Concrete consists of cement, aggregate (stone particles), and sharp sand. When these components are mixed with water, they form a solid, hard substance. Varying the proportions of these ingredients results in concrete of different strengths, tailored for various applications.

Achieving the correct proportions is crucial. Excessive aggregate can make it difficult to attain a smooth finish, while too much sand weakens the mix, leaving the surface vulnerable to environmental damage.

Concrete starts to harden roughly two hours after mixing, becoming unworkable shortly thereafter. However, it takes several days to achieve substantial strength and continues to harden as long as it retains some moisture.

Optimising your concrete patio involves careful consideration of these factors to ensure durability and longevity. Whether you're creating a garden patio or a stylish outdoor entertaining area, understanding the intricacies of concrete mixing can significantly impact the quality and performance of your concrete patios or driveway.

What to Expect in this guide

Designing with concrete

Estimating the amount

Designing with concrete

To ensure your concrete patios or driveways are robust, several critical factors must be considered during the design phase.

The appropriate mix type will depend on the specific use of the concrete. The concrete's thickness is dictated by the weight it needs to support. For instance, a patio for a lightweight wooden shed requires a depth of just 100mm. Conversely, for a stone, brick, or block garage, a 150mm sub-base of compacted hardcore and a 125mm concrete pad are necessary. Additionally, the pad edges must be deeper, at least 200mm, to adequately support the walls.

The concrete surface should have a slight slope to facilitate water drainage, directing water away from buildings or, in the case of a shed slab, away from the door. When laid adjacent to your house, the surface must be at least 150mm below the damp-proof course.

For areas subjected to heavy loads, such as driveways, it is advisable to reinforce the concrete with a steel grid positioned at half its depth. This reinforcement is crucial for maintaining the durability and longevity of concrete patios and other high-traffic areas.

Hand Mixing Concrete

Hand-mixing concrete is practical only for small quantities. The process is similar to mixing mortar, requiring thorough and methodical blending until achieving a uniform consistency – neither overly dry nor excessively wet. The mixture should stay on a shovel when lifted and spread slightly while maintaining its shape when dropped onto the sub-base
The appropriate mix type will depend on the specific use of the concrete. The concrete's thickness is dictated by the weight it needs to support. For instance, a patio for a lightweight wooden shed requires a depth of just 100mm. Conversely, for a stone, brick, or block garage, a 150mm sub-base of compacted hardcore and a 125mm concrete pad are necessary. Additionally, the pad edges must be deeper, at least 200mm, to adequately support the walls.

The concrete surface should have a slight slope to facilitate water drainage, directing water away from buildings or, in the case of a shed slab, away from the door. When laid adjacent to your house, the surface must be at least 150mm below the damp-proof course.

For areas subjected to heavy loads, such as driveways, it is advisable to reinforce the concrete with a steel grid positioned at half its depth. This reinforcement is crucial for maintaining the durability and longevity of concrete patios and other high-traffic areas.

Using a Concrete Mixer

Begin by pouring roughly a quarter of a bucket of water into the mixer. Add half of the aggregate and half of the sand (or half of the all-in aggregate), followed by all the cement. Check the mixture to determine if additional water is needed. Continue by adding the remaining aggregate (and sand, if applicable), and more water if necessary. For better measurement, consider using buckets instead of shovels. If the final mix is too sloppy, add more aggregate and cement in proportion. An average-sized mixer typically accommodates 12-14 shovelfuls of aggregate and 2-3 shovelfuls of cement.
The appropriate mix type will depend on the specific use of the concrete. The concrete's thickness is dictated by the weight it needs to support. For instance, a patio for a lightweight wooden shed requires a depth of just 100mm. Conversely, for a stone, brick, or block garage, a 150mm sub-base of compacted hardcore and a 125mm concrete pad are necessary. Additionally, the pad edges must be deeper, at least 200mm, to adequately support the walls.

The concrete surface should have a slight slope to facilitate water drainage, directing water away from buildings or, in the case of a shed slab, away from the door. When laid adjacent to your house, the surface must be at least 150mm below the damp-proof course.

For areas subjected to heavy loads, such as driveways, it is advisable to reinforce the concrete with a steel grid positioned at half its depth. This reinforcement is crucial for maintaining the durability and longevity of concrete patios and other high-traffic areas.

Ready-Mixed Concrete

For large concrete patio projects or when time is limited, ready-mixed concrete is a highly convenient option. Delivered by lorries, the concrete can be poured directly onto the area or transported via wheelbarrow from the lorry. While this method is more costly, it significantly reduces labour and allows for precise quantity delivery. Ensure everything is prepared before the lorry's arrival and have adequate assistance ready. Ready-mixed concrete is ordered by the cubic metre; it is wise to add 10% for wastage and specify the intended use to ensure the correct mix is provided.

Incorporating these methods, whether hand mixing for small jobs or opting for ready-mixed concrete for larger concrete patio projects, ensures efficient and effective results.
The appropriate mix type will depend on the specific use of the concrete. The concrete's thickness is dictated by the weight it needs to support. For instance, a patio for a lightweight wooden shed requires a depth of just 100mm. Conversely, for a stone, brick, or block garage, a 150mm sub-base of compacted hardcore and a 125mm concrete pad are necessary. Additionally, the pad edges must be deeper, at least 200mm, to adequately support the walls.

The concrete surface should have a slight slope to facilitate water drainage, directing water away from buildings or, in the case of a shed slab, away from the door. When laid adjacent to your house, the surface must be at least 150mm below the damp-proof course.

For areas subjected to heavy loads, such as driveways, it is advisable to reinforce the concrete with a steel grid positioned at half its depth. This reinforcement is crucial for maintaining the durability and longevity of concrete patios and other high-traffic areas.

Estimating the amount

Determining the amount of concrete required for concrete patios involves some basic geometry. Start by measuring the surface area of your site: multiply the length by the width (in metres). Then, multiply this figure by the desired depth or thickness (in metres) to obtain the volume in cubic metres.

In practice, it's advisable to round up your figures and add approximately 10% to account for wastage. For instance, for a site with a width of 2 metres, length of 6 metres, and a depth of 0.15 metres, the calculation would be: 2m x 6m x 0.15m = 1.8 cubic metres. This should be rounded up to 2 cubic metres of concrete.

For circular sites, use the formula πr² (where π = 3.14 and r² is the radius squared). Multiply these values to get the surface area, then multiply by the depth of the concrete to find the volume. For example, with a radius of 2 metres and a depth of 0.15 metres, the calculation is: 3.14 x 2m x 2m x 0.15m = 1.884 cubic metres. This rounds up to 2 cubic metres of concrete.

For irregularly shaped sites, accurately draw the shape to scale on graph paper, with each square representing one square metre of the site. Count all the full squares and estimate the total of the partial squares. Multiply this total by the depth of the concrete and add 10% for wastage.
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