Can You Lay Composite Straight on Concrete?

Henry A
install composite decking on concrete

Composite decking boards are beautiful, durable, and low-maintenance. It’s one of the best flooring options for outdoor garden spaces. Because of this, you may have thought of installing one on top of your old concrete slabs. The question is, can you lay composite decking straight on concrete? Yes, you can lay or install composite decking on concrete if you want to.

Concrete is an excellent foundation for other floorings. If you are tired of how your garden looks with concrete slabs, you can up its appeal by building a decking area. However, you cannot install Ultra Decking composite boards directly on top of the concrete. You will need to create a frame first. The question is, how do you build a decking frame on concrete?

Can You Install Composites Directly on Concrete?

Despite many of its advantages, concrete paving is not the best choice for outdoor living spaces, especially if you aim for a beautiful and luxurious garden. So you may have thought of installing composite decking on top of it. The concern of many is, can you do that without any consequences?

The answer depends on various factors. Straight and level ground is one of the perfect places to install composite decking. However, there are things that you should consider. If the place is not levelled, you may need to use adjustable pedestals to level the installation area. You will also need to solve the potential problem of water pooling by making a drainage system.

Of course, sometimes, installing decking on concrete isn’t a good idea. For instance, if the concrete slab has cracks, it risks sinking, along with the composite decking that you’ll be installing on top of it. Also, many experts don’t recommend laying composite decking on low concrete slabs, as water pooling can be a potential issue.

How to Install Composite Decking on Concrete

Can You Lay Composite Straight on Concrete

If you decide to install composite decking on concrete slabs, here are several ways you can lay decking over concrete. However, keep in mind any instructions supplied to you by your board’s manufacturers.

Before anything else, you will want to check the concrete slab for any potential water pooling issues. You may need to put a slight slope on the concrete slab, away from the house. One way to achieve this is by using a self-levelling compound or a concrete topping mix. You can also caulk the concrete slab, which will prevent it from absorbing water. You will also need to level it first if you have uneven ground.

Using a Sleeper System

The next thing you’ll need to do is to create the layout for your decking. For composite decking over concrete, you can use a sleeper system. Mark the concrete slab and the corresponding sleepers according to the design and layout of the decking that you want. A more complicated decking will require more, especially if you plan to add stairs and railings.

After setting up the layout, you’ll want to pre-drill concrete screws for the sleeper system. Drill the screws at least 1 inch in depth. Many also advise pre-drilling at least 1/4 inches deeper than the screw can reach, making it easier to drive them into place.

Next, start installing the sleeper system. If you are using this method, you will want to use water-resistant materials and make sure that the concrete slab is free from issues. For composite decking, many recommend using at least pressure-treated wood. The sleepers should at least be 1 1/2 inches in height and width. While you can follow the concrete slab’s slight slope, you can also use spacers to level it. Secure the sleepers in place by drilling them into the slab carefully.

Fix any Drainage or Water Pooling Issues

You will need to fix any drainage problems, such as pooling and water run-off. If your concrete slab is not flat, you may need to resurface and level it.

After checking and fixing issues with the concrete, it is now time to mark the layout of the sleeper. Pre-drill holes on the surface carefully. You do not want to crack the concrete.
Next, install the sleepers on the concrete, ensuring that the screws penetrate the concrete at least a 1/2 inch deep. For best results, make sure to get rot and moisture-resistant sleepers, especially if you live in a rainy or snowy area.

After installing the sleepers, drill the sleeper joists according to the instructions. In most cases, you will need to space the joists by no greater than 300mm in the centre. After installing the sleeper system, it is best to add protection by covering it with damp proof course (DPC) tape. It prevents the material from absorbing too much moisture, which is quite helpful if you are using wood rather than composites.

Lastly, install the joists of the sleeper system. The joists should be parallel to the slope of the concrete slab. You can finally install the composite decking boards. Follow the directions supplied to you on how to do it.

Use Composite Decking Tiles

Another way of installing composite decking on concrete is by using composite decking tiles. For this, you will still need to level and waterproof your slab. However, installing it is easier, as you can lay them on the surface straight away. You may need a saw to cut the tiles according to the shape of the layout of your planned decking.


Can you lay composite decking straight on concrete? Yes, you can lay or install composite decking on concrete if you want to. Composite decking is beautiful, durable, and low-maintenance. It’s one of the best flooring options for garden living spaces.


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