Yes – you can install your deck over the concrete, but it must be installed on a subframe.
Laying composite decking over a concrete slab is a practical way to transform an existing surface into a stylish, low-maintenance outdoor space. With the right preparation, materials and method, you can create a deck that looks great, drains properly and lasts for years. We’ll walk you through the best options to attach your decking and the alternatives available.
Why Homeowners Choose to Deck Over Concrete
Concrete slabs are common in Australian backyards, patios and balconies. Like many things, they require ongoing maintenance to keep them looking presentable, but sometimes, they are just too old, cracked and worn to salvage. Rather than removing or replacing the slab, decking over it provides a quick and cost-effective way to refresh outdoor areas. Composite decking is particularly popular because it’s low-maintenance, durable and resists warping, fading and wear.
A deck adds style and character and turns an average outdoor space into something special. It also adds value to your home when you go to sell.
Decking over concrete also allows homeowners to upgrade the comfort and aesthetics of their outdoor areas without major construction works. Whether you want a seamless extension of your home or a complete backyard makeover, composite decking delivers a beautiful finish while staying resistant to whatever the outdoors can throw at it.
Assess Your Concrete Slab
Before installing any decking, check the condition of your concrete slab. Ensure the surface is level, structurally sound and free of cracks or spalling that could compromise the subframe. Poorly prepared concrete can lead to uneven decking, squeaking boards or accelerated wear.
Drainage is crucial. Water should not pool on the concrete, as trapped moisture can affect the decking and subframe over time. If necessary, slope the slab slightly or install a drainage layer beneath the subframe to prevent water accumulation.
Concrete slabs that are too low or too uneven may require adjustment of the subframe height or the use of pedestals to achieve a level, stable deck surface. NewTechWood’s NIVO Decking Pedestals are designed specifically for this purpose, providing a simple, convenient and adjustable way to level your deck over when slabs are sloped or uneven.
Can You Glue Composite Decking Directly to Concrete?
No; composite decking must never be glued directly to concrete. Gluing boards eliminates the expansion gaps and underboard airflow that are essential to the decking’s structural performance. This risks warping, moisture damage and premature failure. Importantly, it also voids your manufacturer warranty.
The only safe, correct installation method is to follow NewTechWood’s official installation guide, which details the proper subframe setup, fastening system and spacing requirements that ensure your deck performs as intended for years to come. Read the full NewTechWood Decking Installation Guide here.
How to Install Composite Decking Over Concrete, Step-By-Step
Measure ground clearance above concrete
Determine the total height that your deck needs to sit above concrete. Include any allowances for drainage, ventilation and board thickness. This lets the deck sit level, clears obstacles like door thresholds and allows water to flow freely beneath.
The minimum ground clearance over concrete for NewTechWood composite decking is 40mm.
Is your proposed deck going to be an acceptable height for your existing door threshold, given the height of your existing concrete patio? Ideally, when you walk off your doorstep, you want to either step down to your deck or at least be level with it – you do not want to be stepping up to it.
Levelling the surface
Use a spirit or laser level to check for dips or high points in the slab. Consider smoothing out any uneven areas in the concrete using a fast-drying levelling compound or ready-mixed concrete. Don’t worry about how “pretty” your handiwork is because the deck will cover it.
Any minor unevenness can be corrected with adjustable decking pedestals or shims placed beneath the subframe. These are a quicker option, accurate and much less messy than cement levelling compounds.
Achieving a properly level surface ensures the decking boards sit evenly, prevents squeaks and minimises the need for future maintenance.
Attach your metal or timber subframe
Install a corrosion-resistant metal or treated timber subframe over the concrete, following manufacturer spacing and anchoring guidelines.
For our purposes, we will just talk about NewTechWood’s composite deck construction requirements.
Depending on the decking profile board you have chosen, the decking span required for residential projects will range from 350mm for UH02, 450mm for US49, and 400mm for US54. Deduct 100mm from these measurements for commercial projects. Note: The span for NewTechWood’s specific commercial decking board, the US71, is 600mm.
Once you’ve taken the appropriate measurements and marked out where your sleepers will be placed on the concrete, you will attach the sleepers to the concrete using dynabolts and strong steel brackets. Check the level as you go, and if you discover any low areas you missed previously, you can use plastic shims to fill the gap and even it out.
Make sure the subframe is level and has been securely fastened. Air circulation beneath the subframe is essential to prevent moisture buildup and maintain the decking’s longevity.
Lay the composite decking boards
Position the boards according to the manufacturer’s recommendations, maintaining the required expansion gaps between each board and at the perimeter. Secure boards with hidden fasteners or screws specifically engineered for composite decking. Consistency in the spacing and alignment leaves a clean, professional finish.
Finishing touches
Add trim boards, fascia panels and end caps where needed. Check for loose screws, alignment issues and proper spacing. Inspect the deck surface and subframe for stability before use. Once complete, your deck will have a professional finish and be fully ready for outdoor use.
Consider Using Composite Deck Tiles Over Concrete
Composite deck tiles offer a practical alternative for concrete surfaces, especially where a temporary or easily removable solution is needed. Unlike full decking boards, tiles require no subframe, so they can be installed directly on the slab. This makes them ideal for rentals, patios or spaces where you want a quick upgrade without permanent alterations.
Each tile locks into place, allowing for modular layouts that can be adjusted or removed as needed. They provide a consistent, level surface, improving safety and usability on otherwise plain concrete. Tiles are also fully compatible with any drainage needs, as water can flow beneath without causing damage.
NewTechWood Products Suited for Concrete Installations
When installing over concrete, the right product ensures performance and longevity. Choosing the right product means that your deck will remain durable, visually uniform and low-maintenance even under heavy use or in Australian weather conditions.
NewTechWood’s Avenue, Coastal and Terrace ranges are engineered for direct concrete installations, offering composite boards that resist warping, fading and everyday wear.
These boards provide a stable, level surface and maintain consistent expansion gaps, which is critical on a non-porous slab. Each range offers different textures, profiles and colours, letting you match the deck to your outdoor space without sacrificing structural integrity.