Ask any experienced synthetic turf installer what separates a great result from a disappointing one, and the answer is almost always the same: preparation. The turf itself is only as good as what’s underneath it. Get the base right and your synthetic lawn will look fantastic and perform well for 15 years or more. Cut corners on the base and you’ll be dealing with uneven surfaces, poor drainage, and premature wear — no matter how good the turf is.
This guide walks you through every layer of a correctly prepared synthetic turf installation, from the ground up — so you know exactly what goes underneath and why each layer matters.
The Full Layer Stack — What Goes Underneath Synthetic Turf
| Layer | Material | Depth |
|---|---|---|
| 1. Native ground | Existing soil — excavated and graded | Excavate 75–100mm below finished height |
| 2. Geotextile fabric | Weed barrier (140gsm recommended) | Laid flat across entire area |
| 3. Sub-base | Road base (crushed granite or decomposed granite) | 75–100mm compacted |
| 4. Screed layer | Crusher dust or fine road base | 10–20mm — optional but recommended for a fine finish |
| 5. Synthetic turf | Your chosen Australis Grass product | Laid on top, secured at edges |
Let’s go through each layer in detail.
Layer 1: Excavation and Ground Preparation
Before anything else, you need to get the existing ground into the right condition. Start by removing all existing vegetation — grass, weeds, roots, and any organic material. Organic matter left in the ground will continue to decompose after installation, causing the surface above to settle unevenly over time.
Dig down approximately 75–100mm below your intended finished surface height. This creates room for your sub-base and screed layers while keeping the finished turf level with surrounding paths, garden edges, and structures.
Once excavated, check the area carefully for:
- Soft spots — areas that feel spongy or that hold water. These need to be dug out and filled with compactable material before you proceed. Soft spots left in place will cause visible dips in your finished lawn over time.
- Drainage issues — areas where water naturally pools after rain. If your yard has existing drainage problems, address them at the excavation stage. Adding a sub-surface drain or aggi pipe before laying your base will save significant headaches later.
- Tree roots — surface roots near trees can push up through your base layer over time. Remove as much as possible and consider a root barrier membrane in areas close to established trees.
Grade the excavated surface with a slight fall — approximately 1–2% gradient — away from your house and any structures. This ensures water drains away from buildings rather than pooling against foundations.
💡 Queensland tip: In areas with heavy clay soil (common across parts of the Sunshine Coast), clay can become very impermeable when compacted — water sits on top rather than draining through. If your site has heavy clay, consider adding a layer of coarse drainage aggregate below your road base, or installing sub-surface drainage channels before proceeding.
Layer 2: Geotextile Weed Barrier Fabric
This is the layer most DIYers skip — and the one they almost always regret leaving out.
Geotextile weed barrier fabric serves two critical functions in a synthetic turf installation:
1. Weed suppression: Without a barrier, weeds and grass will eventually push up through your sub-base and into your turf. Quality geotextile fabric physically prevents this, keeping your installation weed-free for the long term. A synthetic lawn with weeds pushing through it is both unsightly and difficult to fix without pulling everything up.
2. Layer separation: The fabric acts as a separator between your native soil and your sub-base material. Without it, fine soil particles migrate upward into your road base over time — gradually reducing drainage performance and causing the base to become unstable. The fabric maintains the integrity of each layer independently, which is what keeps your base draining and stable for the life of the installation.
We recommend a minimum of 140gsm geotextile fabric for synthetic turf installations. Our Australis Geo Fabric is 140gsm, comes in 2m x 50m rolls (100 square metres per roll), and is specifically suited to this application. It’s permeable enough to allow excellent drainage while being robust enough to last 15+ years in the ground.
Lay the fabric across the entire area, overlapping joins by at least 200mm. Use U-pins or temporary stakes to hold it in place while you add the sub-base on top.
⚠️ Don’t use light landscape fabric: The thin, cheap woven landscape fabric sold at hardware stores is not suitable for under synthetic turf. It’s too light, degrades too quickly underground, and doesn’t provide adequate layer separation. Use proper geotextile fabric at 140gsm or above.
