Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Matetials and Methods used in Fixng Opening
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Matetials and Methods used in Fixng Opening
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Subject: Textile trade
Class: Senior Secondary 2
Term: 1st Term
Week: 4
Theme: Blockaying / Bricklaying
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This topic introduces teachers to the fundamental principles and practical techniques involved in fixing openings (doors and windows) within block and brick walls. Understanding these materials and methods is crucial for constructing safe, durable, and aesthetically pleasing buildings, a skill highly relevant for Nigerian learners pursuing vocational trades or simply seeking to understand the built environment around them. Proper fixing of openings ensures structural integrity, security, and adequate thermal and acoustic insulation in homes and other structures, directly impacting the quality of life and safety in Nigerian communities.
is clean and free from rust (for steel) and is square. If using pre-fabricated holdfasts, these would typically be welded onto the frame during manufacture or just before installation. Alternatively, separate holdfasts are embedded in the wall and the frame is welded to them on site. For steel frames, ensure all surfaces that will be in contact with masonry are coated with anti-corrosion paint.
3. Positioning the Frame: Place the metal frame into the opening. Use timber or metal wedges to support, plumb, and level the frame precisely.
4. Securing the Frame (Welding): If holdfasts were pre-embedded in the masonry during blocklaying, align the frame's pre-welded tabs or the frame itself with these holdfasts. Using an arc welder, securely weld the frame to the embedded holdfasts at multiple points along the jambs. This creates a very strong and permanent connection. Alternatively, using Anchor Bolts: With the frame positioned, plumb, and level, drill holes through the frame's fixing points (usually pre-drilled by the manufacturer) and into the masonry using a hammer drill. Insert appropriate anchor bolts (e.g., sleeve anchors, wedge anchors) into the drilled holes and tighten them securely with a wrench. The anchor bolts expand, gripping the masonry.
5. Infilling and Finishing: Fill any remaining gaps between the metal frame and the masonry with a strong cement-sand mortar or concrete. Ensure all welded points are protected with anti-corrosion treatment and then plastered over. Allow the infill material to cure properly. Worked
Example: Calculating Mortar Quantity for Infilling a Door Frame Scenario: A builder needs to fix a standard timber door frame (900mm wide x 2100mm high) into a 150mm block wall. The rough opening is 940mm wide x 2140mm high, leaving a 20mm gap on each side and 20mm at the top. The jambs are 50mm thick.
The infill will be 1:4 cement-sand mortar. Calculate the volume of mortar needed.
Solution:
1. Calculate the volume of the void to be filled: Side gaps (2 jambs): Width of gap on each side = (940mm - 900mm) / 2 = 20mm Height of each jamb = 2100mm Thickness of block wall = 150mm Volume for one side = 20mm (width) x 2100mm (height) x 150mm (depth) Volume for one side = 0.02m x 2.1m x 0.15m = 0.0063 m3 Total volume for two sides = 2 x 0.0063 m3 = 0.0126 m3 Top gap (lintel area): Width of top gap = 940mm Height of top gap = (2140mm - 2100mm) = 40mm (assuming 20mm at top and 20mm for head of frame itself to be filled) -> Correction: If the frame is 2100 high and opening is 2140, then there's 40mm at the top. Let's assume the gap to be filled at the top is 20mm, consistent with sides, then the head of the frame occupies the other 20mm. Depth of top gap = 150mm Volume for top = 940mm (width) x 20mm (height) x 150mm (depth) Volume for top = 0.94m x 0.02m x 0.15m = 0.00282 m3 Total Volume of Void = 0.0126 m3 + 0.00282 m3 = 0.01542 m3
2. Estimate mortar quantity: For 1:4 cement-sand mortar, 1 m3 of wet mortar generally requires about 0.28-0.3 m3 of cement and 0.9-1.0 m3 of sand, considering bulking and compaction. Let's use a simplified approach for estimation: for 1 unit of cement, 4 units of sand are mixed. Total parts = 1+4 = 5 parts. The dry volume of materials is roughly 1.3 to 1.5 times the wet volume of mortar due to voids. Let's use 1.35 as a factor. Required dry volume of mix = 0.01542 m3 1.35 = 0.0208 m3 Volume of cement = (1/5) 0.0208 m3 = 0.00416 m3 Volume of sand = (4/5) 0.0208 m3 = 0.01664 m3 A 50kg bag of cement is approximately 0.035 m
3. Number of cement bags = 0.00416 m3 / 0.035 m3/bag ≈ 0.12 bags. (This indicates a very small amount, less than half a bag). * Volume This section provides a detailed explanation of the core concepts related to materials and methods for fixing openings in blocklaying and bricklaying. 2.1 Definition of an Opening: An opening in a wall refers to a planned space created for functional purposes within a structure.
The primary types of openings include: Door Openings: Provide access and egress for people and materials.
Window Openings: Allow for natural light, ventilation, and views.
