Can you lay composite decking on concrete? | Installing WPC without demolition.

Is a concrete base suitable for a WPC patio?

Yes – provided it meets a few key requirements. Composite decking boards can be installed on an old concrete slab without any problems if:

• the base is stable and not cracked,
• the surface is level or can be levelled,
• the slab allows water to drain away (a slight slope of at least 1–2%),
• there are no damp problems (e.g. no damp-proofing).

If everything checks out – you’re ready to go! 

Benefits of installation without removal. 

Why install a WPC patio on concrete, without breaking up the old surface?

• Save time and money – no demolition work or rubble removal.
• Quick installation – there’s no need to wait for a new concrete slab; you can get started straight away.
• Appearance – WPC decking boards look like wood but do not need painting.
• Durability – resistance to moisture, frost, UV radiation and mould.
• Eco-friendly – many WPC decking boards are made from recycled materials.

Common mistakes – and how to avoid them. 

• Lack of insulation – if the concrete draws in moisture, it is worth using a sheet or membrane beneath the joists.
• Insufficient slope – this can lead to water pooling and algae growth.
• Rigidly fixing the joists – this can cause cracking when temperatures change.
• Lack of expansion gaps – composite decking expands in the sun, so it needs room to expand.

Step by step: installing a WPC patio on concrete.

1. Assessing and preparing the base. 

• Clean the concrete of dust, moss, old adhesive and loose fragments.
• Check the level – use a spirit level or a long straightedge.
• If the slab has minor unevenness, use rubber pads beneath the joists.

2. Laying the joists. 

• We do not install decking boards directly on concrete – composite or aluminium joists are needed.
• Lay the joists 30–40 cm apart, perpendicular to the direction of the decking boards.
• Do not rigidly fix them to the concrete – it is best to use rubber pads or special supports, which: 
  • • • • • •  improve water drainage,
            • minimise noise and vibration,
            • prevent the decking board from coming into contact with moisture.

3. Installing composite decking boards. 

• Fix the decking boards to the joists using fixing clips – this creates a neat, even finish. 
• Remember to allow for expansion gaps – leave at least 5 mm between the decking boards and around 10 mm from the walls.
• Check every few decking boards with a spirit level to make sure the whole surface is even.

4. Finishing touches. 

• To finish, you can install end trims, end caps or side cover trims.
• All this helps the patio look modern and be 100% protected. 

In summary – WPC decking on concrete? It works!

Wondering whether it’s worth investing in composite decking without removing the old concrete? Definitely. It’s a proven way to achieve a quick, durable and modern renovation without complex building work. With joists, fixing clip systems and a well-prepared sub-base, your terrace will gain a fresh look and new functionality – without mess, stress or demolition.

FAQ – frequently asked questions. 

Do I need to fix the joists to the concrete?
No. They simply need to rest securely on rubber pads or supports.

Can ordinary wooden boards be used instead of WPC?
Yes, but they will need regular treatment and are less resistant to moisture than composite.

How long does it take to install this type of terrace?
On average, 1–2 days, depending on the size of the area and the installer’s experience.

Does WPC heat up?
Yes, like any synthetic material – but less than dark tiles. You can walk on it barefoot.