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Install Composite Decking on Grass

Install Composite Decking on Grass

Posted by Deckorum Admin on March 4, 2023

Install Composite Decking on Grass


Installing a deck on your property is a great way to perfect an outdoor space at your home. To ensure your deck is built strong and structurally safe on grass, it is important to properly prepare the ground before install composite decking. We have put together some tips on how to prepare the ground for installing your new deck on soft ground such as grass.


Remove the Grass

We start by removing any existing plants and debris from the area of installation. If there is any existing shrubbery, such as grass or weeds, you will need to remove these so they do not grow out from the under deck. If you are covering a large area you can hire a sod cutter to remove the grass and alternatively a fork/shovel to remove any weeds and smaller area. Once the plant life has been removed, you will need to rake the area to clear any undergrowth such as roots and level to a suitable condition that will allow the commencement of placing the joists together.


Level the Ground

To level the ground especially if the ground is uneven, you will need to use a shovel to level it out and rake the top layer to move ground into specific areas. The tool you can use are a carpenter’s level to check that the ground is even as you progress. This step is important to confirm that the ground is as level as possible to future proof your deck and so it does not become uneven over time. At this stage prepare by digging where the posts will be placed if a raised deck or mark out where the supports will be positioned as this will help avoid covering the marked positions.


Weed Membrane

Once level it is recommended to install a weed barrier. This is to prevent weeds or grass from regrowing in the area. The best option to use is a weed membrane that will act as a weed barrier yet allowing water to flow through into the ground and reduce water to sit on the surface. This will also help to keep the area looking neat and tidy. Weed membrane is available in different widths and lengths so it best to get enough weed membrane fabric to cover the edges and overlap comfortably without any gaps.


Moisture Levels

As a precautionary measure check for surface water and moisture in what used to be the grass area. It’s essential to ensure that the ground is not excessively wet or damp before placing joists in a structure. A check can be made by observing and walking over the ground to determine if the soil is sufficiently dry. If the ground has water sitting or damp to cause mud, If using timber this can cause the wood to rot prematurely and cause the substructure to become unstable. Soil moisture levels can be checked by observing and walking over the ground. A dry soil also means that it’s an appropriate time for laying the joists of the deck. However, if the soil is damp, it may require additional time to dry out before starting the construction.


Compact the Ground

Now the area is ready to compact the ground. Laying joists directly on soft ground is not advisable. The ground needs to be compacted first to provide a stable base for laying the joists. For larger areas, a whacker plate can be used to compact the ground effectively. A hand tamper can be used to compact smaller areas of the ground effectively. Alternatively, the ground can be compacted by walking over it on the heels of the feet to achieve a firm and stable base. The transformation of soft ground into hard ground creates a stable foundation. This foundation can then be used as a base for laying the joists of the deck.


Mulch or Gravel Layer

Making sure the ground remains firm and can disperse of water more easily it is recommended to add a mulch or gravel layer above the weed membrane fabric. This will help with drainage and provide a settled base for longer. Water passing through the layer of mulch or gravel gets partially absorbed. This absorption allows for a more controlled and steady seepage of water into the soil.

The recommended depth for the layer of mulch or gravel is about two to three inches (5 – 7.5cm). This depth should be applied uniformly across the entire area. For every 10 square metres you would require approx. 500 – 800 litres of mulch or 850kg – 1250kg of gravel. To even out the material use a rake to distribute the gravel evenly across and making sure it is levelled although not overly important to be perfect as the supports or posts will need to be on or in the harder ground which is level.

Now that the ground is prepared you can initiate a plan and lay the decking substructure. See our blog on substructure materials available that are best suited to grass. Also view our installation guide on how to lay the substructure at various heights. Once the substructure is complete, the composite decking can be laid down. It should be fixed with appropriate fasteners to ensure a stable and secure substructure. The decking must be laid on a properly constructed substructure to ensure durability and longevity. The foundation must remain strong to resist weather and time effects on the substructure.

By using these steps, it can safeguard that the ground is correctly arranged for a composite decking install. Following the setup will improve the deck life and that it is built to last and looks great.