Tips on Good construction practices

Remember, there is only one way to build a quality home - and that's d oing it the right way at every stage.

Layout excavation and soil filling

Mark the boundaries prior to excavation. Use a right angle and line-string to mark perpendicular lines at various distances for foundations and columns. Always maintain the depth and level of the excavation with water and plinth level.

Sometimes, the underground water seeps into the foundation pits. Drain out the water before the foundation concrete is cast. Creating drains beside trenches or shallow sumps at the corners is recommended. The water collected in the trenches/sumps can then be drained using a dewatering pump or bucket.

You will have to excavate until you reach the hard strata, as indicated in the design drawings. Clean and water the bottom surface, before it is rammed. It is advisable to lay 2-3 inch thick plain cement concrete below the RCC foundation.

In case of black cotton soil or soil types with low load bearing capacity, use pile foundations or continuous foundations. Fill in the trench up to the floor level when the foundation is cast or plinth is constructed, by soil filling. Murram filling is a good choice. Filling should be done in layers of maximum 6" thickness, sprinkling each soil layer with water before compaction, using a ram or plate compactor. If murram or good quality clay is not available, use sand for filling with adequate watering.

Steel rods, cover blocks and shuttering

Plain concrete without steel or other reinforcements is strong in compression, but weak in tension. Steel is one of the best forms of reinforcement to take care of stress and to strengthen concrete to bear loads. It forms the basis of the concrete structure and is generally laid out in a circular cross section.

Steel rods should be free from loose rust, oil paints, and mud and cut, bent and fixed properly. The bars should be placed and maintained in position by using proper cover blocks, spacers, supporting bars and laps.

For general house construction, 6 to 20 mm diameter bars are used. Mild steel bars and deformed bars are used, with the latter used most commonly nowadays, because of higher strength and the reduced requirement of steel.

Thermo-mechanically treated (TMT) and corrosion-resistant steel (CRS) bars with added features have been introduced recently. Remember to purchase ISI certified steel bars from reputed manufacturers, regardless of the size you choose.

Lap length

Lap length is provided at the junction where an old bar that terminates and joins the new extension bar. Lap length of about 50 times the diameter of the bar is considered safe. All laps should be staggered and not provided at one place. A maximum of 50 per cent bars should be lapped per section.

If the required lap length is not available at the junction owing to space and other constraints, couplers or the correct method of welding should be used to join the bars.

Anchorage length

This is the additional length of steel of one structural member necessary for insertion with another member at the junction. For example, the beam with the pillar, or the pillar with the foundation. The required length is similar to the lap length mentioned above or as per design instructions.

Cover blocks

Cover blocks are placed to prevent the steel rods from rusting due to exposure to air, and to fix the bars in place. Sometimes during the concreting activity, the covers tend to get displaced. To prevent this, tie the cover block using thin steel wires called binding wires to the steel bars. Covers should be made of cement and sand mortar (1:3, 1 part cement and 3 parts sand by volume). The blocks could be cubical or cylindrical in shape. Normally, cubical cover blocks are used. As a thumb rule, a minimum cover of 2" in footings, 1.5" in columns and 1/2" to 3/4" for slabs and beams is recommended.

Shuttering

The formwork or shuttering should be rigid and closely fitted with sufficient strength to support wet concrete. It should be leak proof to prevent the cement-sand-water mix from leaking. The face of the formwork should be treated with form release agents available in the market or a mixture of diesel and grease.

Deshuttering

Removal of shutters (deshuttering) results in concrete being subjected to loads and exposure to the atmosphere. If the ambient temperature is above 15 centigrade and the workmanship is good, the following striking / deshuttering period is considered safe.