There is a rule of thumb among landscape contractors that roughly two thirds of the cost and effort of a synthetic lawn installation happens before the turf comes off the roll. Homeowners rarely see it that way. The turf is the visible product, so it gets the attention, while the crushed rock and compaction work underneath feels like a line item to negotiate down.

That instinct is understandable and expensive. Almost every synthetic lawn failure that gets attributed to poor product quality is actually a base problem.

What the Base Actually Does

A synthetic lawn base has three jobs, and they pull against each other. It must be firm enough to stop the surface deforming under load, permeable enough to move water away quickly, and stable enough not to shift as the ground beneath it moves through wet and dry cycles.

Getting all three right requires knowing what soil you are building on. This is why a contractor who quotes a single base specification for every job regardless of site is quoting a guess.

Clay Soils

Much of Melbourne’s west, parts of Adelaide and large areas of south east Queensland sit on reactive clay. Clay swells when wet and shrinks when dry, and that movement transfers upward through anything built on top of it. Bases on reactive soils generally need to be deeper, with a well graded aggregate that locks together under compaction, and in some cases a geotextile separation layer to stop clay pumping up into the drainage layer.

Sandy Soils

Coastal Perth and parts of the New South Wales central coast present the opposite problem. Drainage is excellent, but sand offers little bearing capacity, so the challenge is achieving a firm, level platform that does not settle unevenly over time.

Existing Hard Surfaces

Laying over concrete or pavers is common on courtyards and balconies. It removes the excavation work but introduces a new requirement, which is ensuring water can still reach an outlet. A shock pad or drainage mat usually handles this, along with confirming the existing surface falls in a sensible direction.

The Layers, From the Bottom Up

A typical residential build up looks something like this, though depths vary considerably by site:

• Excavation to a depth that accommodates the full build up without raising finished levels above adjacent paths or door thresholds

• Weed barrier or geotextile, which also serves as a separation layer on clay

• Compacted aggregate, usually a road base or similar well graded crushed rock, laid and compacted in layers rather than all at once

• A finer bedding layer, often crusher dust or a fine granite screening, screeded to a smooth and accurate level

• Optional shock pad, common in play areas and anywhere impact attenuation matters

• The turf itself, joined, secured at the perimeter and infilled

The single most common shortcut is compacting in one thick lift instead of several thin ones. It looks the same on the day and settles differently within a year.

Why Falls and Levels Matter More Than People Expect

Water needs somewhere to go. On an open lawn with permeable soil beneath, the turf backing perforations and the aggregate layer handle it. In enclosed courtyards, alongside retaining walls, or where a lawn abuts a house slab, that is not enough. These situations need a designed outlet, whether that is a strip drain, an agricultural line in the base, or a considered fall toward an existing garden bed.

Choosing high quality artificial grass and then installing it over a base that traps water is the most reliable way to be disappointed by a good product.

Edges: The Detail That Gives Away Installation Quality

Look at the perimeter of any synthetic lawn that has been down a few years and you can read the quality of the workmanship. Well built edges are held by a timber, composite or aluminium restraint, with the turf secured cleanly and the pile finishing tight against the boundary. Poorly built edges lift, curl, or shed infill into adjacent garden beds.

Perimeter restraint is inexpensive relative to the total job and disproportionately important to how the lawn looks in year five.

Questions to Put to Your Installer

• What soil type is on my site, and how does that change the base specification?

• How deep is the excavation, and how many compaction passes at what layer thickness?

• Where does water exit the system, specifically?

• What perimeter restraint is included?

• Is a plate compactor or a roller being used, and why that choice?

The Bottom Line

You will never look at your sub-base again after installation day. It is nonetheless the part of the job that determines whether the surface you can see still looks right in a decade. When you are comparing quotes, the cheaper one is often cheaper because of what is happening below ground, and that is precisely the wrong place to save.