How do you go about ensuring that a project you’ve undertaken not only meets the quality norms, but is also finished on time and in a set budget? It can be tricky, which is why we’ve compiled the various steps in construction that will help you plan better and deliver a stellar project.
Store cement on top of wooden planks or tarpaulins spread on the floor of a weatherproof storage shed Ensure that all doors, windows and ventilators are tightly closed to prevent ingress of moisture. Ensure a gap of 30 centimetres from the wall and 60 centimetres from the ceiling to the stack Do not stack to a height more than 12 bags. Stack the cement in a length-wise and cross-wise pattern. Cover the stack with tarpaulin or polythene sheet. Use the cement bags on a first-in-first-out basis. For temporary storage at work site, stack the cement bags on raised dry platform and cover with tarpaulin or polythene sheets. Old cement (stored for more than 90 days) should be tested for its strength before use.
Start curing immediately after the concrete has slightly hardened and do it continuously. Sprinkle water on freshly laid concrete surfaces until it hardens slightly. Covered concrete surfaces like columns, sloping roofs, etc. with wet gunny bags, burlaps or straw, and ensure continuous wetness. For flat concrete surfaces like slabs and pavement, construct small bunds with lean mortar or clay. Fill it with water. Always maintain a water depth of 50 millimetres until the curing process is completed. Use water that is fit for drinking during the curing process. Cure the concrete for a minimum of 10 days in normal weather conditions,. During hot weather (greater than 40°C), cure the concrete for a minimum of 14 days.
Start the finishing operations when there is little or no water on the surface. Carry out the finishing process is the following order - screeding, floating and trowelling. Level the concrete surface by moving the straight edge back and forth across it. Keep a small quantity of concrete mix ahead of straight edge to fill the voids. While floating, use a 1.5m long, 20 centimetres wide wooden float and move it forward and backward to level ridges, fill voids and embed the coarse aggregates. Avoid excessive trowelling. Do not spread dry cement on the wet surface to absorb bleed water.
Use vibrators for effective compaction - needle vibrators for footings, beams and columns and surface vibrators for slabs and flat surfaces. Immerse the needle vertically to full depth and maintain it throughout the operation. Vibrate the concrete for about 15 seconds and withdraw the needle slowly. Ensure that the immersion points are spaced at a distance of 15 centimetres (for 20 millimetres diameter needle) Do not touch the centering plates of formwork or reinforcement with the needle of the vibrator.
Transport and place concrete within 45 minutes after the water has been added. Avoid jerks while transporting concrete to prevent separation of the materials Ensure that there is no segregation, drying-up or stiffening of the concrete while transporting. Do not disturb the alignment of the formwork and reinforcement while placing concrete. Place the concrete in horizontal layers of uniform thickness. Do not push the concrete laterally using vibrators. In case of slab-concreting, place the concrete against or towards preceding layers and not away from it. Start placing from the corner of the formwork in case of flat slabs and from the lowest level in case of sloping slabs. Do not pour concrete from a height of more than 1m; use chutes if the height exceeds 1m.
Check the inside of the mixing drum and blades for any concrete/mortar sticking to it. Introduce the ingredients in to the mixing drum without hopper in the following sequence:
In case of a mixer fitted with hopper, place the measured quantities of coarse aggregates first, then place the sand and cement into the hopper. Mix the ingredients for a minimum of 2 minutes. In case of inevitable hand-mixing, do it on an impervious platform with 10% extra cement. During hand mixing, mix the sand and cement uniformly and spread it over the coarse aggregate and thoroughly mix again until it attains uniform colour. Add water in small quantities and mix it until it becomes homogenous.
Measure the ingredients accurately to ensure correct proportions. Measuring aggregates by weight is preferable to measuring by volume. It is preferable to use Measuring Boxes of 1.25 cubic feet while measuring by volume. Fill the measuring boxes or pans up to the brim. Add sufficient quantity of extra sand (approx. 25%) if the sand is wet when being measured by volume. Measure water using calibrated cans or buckets, so that the same amount of water is used in all the batches, thus ensuring consistency.
A good brick should be hard and well burnt with uniform size, shape and colour (generally deep red or copper), homogenous in texture and free from flaws and cracks. Its edges should be square, straight and sharply defined. It should give a metallic ringing sound when stuck with another brick. It should not break when struck against another brick or dropped from a height of about 1.2 to 1.5m on the ground. No imprints should be left on the surface when scratched by the fingernail. Bricks should not absorb water more than one-sixth of its weight after being immersed in water for an hour. Good quality bricks are difficult to get and exhibit high wastage/breakage. They are not environment friendly as they consume fertile top soil. Instead, it is advisable to use concrete blocks.
Select good quality cement of a reputed brand like UltraTech Use Blended Cement such as PPC and PSC for strong, durable and environment friendly buildings. While buying the cement, please check for :
Batch Number - Week/Month/Year of Manufacturing BIS Monogram, IS Code No, MRP and Net. Weight
Ensure that the cement bags have not been tampered with.
The Right Materials for Concrete
Ensure aggregates are hard, strong and free from dust, dirt, clay, silt and vegetable matter. Remove organic matter like tree leaves, dry tobacco, grass, roots and sugar substances. Use rough/coarser aggregate for concreting. Coarse aggregate shall be roughly cubical with a combination of 10 millimetres and 20 millimetres in the ratio of 60:40 to 70:30. Do not use elongated (long) and flaky (thin) aggregates – the limit for such aggregates is 30% by mass in combination and individually 15% by mass. Select sand, which when squeezed by hand, does not leave stains and fine particles sticking to the palm. Stains indicate presence of clay and sticking fine particles indicates presence of silt. Water should be free from oil, alkalis, acids sugar and salts. Water fit for drinking is most suitable for making concrete. Seawater or brackish (salty) water should not be used for making RCC. Do not add more than 26 litres of water with each bag of cement.
