Top Tips to Installing a Concrete Slab

Offering a workable alternative to traditional concrete foundations, concrete garden pavers, outdoor entertainment areas, seamless driveways and garage flooring, find out how to fit concrete slabs as a DIY project at home.

The beauty of concrete slabs is they can be poured and placed in just about any shape, colour or surface texture imaginable as long as the form fits the function, what’s more, placed on well prepared and compacted sub-grade, concrete slabs offer lasting durability at a fraction of the price compared to painstakingly mapping the route of intricate foundations, outdoor entertainment areas, patios and pavers.

The key to pouring a concrete slab lies in the preparation of the subgrade, where preventing cracks and fissures depends on the base the concrete settles on and how well the slab is protected from moisture absorption. Concrete slabs can be further reinforced using vapour barriers and a combination of rebar, wire-mesh or even fibre-mesh for added durability and load bearing capacity.

Placing concrete slabs at home can be a fairly simple process to follow with the devil in the detail of preparing a balanced, primed and well compacted subgrade. Together with a crushed gravel base to prevent natural sinkage from weight and added pressure and further reinforced by a level and compressed soil subgrade, concrete slab foundations and flooring will refrain from sinking or cracking even under the most extreme South African weather conditions.

Creating a concrete slab for beginners starts with the assembly of a sturdy timber frame to define the perimeter of the concrete base. Once enclosed around a well-prepared and compacted subgrade that has been finished with stone gravel, the gravel acts not only as an added layer of reinforcement on top of the subgrade but also as an effective filter preventing groundwater runoff and causing moisture to move away from the concrete slab.

Before pouring your wet concrete into place, wet subgrade slightly to avoid sucking the water out of the concrete, secure wire mesh or rebar inside your shuttered area ensure that the reinforcing is not laying on the gravel surface by lifting it to approximately centre of the slab using some bigger stones or commercially available spacers, which acts as concrete slab reinforcement, effective in increasing the load bearing capacity especially in frequent and weighty traffic zones such as driveways and garage flooring. Another detail to consider when pouring wet concrete to form a concrete slab is to do so at a very slight and gradual slope which will help water or moisture build up to run off instead of pooling in one focused depression in the slab.

Strategically beginning at the highest point of the slope, carefully pour and screed concrete into the timber frame and using a screeding tool flatten the wet concrete by sweeping the mix back and forth to create a uniform surface. Moving from the top of the slope to the bottom, create a flattened concrete surface that can then be compressed using a floating device to press aggregate gravel beneath the visible surface while offering a smoothed out and creamy finish.

Next, make use of a groover to insert measured control joints every 2 meters which will ensure the concrete slab is able to endure thermal expansion and contraction and control the position of cracks to be directed to the predetermined joints as opposed to unplanned and unsightly random cracks. (The rule of thumb is that slab sizes do not exceed the following size. Slab size must be preferably less than 32 X Thickness of slab. E.g. if you intend to cast a slab with a 100mm nominal thickness the slab / block sixe should not exceed 100 X 32 = 3.2 meters)

For outdoor concrete slab installations keep in mind that surfaces will become slippery underfoot and adding traction is considered best practice especially when surrounding wet surfaces such as pool decks, outdoor entertainment areas and garden walkways. Traction can be easily created by simply using a stiff bristle brush to sweep gentle grooves onto the smoothed surface of concrete slabs. Alternative options include incorporating decorative stamping or finishing cured concrete surfaces with a grit sealant.

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