Estimating materials needed to build walls
This section gives step-by-step directions for calculating the materials needed to build three types of wall: poured concrete, rammed earth, and brick/block.
POURED CONCRETE AND RAMMED EARTH
To determine how much poured concrete or rammed earth he/she needs, the builder must calculate how many cubic meters of material it will take to "fill" the wall space.
Use the following equation:
Cubic meters of material needed for one wall = thickness of wall (meters) × wall area (sq. meters)
STEP 1. Decide how thick the wall will be (see page 34 for a discussion of what to consider when planning wall thickness}. Enter this figure in the correct part of the equation.
STEP 2. Calculate the wall area in square meters by multiplying the wall's length by its width.
STEP 3. Multiply the answers you found in steps 1 and 2. The result will be the cubic meters of concrete or rammed earth you will need to build that one wall.
STEP 4. Repeat steps 1 through 3 for each wall of the building.
STEP 5. Add the cubic meters of concrete or rammed earth needed for all the walls of the building. The result will be the total number of cubic meters of concrete or rammed earth you will need for the building.
Calculating Bags of Cement Needed for a Concrete Wall
Builders who plan to purchase the cement for their concrete need to know how many sacks or bags of cement to buy. Once you have determined how many cubic meters of concrete you will need, finding the number of bags of cement is easy: just look the answer up in Table 3, in Appendix 4 (page 222). To use the table, first, find the concrete mixture you plan to use. In the case of walls, the mixture would be 1:2 3/4 :4 The table will then tell you how many cubic meters of concrete you will get from one sack of cement. Divide the number of cubic meters of concrete you plan to use by the amount you would get from one sack. The answer will be the number of sacks of cement you need to purchase.
Calculating Wheelbarrowsful of Rammed Earth or Concrete Needed
Many builders want to know how many wheelbarrows full of concrete or rammed earth they must bring to the construction site for wall construction: this information gives them an idea of how much work will be involved.
The number of wheelbarrowsful needed can be estimated by following these steps:
• Build a form exactly 1 cubic meter in size and count how many wheelbarrowsful of rammed earth or concrete it takes to fill the form.
• Multiply this number by the total cubic meters of material that are needed for construction (from Step 5, page 216). Your answer will tell you how many wheelbarrowsful are needed.
BLOCK AND BRICK WALLS
To estimate the number of blocks or bricks needed to build a wall, follow these steps:
STEP 1. Calculate the wall area in square meters by multiplying the wall's length by its width.
STEP 2. Note down the nominal size of the block face. The nominal face of a block is the height and length of the block surface visible in the wall after the block is laid.
STEP 3. Use the table below to find how many blocks or bricks of the size you plan to use are needed to build 1 square meter of wall surface.
APPROXIMATE NUMBER OF BLOCKS OR BRICKS REQUIRED TO BUILLD 1 SQUARE METER WALL SURFACE
STEP 4. Multiply the number you found in the table by the number of square meters of wall surface you found in step 1, The result will be the approximative number of blocks or bricks needed to build the wall,
How many blocks would it take to build a wall with 17 square meters surface area using blocks with a nominal face 15cm x 30cm?
The table shows that 22 15cm x 30cm blocks are needed to build 1 square meter of wall area.
17 sq. meters x 22 blocks/sq. meter = 374 blocks
STEP 5. Repeat steps 1 through 4 for each wall of the building and add the results. The total will represent the number of blocks or bricks you must buy or make for the walls.
Note: Any estimate of the number of blocks/bricks needed for a building's walls arrived at through this method will include extra blocks, since the space taken by window and door openings is treated as though it were filled in with blocks. Generally it is a good idea to buy or make these extra blocks. This will give you a margin of error for wasted or broken blocks.
Calculating Mortar Quantities
The amount of mortar needed to bond the blocks/bricks for a building depends on the number of blocks/bricks and their size. To calculate the amount of mortar needed for lam thick mortar joints, follow these steps:
• Divide the number of blocks needed for the building by 100, For example, if the building requires 1,536 blocks, 1536 . 100 = 15.36.
• Use the table below to find the cubic meters of mortar needed to lay 100 blocks. For example, if the nominal size of the blocks used will be 10 cm x 20 cm x 40 cm, .073 cubic meters of mortar would be needed to lay every 100 blocks.
• Multiply the answers found in the above steps. For example, if 1,536 blocks of nominal size 10cm x 20cm x 40cm are needed for a building's walls, multiply 15.36 x .073. 15.36 x .073 = 1.12 cubic meters of mortar. Table 7 in Appendix 5 (page 224) may be used to determine how much cement, lime, and sand you will need to make the mortar required for any building.
QUANTITIES OF MORTAR REQUIRED TO LAY 100 BLOCKS/BRICKS (Mortar for Joints 1cm Thick Including 25% Allowance for Waste)
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