Ensure that the sand is free from adherent coatings, clay, silt, dust and organic impurities. Use coarse sand for the first coat (rendering coat) and fine sand for the finishing coat. Rake the masonry joints to a minimum depth of 12 millimetres. Brush out dust and loose mortar from the raked joints as well as the masonry surfaces. Roughen the smooth surfaces that are to be plastered by wire brushing/hacking to ensure perfect bond. Clean away oily/greasy matter, plastic tapes and any other substances sticking to concrete surfaces and wash thoroughly using wire brush. Dampen the wall evenly before applying plaster. Mix small quantities of mortar such that it can be consumed within 60 minutes after the water is added. Ensure that the thickness of plaster does not exceed 15 millimetres in a single coat and 20 millimetres in two coats. Roughen the first coat (rendering coat) and keep it damp for a minimum of 2 days or until the next coat is applied. Apply the finishing coat over the rendering coat in 2 to 5 days. Cure the plastered surfaces for at least 10 days Avoid plastering in extreme temperatures (>40°C). Use well-graded sand and the most suitable proportions of cement and sand (1:3 to 1:6). Avoid excessive troweling while finishing the plaster. Avoid overworking of cement finishes to avoid shrinkage at the top layer. Lightly sprinkle water after 30 minutes of finishing the plaster surface.
Keep centering supports (ballies/props) truly vertical and brace them in both directions. Ensure that the supports have a firm base. Ensure that the spacing of supports shall does not exceed 1m centre to centre. Seal the joints of the centering plates with mastic tape. Gently coat the surface of the formwork with grease or shutter oil. Remove dust particles like sawdust, chippings and paper pieces from the formwork before placing concrete. Follow this order while removing the formwork – Remove the shuttering of vertical faces of walls, beams and column sides first followed by bottom of slabs and then bottom of beams. Keep the shuttering for a minimum of 24 hours for vertical faces of column, walls and beams. For slabs up to 4.5m span, keep the supports for 7 days; for those over 4.5m, keep them for 14 days.
Lay the blocks/bricks on a full bed of mortar and slightly press it, to ensure proper adhesion. Brick should be laid with frogs faced upwards except in top layer. Ensure that all the block/brick courses are truly horizontal and truly vertical. Stagger the vertical joints. The thickness of joints should not be more than 10 millimetres. Rake the joints to a depth of 12 millimetres, to provide key to plastering. Use cement mortar in a 1:6 proportion. The height of construction of masonry should not exceed more than 1m per day. Place rebars that are 6 millimetres in at every 4th course of masonry in half block/brick partition walls. Cure the block/brick work for a minimum of 10 days.
Use well-burnt clay bricks that are of uniform shape, size and colour. The bricks should produce a metallic ringing sound when struck together and hard enough to resist a finger nail scratch. Should not absorb more than one-sixth of their weight after one hour of immersion in the water Soak the bricks adequately in water before use, for a minimum of eight hours Should not break when dropped from a height of 3 – 4 feet.
Use concrete blocks as they are cost effectiveness, and enable faster construction, increase in floor area and eco-friendliness. They provide better insulation against sound, heat and dampness. The rough surfaces of concrete blocks provides better bond to plastering. Use of concrete blocks leads to savings in mortar due to lesser number of joints.
Treat the soil in foundations up to plinth level with approved chemicals in water emulsion. Hire a specialised agency to carry out the treatment, as it is a specialised job. Treat the soil in foundation trenches (bed and sides), plinth filling, at junction of walls and floor etc. Apply the chemical emulsion uniformly by spraying at the recommended dosages in all the stages of treatment. The treatment by the chemical emulsion varies from 5–7 litres/sq.m depending on the surfaces to be treated. Utmost care shall be taken to see that the chemical barrier is complete and continuous. Take care to ensure that the chemicals do not contaminate wells or springs and other sources of drinking water during application
A Damp Proof Course (DPC) is a horizontal barrier between the wall bottom and foundation top, designed to prevent any moisture rising from the foundation. Use 25 millimetres thick cement concrete of proportion1:1.5:3 mixed with a suitable water proofing compound in the recommended dosage. Provide DPC at a level out of the reach of any splashing water from the ground. DPC should not be less than 15 centimetres above the highest level of the ground.
Good foundations are important to ensure that no movement can take place - any movement or settlement will result in cracks in the walls. Ensure that the foundation is taken down to a firm soil. Ensure that the depth of the foundation in ordinary soils is at least of 1.2 m (4 feet). In Black Cotton (expansive) soils, the depth of foundation should be 15 centimetres below the cracks in soil. Provide an interposing layer of sand around and beneath the footing in such soils. Ensure that the width of the bottom course of the footing is not less than twice the thickness of wall. Provide a plain concrete bed (1:3:6 ratio) of at least 12 centimetres thickness below the bottom course.
Ensure correct marking of the foundations for new walls so that they are the right size and in the right position to bear the weight of the wall. Obtain the layout plan/centre-line drawing from the engineer and establish the centre-line of the longest outer wall of the building as a reference line between the pegs driven into the ground. Mark all trench excavation lines with respect to the centre lines of walls. Ensure that the excavation done is true to levels, slope, shape and pattern. Consolidate the bed of excavation by watering and ramming. Soft or defective spots should be dug out and filled with concrete. Brace the sides of excavation with tight shoring work for deep excavations to avoid collapsing of the sides of the excavation area