Ventilation Openings: Smaller openings often fitted with grilles, specifically for air circulation. 2.2 Essential Components of an Opening: Before frames are fixed, the rough opening must be properly prepared. Key components supporting the opening include: Lintel: A horizontal structural member placed over an opening to support the wall weight above it. Lintels are typically made of reinforced concrete (RC), pre-stressed concrete, steel, or sometimes timber. In Nigeria, RC lintels are most common due to material availability and structural strength.
Jambs: The vertical sides of an opening (door or window). The block or brickwork forming the jambs must be plumb and true to ensure proper frame installation.
Sill: The horizontal member at the bottom of a window opening. It is designed to shed water away from the wall and provides a base for the window frame. Sills are typically made of concrete, pre-cast concrete, stone, or sometimes treated timber. 2.3 Materials Used for Frames (Doors and Windows): Frames provide the structure to which doors or windows are attached, and they are critical for supporting the glazing or door leaf and securing the opening to the wall.
Timber Frames: Description: Traditionally the most common choice in Nigeria due to availability and workability. Timber frames offer a warm aesthetic and can be painted or varnished.
Types of Timber: Iroko, Mahogany, Teak, Opepe, Afara, etc. Selection depends on durability, resistance to termites/rot, cost, and appearance. Iroko is highly valued for its durability and resistance to pests.
Characteristics: Good insulation properties, relatively easy to work with, but susceptible to termite attack and rot if not properly treated and maintained.
Steel Frames: Description: Known for their strength, durability, and security. Often used for external doors, security windows, or in commercial buildings.
Characteristics: Highly resistant to fire and forced entry. Requires anti-corrosion treatment (e.g., galvanising, painting) to prevent rust, especially in Nigeria's humid climate.
Aluminium Frames: Description: Lightweight, corrosion-resistant, and aesthetically versatile. Increasingly popular for modern windows and sliding doors.
Characteristics: Low maintenance, available in various finishes (anodised, powder-coated). Offers good weather resistance but can be prone to thermal bridging if not designed with thermal breaks. uPVC (unplasticized Polyvinyl Chloride)
Frames: Description: A modern alternative gaining traction in Nigeria. Made from plastic, often reinforced internally.
Characteristics: Excellent thermal insulation, low maintenance, resistant to rot and pests, but can be more expensive upfront than traditional timber. 2.4 Materials Used for Fixing Frames: These are the hardware and bonding agents that secure the frames to the masonry.
Holdfasts (Lugs): Description: Galvanised mild steel straps, typically 25-50mm wide and 3-5mm thick, with one end shaped (cranked or splayed) to be nailed/screwed to the frame and the other end embedded into the mortar joints of the wall.
Purpose: To provide a strong mechanical anchor between the frame and the wall, resisting movement.
Placement: Usually spaced at 600-900mm vertically, with at least two per jamb side.
Anchor Bolts/Expansion Bolts: Description: Mechanical fasteners that expand within a drilled hole in the masonry to create a secure fix. Available in various lengths and diameters.
Purpose: Ideal for fixing metal frames or for situations where frames are installed into existing walls.
Mortar: Description: A mixture of cement, sand, and water, used to bed the frames, fill gaps, and embed holdfasts. A strong cement-sand ratio (e.g., 1:3 or 1:4) is recommended for fixing.
Purpose: To fill voids between the frame and the wall, providing support and a weather seal.
Concrete (Infill): Description: A stronger mixture of cement, sand, aggregates (gravel), and water.
Purpose: Used to pack larger voids between the frame and the masonry, particularly for heavy frames or for situations where frames are installed into existing walls.
Mortar: Description: A mixture of cement, sand, and water, used to bed the frames, fill gaps, and embed holdfasts. A strong cement-sand ratio (e.g., 1:3 or 1:4) is recommended for fixing.
Purpose: To fill voids between the frame and the wall, providing support and a weather seal.
Concrete (Infill): Description: A stronger mixture of cement, sand, aggregates (gravel), and water.
Purpose: Used to pack larger voids between the frame and the masonry, particularly for heavy doors or where enhanced security is required.
Wedges/Packers: Description: Small pieces of timber or plastic, typically tapered.
Purpose: Used temporarily to plumb, level, and hold the frame in its correct position during installation and until the mortar/concrete infill cures.
Nails/Screws: Used to secure holdfasts to timber frames, or to assemble frame components. 2.5 Methods Used in Fixing Frames to Block/Brick Walls: Method 1: Fixing Timber Frames using Holdfasts and Mortar/Concrete Infill This is a common and robust method for timber door and window frames.
Step-by-step Process:
1. Preparation of Opening: Ensure the rough opening in the block/brick wall is correctly sized, plumb, and level. The lintel must be properly cured. The opening should be slightly wider and taller than the frame to allow for packing and adjustment (e.g., 20-30mm extra on each side).
2. Preparation of Frame: Ensure the timber frame is square, plumb, and free from defects. Apply wood preservative (e.g., creosote, anti-termite treatment) to all surfaces, especially the parts that will be in contact with masonry, to prevent rot and termite attack. Nail or screw holdfasts (lugs) to the outer vertical members (jambs) of the frame. Typically, two to three holdfasts are fixed on each vertical side, spaced evenly (e.g., 600mm apart). The cranked end of the holdfast should point outwards, ready to be embedded into the masonry.
