It is tempting to think the grass is what matters most when you are choosing an artificial lawn. It is not. The single biggest thing that decides whether your lawn stays flat, firm and well-drained for years is what goes underneath it. A good base can make a mid-range grass look and last brilliantly; a poor base will ruin even the most expensive turf. This guide walks through what a proper base is made of, how deep it should be, and the mistakes that catch people out.
Why the base matters more than the grass
Think of the base as the foundations of a house. You can pick a lovely grass with a soft, natural pile, but if it is laid on soil, a thin scatter of sand or an uneven surface, it will dip, ripple and hold water within a season. The grass is the part you see, yet it is the part doing the least work.
The base is what carries the weight, keeps the surface level and lets rain drain away. Almost every lawn that fails early fails because of the ground beneath it, not the grass on top. Spend your attention here and the rest follows.
What goes into a good base, layer by layer
A proper base is built up in stages, each with a job to do. Here is what a sound installation looks like from the bottom up.
Excavation
First the old lawn or surface is dug out, usually to a depth of around 75 to 100mm for a domestic garden. This clears the turf, roots and soft topsoil, and makes room for the stone that follows. Skip this step, or dig too shallow, and there is simply nowhere for a stable base to sit.
The MOT Type 1 sub-base
Next comes the heart of the base: a layer of MOT Type 1, a crushed stone that compacts into a firm, free-draining bed. It is laid and compacted in layers rather than all at once, because a single thick dump of stone never compacts properly through the middle. This is the layer that gives the lawn its strength and its shape.
The levelling layer
On top of the stone goes a thinner layer of sharp sand or granite dust, screeded smooth and compacted. This is what gives the grass its final, even surface, because the stone sub-base is too coarse to lay grass straight onto. Granite dust is a popular choice as it binds tightly and drains well.
The weed membrane
A weed-control membrane is laid to stop anything growing up through the lawn. The sheets are overlapped by around 100mm so nothing finds a gap between them. Depending on the installer’s method it may sit on the sub-base, under the grass, or both. Done properly, it keeps the lawn clean from below for its whole life. You can see how these layers come together on our ground preparation page.
How deep should the base be?
For a normal garden walked on by people, a compacted MOT Type 1 sub-base of around 75mm, plus the levelling layer on top, is the usual standard. That gives a firm, stable surface that will not shift underfoot.
Where the lawn will carry more, such as a driveway edge, a spot where heavy pots or equipment sit, or ground that was very soft to start with, the base is built deeper and compacted in more layers. The softer or wetter your ground, the more base it needs to stay put. A good installer judges the depth from what they find when they dig, not from a one-size figure.
Why falls and drainage are built into the base
A proper base is never dead flat. It is laid with a slight slope, or fall, so that water drawn down through the grass is guided gently away rather than left to pool. This camber is set during the levelling stage and is almost invisible once the grass is down, but it is doing quiet, important work every time it rains.
Because the stone and sand are free-draining, water passes straight through the base and soaks into the ground below. On heavy clay or waterlogged plots, extra drainage such as a soakaway or French drain may be added at this stage too. Building drainage into the base from the start is far easier than trying to add it later, and our drainage guide explains why.
Common base mistakes
Most base failures come down to the same handful of shortcuts. The ones we see most often are:
- Digging too shallow, which leaves no room for a stone base that can do its job.
- Laying stone in one thick layer instead of compacting it in stages, so the middle never firms up.
- Skipping the compaction, which means the base settles unevenly once people start walking on it.
- No falls for drainage, leaving water to sit and the lawn to feel spongy.
- Laying grass straight onto soil or old slabs with no real base at all.
Each one is invisible on the day the lawn is finished. They only show themselves weeks or months later, as dips, ripples and puddles, by which point the fix means lifting the lawn and starting again.
Can you lay artificial grass without a proper base?
You can lay it, but it will not last. Grass dropped straight onto soil will sink and ripple as the ground moves and the soil softens with rain. Grass laid on a thin layer of sand with no stone beneath it has nothing to hold its shape. It might look fine for a few weeks, and that is exactly what makes the shortcut tempting.
The one honest exception is a sound, well-draining hard surface such as a patio or concrete slab, where the grass can be bonded down instead of built on stone. That is a different method with its own rules. For everything else, the base is not the part to save money on. It is the part that makes the whole lawn work. If you want to see how the full job comes together, our installation process page walks through it step by step.
Frequently asked questions
How long does it take to build a proper base?
On a typical domestic garden, the groundwork takes up most of the job, often a day or two before the grass even goes down. Digging out, carting away the spoil, laying and compacting the stone, then screeding the levelling layer all take time. If someone promises a full lawn in a few hours, the base is usually where the corners are being cut.
What is MOT Type 1 and why is it used?
MOT Type 1 is a crushed stone with a mix of sizes, from larger pieces down to fine dust. When compacted, the dust fills the gaps and locks the stone together into a firm, stable layer that still lets water through. That blend of strength and drainage is exactly what an artificial lawn needs, which is why it is the standard choice for the sub-base.
Do I need a different base for a lawn the dog will use?
The structure is the same, but drainage matters even more. A free-draining base lets water (and the rinse-down you give it) pass straight through, which keeps odours from building up. Some installers add a slightly deeper or more open base layer for dogs. Our page on grass for dogs covers the detail.