MOT Type 1 vs Granite/Limestone Chippings: What’s Best for an Artificial Lawn Sub-Base?

MOT Type 1 vs Granite/Limestone Chippings: What’s Best for an Artificial Lawn Sub-Base?


A key part of any artificial lawn installation is the sub-base.

Without a strong foundation your fake turf will likely fail, so before you commence work, it’s important to consider the best type of sub-base to suit your needs.

When it comes to installing the sub-base for an artificial lawn where you are replacing an existing grass area, you typically have two different types of sub-base aggregate to choose from: MOT Type 1 and granite/limestone chippings.

To help you make an informed decision, we’ve put together this guide to explain the differences between MOT Type 1 and granite/limestone chippings and what those differences mean, in terms of installing artificial grass.

There are some pros and cons of each type of aggregate that you should be aware of before embarking on an installation.

So in our latest article, we’re going to be looking, in depth, at these pros and cons to help you decide on the best type of sub-base to use for your own artificial grass installation.

Let’s begin by looking at exactly what these two different types of sub-base material consist of.



What is MOT Type 1?

MOT Type 1

MOT Type 1

MOT Type 1, or just ‘Type 1’ as it’s most commonly known, is a type of aggregate that is typically used as a sub-base material for a variety of applications.

It usually consists of crushed limestone or granite, but can also consist of crushed concrete.

The particle sizes typically range from 40mm down to dust, creating an aggregate that can be firmly compacted to form a strong sub-base with excellent load-bearing qualities.

Type 1 is typically used to construct roads, driveways, patios and paths, and can also be used to form the sub-base for artificial lawns.

MOT stands for ‘Ministry of Transport’, which is now, in fact, known as the Department of Transport (DOT); however, Type 1 is still commonly referred to as ‘MOT’ Type 1.

It was originally referred to as MOT Type 1 as the aggregate complied with the Specification for Highway Works set out by the Ministry of Transport.

Nowadays, in order for an aggregate to be classed as ‘Type 1’, it must comply with the Department of Transport Specification for Highway Works, clause 803 (SHW 803).



What are Granite/Limestone Chippings?


granite chippings

Granite Chippings

Granite or limestone chippings are essentially MOT Type 1 that has been passed through a sieve, to filter out chippings of the required size.

As MOT Type 1 particle sizes range from 40mm down to dust, anything from 40mm and smaller can be extracted from the aggregate.

Granite or limestone chippings are available in various sizes. Our testing has indicated that the best particle size to use when installing a sub-base for an artificial lawn is 20mm.

Once compacted using a vibrating plate compactor, these chippings can be used as a sub-base material when installing an artificial lawn.



Which is the Best Type of Sub-Base to Use?


Whether you should use Type 1 or granite or limestone chippings really depends upon your needs.

It is true that MOT Type 1 does offer a greater level of compaction and, therefore, will provide a higher strength sub-base material.

However, the downside to using MOT Type 1 is the fact that it is technically not a permeable sub-base material.

This means that little, if any, water will pass through MOT Type 1, and what does pass through will filter through at a very a slow rate.

Granite or limestone chippings, on the other hand, offer a very fast-draining sub-base.

Even after this type of aggregate has been fully compacted, there are still tiny holes within the base material that allow water to pass through very quickly.

The downside to this, however, is that without the smaller particles being present, the level of compaction is not as great as it is with MOT Type 1.



Use Type 1 for Heavily Trafficked & Commercial Areas


compacted type 1

Compacted Type 1

Due to the increased load-bearing capacity of MOT Type 1 over granite or limestone chippings, we would recommend using MOT Type 1 for artificial lawns that will receive heavy, frequent foot traffic.

By this, we mean commercial areas and not applications such as the front or rear garden of a domestic property.

Commercial applications and high footfall areas will benefit more from having an MOT Type 1 sub-base as it will provide a stronger base than granite or limestone chippings.

