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There are different types of slabs used by concrete slab companies on a project site. The type used depends on the scale of the project, as well as the structural strength needed. It is best to ask your concrete slab company for information about which type of concrete slab to choose for your project.

The different types of concrete slabs include:

• One-Way Slabs on Beams: One-way slabs on beams involve assembling the formwork along with installing the reinforcements, which is then followed by the pouring of concrete. This slab type is ideal for spans of 3 to 6 metres and loads of 3 to 5 KN/square metre. Using one-way slabs for larger spans requires additional costs and higher slab deflection.
• Ribbed Slabs: Ribbed slabs are also known as one-way joist slabs. This type of slab consists of a floor slab with over 50mm to 100mm thickness. Ribbed slabs are reinforced with concrete ribs that are tapered and uniformly spaced at 750mm. Girders that rest on columns are designed to support the ribs and keep it stable. This slab type is suitable for spans of 6 to 9 metres and loads of 6 KN/square metre.
• Grid Slabs: Grid slabs, also known as waffle slabs, are reinforced with square grids containing deep sides. This type of concrete slab is appropriate for spans of 9 to 15 metres and loads of 4 to 7 KN/square metre.
• Flat Plates: Flat plates are one of the easiest concrete slabs to construct. This type can be created as one-way or two-way slabs that are supported by columns. Flat plates require simple formworks, allowing contractors to produce more on larger-scale projects. These slabs are suitable for spans of 6 to 8 metres and loads of 3 to 5 KN/square metre.
• Flat Slabs: Flat slabs are directly supported by columns without the use of beams. Similar to flat plates, this type of concrete slab requires minimal formwork. Flat slabs are ideal for spans of 6 to 9 metres and loads of 4 to 7 KN/square metre.
• Two-Way Slabs on Beams: While two-way slabs on beams are like one-way slabs on beams, this type requires more formwork to support it on all sides. Two-way slabs are appropriate for spans of 6 to 9 metres and loads of 3 to 6 KN/square metre.
• Hollow Core Slabs: Concrete slab companies offer hollow core slabs for projects where fast constructions are desired. Hollow core slabs have declined slab self-weight and enhanced structural efficiency. This can also act as service ducts. Hollow core slabs have no span restrictions with standard widths of 120mm and depths ranging from 110 to 400mm.
• Hardly Slabs: Hardly slabs are built using hardy bricks. This type of concrete slab has a thickness of around 270mm, which is thicker than a conventional slab.
• Bubble Deck Slabs: Concrete slab contractors construct bubble deck slabs by placing reinforcements between and over plastic bubbles before the concrete is poured. This type of slab reduces weight and provides additional strength.
• Composite Slabs: Composite slabs are created from reinforced concrete casts placed on top of steel decking. The span of this concrete slab can reach up to 3 metres and increase to 4.5 metres, depending on the decking’s thickness.
• Precast Slabs: Precast slabs are casted and cured in manufacturing plants. The most common precast slabs used in construction are the channel and double-T slabs. This type of concrete slab can be used for spans of 15 metres.
• Slabs on Grade: Slabs on grade are commonly cast on the surface of the earth, hence this slab type is also known as ground slabs. Slabs on grade are classified into three types: slabs on ground, stiffened raft slabs, and waffly raft slabs.

Generally, concrete slabs should be placed on an area with a depth of over 7 inches. This is to allow the placement of a gravel base with a thickness of over 3 to 4 inches for concrete.

See our blog about concrete slab thickness to find out more.

The thickness of a concrete slab depends largely on its intended use. For most residential slabs, such as those used for driveways, patios, or garages, the standard thickness is typically around 100 to 125 mm. For structures that will bear heavier loads, such as commercial floors or industrial workshops, thicknesses may increase to 150 mm or more to ensure adequate strength and durability.

Environmental conditions and the type of soil underneath the slab also influence the required thickness to prevent cracking and ensure structural integrity over time. Consulting with a professional slab concreter or engineer can provide specific guidance based on your project’s specific needs.

Estimating a concrete slab involves calculating the volume of concrete needed, which is determined by multiplying the slab's length by its width and thickness (all in metres). For instance, a slab measuring 10 metres by 5 metres with a desired thickness of 0.1 metres would require 5 cubic metres of concrete. It’s important to consider additional factors such as wastage, which is typically around 5-10% on top of your calculated volume.

Cost estimates also need to include the price per cubic metre of concrete, which can vary depending on the mix and your location. Additional costs like formwork, reinforcements, and finishing should also be factored into the overall estimate. Read our concrete slab cost guide to learn more about concrete slab estimates for your next project.

Gravel is commonly used under concrete slabs as a base layer and drainage aid. It helps to prevent soil erosion under the slab and provides a stable foundation, reducing the risk of cracking and settlement.

Gravel layers typically range from 100 to 200 mm in thickness, depending on the project requirements. This layer also facilitates water drainage away from the slab, thereby extending the life of the concrete. While not always necessary, using gravel is generally recommended for enhancing the durability and longevity of concrete installations.

Whether rebar is necessary in a concrete slab depends on the intended use of the slab and the load it will carry. Rebar, or reinforcing bar, significantly enhances the tensile strength of concrete, which is naturally strong in compression but weak in tension.

For structural slabs, driveways and areas that will support heavy loads, rebar is often essential to prevent cracks and failures. In residential settings like patios or walkways where loads are lighter, mesh reinforcement or fibre reinforcements might suffice. It's always best to consult with a structural engineer or a professional concreter to assess the specific requirements for your concrete slab.