Why Underlay Matters. When most people think about installing synthetic grass, they focus almost entirely on the grass itself — the colour, the pile height, how it feels underfoot. And that makes sense; it’s the part you see every day. But here’s what experienced installers know: the underlay you put beneath your turf will have just as much impact on how it looks, performs, and lasts.
Get the underlay right and your lawn will drain properly, feel great to walk on, stay weed-free, and hold up for years. Get it wrong and you’ll be dealing with problems — waterlogging, weeds pushing through, or turf that shifts and looks patchy — that have nothing to do with the quality of the grass itself.
What Is Geotextile Fabric and Why Underlay Matters
Geotextile fabric — sometimes called weed mat or separation fabric — is a permeable textile laid beneath your synthetic grass before the sub-base is compacted. At Australis Grass, we supply a 140 gsm nonwoven geotextile that’s specifically suited to turf installations in Australian conditions.
It serves three important functions:
- Weed suppression: It forms a physical barrier that blocks weed seeds in the soil from germinating and pushing through your turf. Without it, even the best synthetic lawn can develop weed problems over time.
- Drainage: The nonwoven structure allows water to pass through freely while still separating layers. This is especially important in Queensland, where we can get heavy rain in a short period.
- Layer separation: It keeps your sub-base material (crushed rock, decomposed granite, or similar) from mixing into the native soil below. This maintains the integrity of your base and prevents settling and soft spots.
The Sub-Base: Your Lawn’s Foundation
Beneath the geotextile (or sometimes above it, depending on your installation method), you’ll typically have a layer of compacted crushed rock or decomposed granite. This is your sub-base, and it’s what gives your synthetic lawn its firmness, levelness, and drainage capacity.
A poorly prepared sub-base is one of the most common causes of synthetic lawn failure. If it’s not compacted properly, you’ll get soft spots, uneven surfaces, and areas where the turf sinks or ripples over time. Rushing this stage to save time or money will cost you more in the long run.
For most residential projects in South East Queensland, we recommend:
- 50–75mm of compacted crushed rock or decomposed granite
- A fall (slope) of at least 1–2% away from structures to ensure water runoff
- Geotextile fabric installed either below or above the sub-base depending on your soil type and drainage goals
What About Underlay Foam or Shock Pads?
Depending on how the space will be used, some installations also include a foam shock pad or rubber crumb layer beneath the turf. These are common for children’s play areas, sports surfaces, or any application where comfort and fall protection are a priority.
They’re not necessary for a standard residential lawn, but if you’ve got young kids playing on the surface or you’re installing turf on a hard base like concrete or pavers, a shock pad makes a meaningful difference to both safety and comfort.
Don’t Skip the Foundation
It’s tempting to cut costs on the parts you can’t see, but the underlay system is where the long-term performance of your synthetic lawn is really determined. A premium grass product laid on a poor base will never look or perform as well as a mid-range product installed correctly.
At Australis Grass, we stock 140 gsm geotextile fabric alongside our full range of synthetic turf, so you can source everything you need in one place. If you’re unsure about what your project requires, our team is happy to advise — whether you’re a DIY homeowner or a trade installer looking for a reliable local supplier.
Come and see us at Baringa, or reach out through australisgrass.com.au.
