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Composite decking laid on concrete

Composite decking laid on concrete

Posted by adrac on September 25, 2022

Composite decking can be laid on concrete by using the correct preparation and installation methods. We will go through the stages to set up a composite deck install on a concrete base.

Concrete is a composite of materials consisting of aggregates and cement. As the fluid bonds, the concrete hardens over time as it dries.. Concrete is the second most used material in the world, more than wood, steel and aluminium combined. Concrete remains the formidable material to use for different weather climates and structures.

Measuring and Marking for Concrete Slab Installation

To accurately position the concrete slab you will need to measure and put in place stakes to mark out the area attaching a string to join the stakes. A 100mm concrete screed in depth is recommended for a composite decking installation. For drainage and water to run a certain direction allow a 3mm fall for every 1 metre. Add or take away soil to suit the slope. Depending on the type of soil, you may need to add compacted gravel of 150-200mm if the ground is clay or soil is mostly composed of sand. This will prevent cracks and movement in the future. Place the stakes with enough height on the outer side of where the 50mm timber will go to reach above the desired concrete slab level. Once sure of the marked area check the slope of the strings and make set the string to the correct height.

Perimeter Preparation for Concrete Pouring

Place the timber around the perimeter on the prepared ground. Joining timber together on any long sides using strong bracing to ensure the concrete does not push the boards out of place when pouring. Use additional stakes to support the perimeter at approximately every 2 metres apart. Check and cover that there are no gaps underneath the timber to avoid the concrete leaking out.

In larger areas it is advisable to use reinforcement bars or rebar. This will help strengthen the concrete base and prevent cracks from appearing. Place reinforcement bars around the perimeter and then placing 1200mm apart against the direction of the slope. Use wire to connect any overlapping bars and the correct tool to cut bars to size.

Double check the weather and forecast over the next few days. If you are laying concrete in hot weather the concrete dries much faster. Create separate sections to pour in over a few days that gives you enough time to prep, mix and level the poured concrete surface. Remove the separating boards as each section dries.

Composite Deck Base Concrete Mix

Moving onto the concrete mix, a residential slab at 3500 psi (pressure expressed in pounds of force per square inch) is sufficient for a composite deck base. The mix is made up of 1 part cement, 2 1/2 parts masons sand and 3 parts stone that are about an 15-25mm in size mixed with fresh water. If required by adding more stone to weaken or less stone to strengthen the PSI. To calculate the volume of concrete required use the formula of Length x Width x Depth = Cubic Volume.

Pour the already mixed concrete into the area until you reach the desired height. Use a shovel to move across and poke in to relieve of gaps in the mix and bring water to the surface. Smooth the top surface to remove marks with a large trowel or bull float.

Allowing to set for 24 hours before walking on it and 28 days to completely cure to its maximum strength. And there we go a concrete screed to become the base for your composite decking installation.

Undertaking a project?

Deckorum Composite Decking is on hand to offer support and guidance. With domestic and commercial projects completed to the highest finish, the team is available to offer their experience.