We would also recommend increasing the overall depth to somewhere between 75mm–100mm of MOT Type 1, rather than the standard 50mm recommended for domestic applications.

It is extremely important to remember, though, that as Type 1 is not a permeable sub-base material, you’ll need to design the lawn with a slight gradient, to prevent standing water.

This gradient should be sufficient to allow the water to run off the artificial lawn and into a drainage system or area that will allow rainfall to return back to the water table.



Use Granite or Limestone Chippings if You Have Pets or Drainage Issues


compacted granite chipping sub-base

Granite Chipping Sub-Base

Due to its inherent drainage capabilities, if you have pets or existing drainage issues in your garden, we would highly recommend that you use granite or limestone chippings as a sub-base material.

The free-draining nature of the aggregate will allow rainfall, as well as dog urine, to quickly drain through the turf and down to the sub-grade (that is, the earth) that lies below the sub-base material.

Using MOT Type 1 when you have a dog can potentially cause issues with nasty odours. This can often be due to urine lying stagnant, directly underneath the turf, as it is unable to quickly drain through the sub-base material.

As a side note, it can also be caused by the installation of a weed membrane, which can absorb moisture, directly below the turf. Again, this can trap nasty odours and, therefore, in this instance, we also advise against the installation of weed membrane directly below the turf.

If you have existing drainage issues within your garden, using granite or limestone chippings is a wise move.

Installing a sub-base using MOT Type 1 would mean designing a fall into the lawn, to allow surface water to drain off the grass – but this would direct an even greater amount of water to an area that is already struggling to drain sufficiently, thereby exacerbating the problem.

Installing a granite or limestone chippings base is effectively like installing a 50mm deep soakaway across your entire lawn area. It will have the capacity to hold water below the surface of your lawn, effectively storing rainfall to allow slower infiltration back into the water table, without creating standing surface water.

In many instances, this greatly improves existing drainage issues; it makes installing an artificial lawn a big advantage for gardens with poor drainage.



Don’t Forget to Install a Laying Course, Too


Granite Dust Laying Course

Granite Dust Laying Course

Of course, once the sub-base has been installed, you’ll need to install a laying course prior to fitting your turf.

This should consist of granite or limestone dust, levelled and compacted to a depth of 25mm.

This provides a flat surface on which to lay out your turf.

You should not place your fake grass directly upon the sub-base material as it will not provide a flat enough surface, with the likely result being an uneven artificial lawn.

For further information, please see our guide, ‘Everything You Need to Know About Installing a Laying Course for an Artificial Lawn’.





neograss artificial grass aberdeen

Ensuring you have an adequate foundation in place prior to fitting your fake turf is vital for long-lasting, high-performing turf.

You can have the best artificial grass in the world, but if you haven’t undertaken sufficient groundworks, your artificial lawn will not stand the test of time.

Whether you should use MOT Type 1 or granite or limestone chippings really depends upon your needs.

Granite or limestone chippings are suitable for all types of domestic application and we highly recommend using this type of base if you have pets or existing drainage issues in your garden.

However, for commercial areas, we would recommend installing MOT Type 1, due to the additional load-bearing capacity it offers.

You will, however, need to ensure that there is enough of a fall to allow surface water to run off the lawn and into a drain or area capable of withstanding the additional surface water runoff.

For further information on sub-base materials, please see our handy guide, ‘Everything You Need to Know About Installing a Sub-Base for an Artificial Lawn’.

If you’d like to leave your installation to the pros, then why not contact your nearest NeoGrass Approved Installer today for your free quotation? An approved installer will have the necessary knowledge and experience to advise upon the best type of installation to suit your individual needs.

Do you have any questions or comments regarding the sub-base materials used in artificial lawn installation? If so, please leave them in the comments section below, as we love to hear your thoughts and would be happy to answer any questions you may have.



