Concrete slabs are popular choices for new residential and commercial builds. As opposed to building the property on stilts or stumps, a concrete base helps improve thermal efficiency, maintains the durability of the structure and allows for a larger and heavier build. The concrete slab construction process includes the preparation of formwork, compaction of a slab bed, placement of reinforcement, pouring, compacting, finishing the concrete, removing formwork and curing the concrete slab.
Following a reputable concrete floor slab construction process will ensure that the slab lasts a sustained period. Defects in construction can compromise the structure of the property and lead to expensive repairs (which may be covered by the builder’s warranty). Ensure that you engage a reputable builder who has experience.
Here is a summary of the concrete slab construction process.
The formwork is the frame for the concrete slab. For measurements, consult the approved building plans to ensure the formwork is setup correctly. Following the process of laying the formwork correctly, reduces the likelihood that the concrete slab is compromised. Preparation of formwork must also follow established building standards and guidelines.
The formwork needs to be erected correctly so that it can withstand the pressure from concrete, not leak, allow people to work and walk on it, support equipment and machines and not contain defects in construction. This means that all joints must be sealed and secured and no nails exposed. If there are any defects, costly repairs may be required. It is the responsibility of the building supervisor or site engineer to check that correct building practices have been followed.
An important tip is to ensure that the height of the formwork will be level with the top of the concrete slab so that you can screed the finished surface in line with the top of the formwork.
The site is cut to near level with excavation machinery. Once the excavation is complete, the surveyor sets pins in the ground to mark out floor area and give tradesmen points to measure from. Electricians and Plumbers trench and run access for services. Footings and piers are dug to the Engineers specifications and the site is made level using laser level. Formwork is constructed around the perimeter of the slab to be poured. This will form the shape of the slab and hold the concrete while it sets hard.
Prepare slab bedding
It is important to prepare the slab bedding correctly. This will ensure that the concrete slab rests on a firm base and that the concrete slab does not start cracking. To prepare the slab bedding, use road base or crusher dust of a reasonable thickness based on building codes. Ensure that the surface is level and flat and compacted firmly. A well-drained base and compacted bed prevents the concrete slab cracking.
Reinforcement prevents the concrete from cracking, buckling and caving in when a load is placed on it by improving the tensile strength of the concrete and making it more durable.
Ensure the reinforcement bars, spacers and ties are installed in accordance with the approved building plans.
Pour, compact and finish concrete
A professional should be engaged to pour the concrete from a reputable pre-mix company. This will ensure that the concrete is at the specified strength. Prior to pouring, soak the slab bed with water to prevent moisture loss.
Once the concrete is poured, add control joints where required. As the concrete dries, it will shrink. To avoid cracks forming randomly, control / expansion joints ensure cracks to not develop.
In addition, ensure that the concrete is compacted. This help the concrete to bind and mould into place inside the formwork and around the reinforcement bars. Vibration, either internal or external, is the most widely used method for consolidating concrete. Lastly, slabs should be finished according to applicable building standards.
Cure concrete and remove formwork
Curing a concrete slab involves the application of water over an approximate 7 day period. Applying moisture to the concrete helps it to seal. Spraying twice daily is ideal – use light mist sprays with complete coverage. After 24 hours of the concrete being poured, the formwork can be removed. Take care removing the formwork to avoid any damage to the concrete slab.
The slab can be walked on after 3 days, but avoid heavy loads for at least 7 days.
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