3. Positioning the Frame: Carefully lift and place the frame into the prepared opening. Use timber wedges (packers) at the bottom and sides to temporarily secure the frame and adjust its position.
Plumb and Leveling: Using a spirit level and plumb bob, carefully check that the frame is perfectly plumb (vertical) and level (horizontal). Adjust the wedges as necessary until the frame is accurately positioned. This step is critical for proper door/window operation. Ensure the frame is square by measuring diagonals; they should be equal.
4. Securing the Frame: Once the frame is perfectly aligned, apply a strong cement-sand mortar (e.g., 1:3 or 1:4 mix) or concrete to fill the gaps between the frame and the wall. Ensure the mortar/concrete firmly embeds the cranked ends of the holdfasts into the blockwork joints. For block walls, the mortar is often pushed into the hollow cores where the holdfasts are located. Work from the bottom upwards, filling all voids thoroughly.
5. Curing: Allow the mortar/concrete to cure for at least 24-48 hours before removing the wedges (if necessary) or applying significant stress to the frame. The frame should remain undisturbed during this period.
6. Finishing: After curing, the exposed mortar joints can be neatly finished. Any remaining wedges may be trimmed flush or removed.
Method 2: Fixing Metal Frames (Steel or Aluminium) using Welding to Holdfasts or Anchor Bolts Metal frames are often fixed differently due to their material properties. Step-by-step Process (using Welding to Holdfasts):
1. Preparation of Opening: Similar to timber frames, ensure the opening is plumb, level, and correctly sized with a cured lintel.
2. Preparation of Frame: Ensure the metal frame is clean and free from rust (for steel) and is square. If using pre-fabricated holdfasts, these would typically be welded onto the frame during manufacture or just before installation. Alternatively, separate holdfasts are embedded in the wall and the frame is welded to them on site. For steel frames, ensure all surfaces that will be in contact with masonry are coated with anti-corrosion paint.
3. Positioning the Frame: Place the metal frame into the opening. * Use timber or metal wedges to support, plumb, and level the frame precisely. to 1.5 times the wet volume of mortar due to voids. Let's use 1.35 as a factor. Required dry volume of mix = 0.01542 m3 1.35 = 0.0208 m3 Volume of cement = (1/5) 0.0208 m3 = 0.00416 m3 Volume of sand = (4/5) 0.0208 m3 = 0.01664 m3 A 50kg bag of cement is approximately 0.035 m
3. Number of cement bags = 0.00416 m3 / 0.035 m3/bag ≈ 0.12 bags. (This indicates a very small amount, less than half a bag). Volume of sand (using headpan as a common Nigerian unit): A standard headpan is approx 0.012 m
3. Number of headpans of sand = 0.01664 m3 / 0.012 m3/headpan ≈ 1.39 headpans.
Commentary: This calculation shows that only a small amount of mortar is needed for a single frame. In practice, builders would mix mortar for multiple frames or other masonry tasks concurrently. This example helps students understand the volumetric requirements and material estimation. ---
Home Construction and Renovation: Application: The knowledge of fixing openings is directly applicable to constructing new homes, renovating existing ones, or carrying out minor repairs in Nigerian communities. Understanding different frame materials helps homeowners make informed decisions based on budget, security needs, and aesthetic preferences. For example, a homeowner in a high-security risk area might opt for steel frames with specific fixing methods for enhanced protection, while a rural dweller might prioritise locally available and affordable timber with proper termite treatment.
Integration: Students can visit a local construction site or discuss with a carpenter/mason to observe actual frame installations, identifying the materials and methods learned in class. This connects theoretical knowledge to tangible, community-based projects.
Vocational Skills and Entrepreneurship: Application: Mastering the techniques of fixing door and window frames provides students with a valuable vocational skill. This can lead to direct employment opportunities as masons, carpenters, or general building technicians. Young Nigerians with these skills can start their own small businesses (e.g., "Okechukwu's Door & Window Installation Services") offering frame installation, repair, and maintenance, contributing to local economic development and reducing youth unemployment.
Integration: The teacher can invite a local artisan (carpenter or mason) to share their experiences and demonstrate fixing techniques, offering insights into the business aspect of construction. Students can role-play as a contractor and client, discussing frame choices and installation methods for a mock project.
Building Safety and Security: Application: Properly fixed doors and windows are fundamental to the safety and security of any building. In Nigeria, where security can be a concern, robust fixing methods prevent frames from being easily dislodged, enhancing protection against forced entry. Knowledge of correct fixing also contributes to the structural stability of a building, preventing issues like frames shifting or detaching from the wall, which could lead to accidents.
Integration: Students can be asked to assess the security features of doors and windows in their school or homes based on their knowledge of fixing methods. A discussion on how different fixing techniques offer varying levels of security against theft or adverse weather conditions (e.g., strong winds) would be beneficial. ---