Ask any installer who’s been doing this for more than a few years and they’ll tell you the same thing the base under an artificial lawn matters more than the grass on top of it. A premium grass on a poor base will ripple and wear within a season. A budget grass on a properly built base will outlast its warranty. The choice of aggregate, the depth, the drainage gradient, and the quality of compaction all decide how the lawn behaves for the next ten to fifteen years.
This guide walks through everything you need to know to specify, choose, and build the right base whether you’re DIYing the project yourself or just want to know whether the quote you’ve been given is up to scratch.
Why the Base Matters More Than the Grass Itself
Most homeowners spend hours choosing the perfect grass and almost no time on what goes underneath. That’s backwards. The grass is the visible bit, but the base handles drainage, supports foot traffic, and keeps the surface level for the next decade. Skimp on the base and no grass will save you.
Three things go wrong when the base isn’t right: surface ripples appear within months as the ground settles unevenly, drainage fails and water pools or the lawn smells from trapped urine in pet gardens, and the edges begin to lift as the unsupported pile shifts under traffic. None of these are fixable without lifting the lawn and starting again.
What a Good Artificial Grass Base Looks Like
A properly built UK artificial grass base has three distinct layers. At the bottom, the excavated subsoil the natural ground after the old lawn and topsoil have been removed to a depth of around 75 to 100mm. On top of that sits the main load-bearing layer of compacted aggregate, typically MOT Type 1 hardcore. Above that, a smooth binding layer of sharp sand or grano dust gives the grass a flat, supportive surface to sit on.
Two further elements complete the system: a permeable weed membrane (some installers lay it under the aggregate, we always use two layers, one above and one below the hardcore), and the kiln-dried silica sand infill brushed in after the grass is laid. Together, these create a stable, draining sandwich that doesn’t shift, doesn’t waterlog, and doesn’t grow weeds from below.
Choosing the Right Aggregate for the Sub-Base
The main load-bearing layer is what people usually mean when they ask about the “base”. The standard UK choice is MOT Type 1 a graded mix of crushed limestone or granite from 40mm down to dust. It compacts to a hard, stable surface that locks together under pressure, which is exactly what you want under artificial grass.
MOT Type 3 is sometimes recommended for pet areas because it’s an open-graded aggregate without the fines, allowing urine to drain straight through rather than slowing in the dust layer. The trade-off is slightly less stability Type 3 needs careful compaction to avoid loose patches. For most domestic UK gardens, MOT Type 1 with a proper binding layer above works for both pet and non-pet use.
Alternatives include 10–14mm granite chippings or limestone chippings, sometimes used where extra drainage is essential or where access prevents the use of larger aggregates. Avoid using rubble, builders’ sand, or quarry dust as the main layer none of these compact properly or hold their shape long-term.
Sharp Sand or Grano Dust for the Binding Layer?
The 25mm layer that sits between the hardcore and the grass is called the binding or laying course. Its job is to provide a perfectly smooth, flat surface for the grass backing to rest against, eliminating any small ridges from the aggregate below. Get this wrong and you’ll see the imperfections through the pile.
Two materials dominate UK installations: sharp sand and grano dust. Sharp sand is cheaper, widely available from any builders’ merchant, and drains slightly faster. Grano dust (a fine granite quarry product) compacts to a harder, more stable finish and is what most professional installers use as standard. Either works well; grano dust is the better choice if budget allows.
The depth of this layer is fairly consistent regardless of material around 25mm, screeded flat with a straight timber edge and built with a very gentle fall away from the house at roughly 1cm per metre. That slope is what carries surface water away during heavy British rain.
How Deep Should the Sub-Base Be?
Sub-base depth depends on the use, the soil type beneath, and the climate. For most UK domestic gardens on reasonable ground, 50–75mm of compacted MOT Type 1 plus the 25mm binding layer is sufficient total dig depth around 75 to 100mm.
