The best sub-base for artificial grass is a subject for debate among artificial grass installers. Whilst it is possible to use granite or sand, environmental conditions have to be accounted for.
Sometimes, granite will be the best option, other times it will be better to use sand. For residents in the UK, granite is generally preferred because it doesn’t retain as much moisture as sand.
The importance of a strong sub-base cannot be overstated. It is not a step you want to get wrong. If the foundations are not laid correctly, your artificial lawn will generate lumps and create puddles of water.
A sub-base must be laid with irrigation in mind. It must allow water to drain away efficiently and prevent seeds from sprouting beneath the fake grass installation. Weeds and plant bulbs create lumps on your lawn.
Getting the right aggregate makes all the difference. In this article, we look at the pros and cons of using granite dust and sharp sand.
Is granite dust a good sub-base?
The purpose of a sub-base is to retain density, allow permeability and allow excessive amounts of water to drain through without compromising the foundational structure.
In most cases, a combination of MOT Type 1 granite and granite or limestone dust ticks all the boxes. Stone dust compacts better which avoids your artificial lawn from acquiring ridges and lumps, and also allows water to drain through.
MOT Type 1 is the best sub-base material for strength and compaction. Although it helps with drainage, MOT Type 1 is not a permeable material. This means that water drains at a very slow rate. Rainy days can cause your fake grass to collect water.
The solution to avoid water pools is to combine MOT Type 1 granite with granite chippings. 2mm stones work well. The level of compaction of using granite chippings alone will not offer substantial support for artificial lawns that receive heavy or frequent traffic, but it does enhance drainage.
For commercial properties and home installations used for playing football, we recommend using 75mm of MOT Type 1 and 25mm of Granite dust. Increase the overall depth to around 75mm-100mm rather than the standard 50mm typically used for artificial lawns that receive light to moderate footfall.
For pet-friendly artificial grass installations, use a higher proportion of granite dust. Due to its drainage capabilities, dog urine will drain through to the subsoil quicker and help to avoid lingering odours.
Can you use sharp sand instead?
Sharp sand has been used to lay artificial grass for decades. Some artificial grass installers still recommend it today because it is more cost-effective than granite.
It should be noted that sharp sand should be used when laying an artificial lawn. You can’t use standard ‘soft’ sand because it doesn’t have the solidity you need to maintain an even surface.
Sharp sand has larger grains so it’s coarser and stronger. It’s also highly permeable and excellent for enhancing the irrigation system of your fake lawn.
The major downside to sand, however, is that it retains moisture and subsequently breeds bacteria. Over time, the sand becomes less stable and starts breaking up which causes the surface to become uneven.
If you have pets or expect the area to be used frequently, using sand as your sub-base will cause your fake lawn to deteriorate and fall out of shape sooner.
On average, artificial grass installations are expected to last between 10 and 20 years. You can’t guarantee this will be the case if you use sand on fake grass installations used to play football.
Sand also provides a favourable environment for plant bulbs to grow. Seeds are stores of energy. To flourish all they need are the right conditions, namely, heat and moisture.
When seeds sprout, they can penetrate sand and will push against the underside of your artificial grass. When this happens, bumps and ridges are noticeable. It’s not a good look, truth be told.
The solution to avoid bulb bumps is to lay a weed barrier beneath the turf installation. However, this is not an option if you have pets because weed barriers are made from a cloth-like fabric that absorbs moisture so will box in pet urine and create an undesirable odour.
Granite or sand: which should you choose?
For the majority of commercial fake grass installation and home artificial turf installation, granite functions better than sand. However, if your artificial lawn is intended for ornamental use and you want to keep installation costs down, sharp sand could be an option.
In truth, granite dust is not much more expensive than sharp sand – only an extra couple of pounds per ton.
Artificial lawns are an investment that you want to last for the maximum duration of its lifespan. If you lay synthetic turf over an unreliable sub-base, you will not get value for money.
How deep should the sub-base be?
Depth is decided by how the lawn will be used, not by the grass on top of it. These are the build-ups we lay:
| Use | Total depth | Build-up |
|---|---|---|
| Ornamental lawn, light footfall | 50mm | MOT Type 1 with a grano dust blinding |
| Family garden, moderate use | 50–75mm | MOT Type 1 with 25mm grano dust on top |
| Football, heavy or frequent traffic | 75–100mm | 75mm MOT Type 1 + 25mm granite dust |
| Dogs | 50–75mm | Higher proportion of granite dust, no weed membrane |
Two things worth knowing before you compare quotes. A quote that does not say how deep it is digging is not a quote you can compare — the depth is most of the labour and most of the cost. And a weed membrane, which is standard on most installs, is the wrong choice if you have dogs: it is an absorbent fabric, so it holds urine and the smell with it.
Groundwork is what moves the price of an installed lawn far more than the grass does. We publish the real figures from our last 298 quotes in what artificial grass costs to install.
