vertical joints should be staggered to provide strength.

Mortar Mix Ratios: A typical mortar mix is 1:1:6 (cement:lime:sand) or 1:3 (cement:sand) depending on the required strength and workability. Lime improves workability and water retention. Too much cement can lead to cracking.

Damp-Proof Course (DPC): This is a waterproof barrier installed in the wall, usually just above ground level. It prevents rising damp, where moisture from the ground is drawn up into the wall by capillary action. Materials used for DPC include bitumen felt, plastic, or slate. It's crucial the DPC forms a continuous barrier.

Example: Imagine building a small 4m x 6m single-story house in Gauteng. You would first set out the perimeter using pegs and string. Then, excavate to the specified foundation depth (e.g., 600mm). A concrete foundation (e.g., 200mm thick) is poured. Bricklaying then commences using a stretcher bond, ensuring vertical joints are staggered. A DPC of bitumen felt is installed 150mm above ground level. 2.2 Damp-Proof Course (DPC) and Damp-Proof Membrane (DPM)

DPC (Damp-Proof Course): As explained above, prevents rising damp in walls.

DPM (Damp-Proof Membrane): A waterproof membrane laid underneath a concrete floor slab to prevent moisture from the ground penetrating the floor. Materials used are typically thick plastic sheeting.

Importance: Rising damp causes damage to plaster, paint, and timber, creating unhealthy living conditions and weakening the structure. DPMs prevent fungal growth and keep the indoor environment dry. In South Africa, with variations in rainfall and groundwater levels, adequate damp-proofing is essential.

Installation: DPC should be laid on a level mortar bed and extend across the full width of the wall. Overlap joints by at least 150mm. DPM should be laid on a compacted layer of sand or hardcore, free from sharp objects. Overlap joints by at least 300mm and seal them with waterproof tape. The DPM should be turned up at the edges to meet the DPC in the wall. 2.3 Floor Finishes Concrete: A basic, durable finish often used in garages, workshops, or industrial buildings. Can be polished or sealed for a better appearance.

Screed: A layer of cement-sand mortar laid over a concrete slab to provide a level and smooth surface for other finishes.

The screed mix is usually 1:3 or 1:4 (cement:sand).

Tiles: Ceramic, porcelain, or natural stone tiles are widely used for their durability, water resistance, and aesthetic appeal. Suitable for bathrooms, kitchens, and living areas. Different tile sizes, colors, and textures offer various design options.

Timber: Wood flooring adds warmth and elegance to a space. Options include solid wood, engineered wood, and laminate flooring. Requires protection from moisture and scratches. Common in bedrooms, living rooms, and dining rooms.

Suitability: Bathrooms: Tiles (water-resistant and easy to clean)

Kitchens: Tiles or vinyl (durable and stain-resistant)

Living Areas: Tiles, timber, or laminate (depending on desired aesthetic and budget)

Garages: Concrete (durable and resistant to wear and tear) 2.4 Plastering Internal Walls Surface Preparation: Remove loose debris, dust, and grease from the wall surface. Dampen the surface slightly to improve adhesion. Apply a bonding agent if necessary.

Mixing Ratios: A typical plaster mix is 1:1:6 (cement:lime:sand) for the scratch coat and 1:2:9 or 1:3:12 (cement:lime:sand) for the floating coat.