On heavy-use gardens (large dogs, children’s play areas, lots of foot traffic), increase the hardcore depth to 75–100mm to spread the load and prevent compression over time. For wet, clay-heavy ground that drains poorly, increase the depth further still and consider a drainage channel around the perimeter and For light use on naturally well-draining sandy ground, the minimum 50mm is usually enough.
If you’d like a measured assessment of what depth your specific garden actually needs, you can request a free installation quote and one of our team will come out and check the ground conditions before recommending a build-up.
Installing Over Concrete, Slabs, or Decking
Existing hard surfaces are some of the easiest installations to base correctly the heavy work is already done. The structure is solid, drainage is established, and excavation isn’t needed. What you do need is a foam underlay or shock pad between the hard surface and the grass.
The foam serves three purposes: it cushions the surface so it doesn’t feel like grass laid on concrete, it provides a small amount of drainage capacity, and it covers any small imperfections in the underlying surface. Cheap foam underlay starts around £6 per square metre; better-quality 10mm shock pads run £12–£18 per square metre and are worth the extra cost on patios and decks where you’ll spend time.
On decking specifically, check the boards are sound, sealed against rot, and well-supported before laying anything over them. Soft or moving boards will telegraph through the grass within months.
Drainage: Why Direction Matters Most
Most articles about drainage focus on depth and permeability. Direction matters as much as either. Surface water needs somewhere to go, and gravity is the simplest, most reliable system. Build a very gentle fall about 1cm per metre running away from the house, away from sheds and outbuildings, and toward a flowerbed, gravel border, or existing drain.
Without a deliberate fall, water finds its own path. Sometimes that’s fine. Often it’s not and waterlogged corners around fence posts, sheds, or patio joins are the usual result. Building the fall in at the binding layer stage is easy with a long spirit level and a tape measure; correcting it later means lifting the lawn. Our guide on what to put under artificial grass for drainage covers the drainage side in more detail.
Sub-Base Requirements for Pets and Play Areas
Pet gardens have one specific requirement above the standard build: drainage that handles urine reliably without holding residue. The fix is in the aggregate choice. Either use MOT Type 3 (open-graded, no fines) or an MOT Type 1 build laid slightly deeper than standard (75–100mm) so liquid drains through faster.
Children’s play areas benefit from a shock-absorbing layer between the binding course and the grass typically a 10mm or 15mm shock pad designed for play surfaces. This adds genuine fall protection without affecting the rest of the build. For mixed-use family gardens with pets and children together, the standard MOT Type 1 base with a shock pad above is the most versatile setup.
Common Sub-Base Mistakes to Avoid
A few base mistakes come up repeatedly:
- Undercompacting the hardcore. A wacker plate is essential, not optional. If your boot leaves a clear print after compaction, the surface isn’t done and will settle later.
- Wrong fall direction. Building a level base without any slope, or worse, sloping it toward the house. Surface water needs somewhere deliberate to go.
- Skipping the binding layer. Laying grass directly onto MOT Type 1 leaves the backing sitting on uneven aggregate, which shows through the pile within months.
- Using one layer of weed membrane. Bindweed, horsetail, and persistent perennials will find the gaps. Two layers crossed at right angles eliminates the problem.
- Cheap aggregate substitutions. Builders’ sand, rubble, or quarry waste don’t compact properly. Stick with proper MOT-graded aggregates.
- Skipping the wacker plate hire fee. Tamping the surface by hand never achieves the compaction you need. Hire the plate it’s £30–£50 for a day.
Where to Go From Here
The base is one of those parts of an installation that’s hard to fix once it’s wrong. Done properly, you won’t think about it again for ten or fifteen years. Done badly, it’ll annoy you within the first season.
If you’re DIYing your own install, our DIY artificial lawn guide covers the full build process step by step. If you’d like to feel different grass options before committing to a particular pile and width order a free sample pack and we’ll send a selection in the post.