29 Responses to “MOT Type 1 vs Granite/Limestone Chippings: What’s Best for an Artificial Lawn Sub-Base?”

  1. Neo Grass

    Hi Stuart,
    As long as the gravel is 20mm and it is suitable for compaction then this should be fine. It’s worth checking with the manufacturer that it is suitable to have a “whacker plate” applied to it.
    The limestone dust is fine for the final layer.

  2. If a 20mm stone chipping base is used. And topped with granite dust. Will the granite dust eventually wash away through the small gaps in the subbase. Should a membrane be placed ontop of the subbase before the grano?

    • Neo Grass

      Hi Jay,
      As long as the chipping base has been thoroughly compacted then the granite dust should hold well enough.
      After you have applied the granite dust it is a good idea to apply a fine mist of water before compacting in order for it set better.
      Kind regards,

  3. If I have pets do I lay a weed membrane on the very bottom too?
    I understand i dont put it directly below the artificial grass but do I still require it below the 1st 20mm limestone chippings?

  4. Morning
    Two part question, can i lay my weed membrane down first before i lay my sub state and secondly can i lay sand on top of granit stone for i lay my fake grass

  5. Hi, I’m about to order some artificial grass and I have a pet dog, can you please provide me the correct step by step process and type of materials you recommend using for this please?

  6. Sunil Sharma

    Hi, Really helpful article. If I have a pet and I am using granite/limestone. I am concerned about weeds etc, so I was planning on doing the following:
    Lay granite/limestone sub base
    Lay membrane
    Lay sharp sand
    Lay artificial grass

    I want to avoid bad dog odours but also I want to avoid any weed coming through.

    Can you advise?

    Many thanks

    • Neo Grass

      Hi Sunil,
      As you have a dog then the first thing you need to do is lay the weed membrane right at the bottom of the area you have dug out.
      Then comes a minimum of 50mm MOT Type 1 or Limestone Chippings followed by a minimum of 25mm of the Granite Dust or Limestone Dust.
      You don’t put a further layer of weed membrane on before the grass.
      Please see our full guide here
      Kind regards,

  7. Ben Bracken

    Hi, I’m planning to lay a circle of artificial grass with a brick edge around it, and have a 14ft pool on top of it during the summer. Would 50mm of limestone chippings and 25mm of granite dust still be suitable for this setup, and would I be able to sit the surrounding bricks on the same limestone/granite base – or would they require a different base?
    Thanks in advance for your help.

    • Neo Grass

      Hi Ben,
      Ideally it would be best to build up the sub base a little bit more just to give it a bit more stability, but don’t increase the depth of the dust.
      When it comes to the surrounding bricks we would think that you would need to fix these properly with a cement base.
      Kind regards,

  8. Richard

    Hi, I’ve been following your guides to install artificial grass, they’ve been a huge help and I have looked at many, so thank you.
    I had my grano dust delivered today, they only had 0-4mm available, however I can’t see any dust, just a bag full of what looks like 4mm stone/grit, does this sound right? Apologies I’ve never used/seen granite dust to compare.
    Thanks for any help.

  9. Good evening, I have a dog to ordered lime stone chippings to lay sub base theses chipping are 20/5 will this be ok at a 50mm depth the 25mm of Grano dust I’m hoping this will still provide good enough drainage as I have a pet dog and too late to change chippings now, many thanks

    • Hi Kevin,
      If your area you are laying the grass on is prone to waterlogging then a 20mm Limestone Chipping sub base is a good idea, followed by the 25mm of Granite Dust.
      If the area generally drains fairly well then a standard MOT Type 1 sub base should be sufficient.
      Kind regards,

  10. Will Brealey

    Hi Wendy

    We have a client with a poorly draining clay rear garden so was thinking of a 100mm sub base of 20mm clean chippings. When laying the sand/grano on top, what is to stop these materials washing out into the sub base, though?

  11. Hi, If I kill off my grass with round up, would it be ok to lay a membrane and subase on top of the soil without digging it up? The drainage is decent. If yes would there be a preference between type 1 or granite 20mm. Many thanks.

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