Layer 3: The Sub-Base (Road Base)
The sub-base is the structural foundation of your synthetic turf installation. It’s what gives your lawn its firmness, stability, and long-term drainage performance. Getting this layer right is the single most important thing you can do for the longevity and appearance of your finished lawn.
What to use: Crushed granite road base (also called DGB — Decomposed Granite Base) is the most commonly used and most suitable material for synthetic turf in Queensland. It compacts firmly, drains well, and remains stable once compacted. Avoid using sand, topsoil, or organic material as a sub-base — these don’t compact properly and will shift and settle over time.
How deep: Spread road base to a depth of 75–100mm before compaction. Compaction will reduce this by approximately 20%, so you’ll need to start with more than the finished depth. For most residential installations, 100mm of loose material compacting to approximately 80mm is the target.
How to compact: Use a vibrating plate compactor — available from most hire shops for around $80–120 per day. Run it over the entire area in overlapping passes, working in different directions. Do not attempt to compact by hand or with a hand tamper over large areas — you will not achieve adequate compaction and the surface will settle unevenly after installation.
After compaction, check the surface level with a long straight edge or spirit level. The surface should be smooth and consistent, with the 1–2% drainage gradient maintained across the area. Fill and re-compact any low spots before proceeding.
Layer 4: Screed Layer (Optional but Recommended)
A thin screed layer of crusher dust or fine road base — approximately 10–20mm — applied over the compacted road base gives you a finer, smoother surface to lay the turf onto. This is particularly valuable for achieving a professional-looking finish, as it fills any minor surface irregularities in the road base that might telegraph through the turf above.
Spread the crusher dust evenly, rake it level, and lightly compact or hand-tamp it flat. This layer doesn’t need the heavy compaction of the road base — it’s a finishing layer, not a structural one.
In straightforward DIY installations on relatively flat ground, you can skip this layer and lay directly onto well-prepared road base. But for pool surrounds, visible front lawns, or any area where surface quality is particularly important, the screed layer is worth the extra effort.
What About Laying on Concrete or Pavers?
If you’re installing synthetic turf over an existing concrete slab or paved area, the excavation and sub-base layers are not required — the concrete or pavers serve as your base. However, you still need to address drainage and weed suppression:
- Ensure the concrete has adequate drainage holes or a slight fall so water doesn’t pool under the turf
- Clean the surface thoroughly to remove any moss, grease, or debris before laying
- Use adhesive or nailing to secure the turf edges rather than U-pins
- A thin foam underlay between concrete and turf can improve the underfoot feel significantly
Common Preparation Mistakes to Avoid
- Not excavating deep enough — leaving insufficient room for the sub-base means your finished lawn sits too high relative to surrounding surfaces, or the base is too thin to be stable
- Skipping the geotextile fabric — leads to weed problems and base degradation over time
- Under-compacting the sub-base — the most common DIY mistake; an under-compacted base will settle and create dips and undulations in the finished surface
- Not addressing drainage before installation — existing water problems don’t go away under synthetic turf; they get worse and are much harder to fix after installation
- Using the wrong base material — sand, topsoil, and organic material are not suitable sub-base materials for synthetic turf
What You’ll Need — Shopping List
- Crushed granite road base (calculate volume: area m² x 0.1m depth = cubic metres needed, add 20% for compaction)
- Australis Geo Fabric 140gsm (one roll covers 100m²)
- Crusher dust for screed layer (optional)
- Vibrating plate compactor (hire)
- Long straight edge or laser level
- Rake and shovel
- U-pins or temporary stakes for fabric
Everything else you need for the installation itself — turf, U-pins for securing edges, jointing tape — is available from our Baringa warehouse for same-day pickup.
Not sure about any part of the preparation process? Give Wayne a call on 0468 700 902 — we’re happy to talk through your specific site and make sure you’ve got the right materials and approach before you start digging. We stock Australis Geo Fabric, U-pins, and the full range of synthetic turf products at our Baringa warehouse on the Sunshine Coast, all available for same-day pickup.
