Artificial Grass Sub-Base – MOT Type 1 v 20mm Stone

What is a sub-base?

When installing artificial grass, one of the most important elements is the foundations. Often overlooked, the foundations create a solid base for which your artificial grass will benefit from for years to come. 

Failing to prepare is preparing to fail, and without the proper prep-work, your artificial grass will eventually follow the lumps and bumps of settling and shifting soil. Thankfully, this is easily avoided with a little bit of digging, a sub-base and a laying course. 

In this article, we are going to discuss the pros and cons of the hotly debated sub-base aggregates. 

MOT Type 1 

Most common is MOT Type 1 – the standard of stone required for highways. It is a crushed 40mm to dust aggregate which compacts really well to form an excellent load bearing sub-base.  

Ideal for below patios and driveways designed to take more weight, it is also suitable and commonly used as part of the foundations for artificial grass too. 

Although its main strength is how well it compacts, this can also be a drawback for some installations – as the compacted base makes it less permeable, causing potential drainage issues.  

20mm Chippings 

20mm Limestone or 20mm Granite chippings are also readily available options commonly used for artificial grass installations. 

The stone is free of finer aggregates and dust, which reduces how well it compacts versus MOT Type 1, but conversely provides better drainage as a result due to having more gaps between the stones even after compaction. 

This makes it particularly more beneficial to gardens where drainage is an issue and for pet owners too as it makes hosing down of the grass easier and reduces the likelihood of odours lingering.  

Which to use? 

If you have or expect drainage issues, or have pets that will frequently use the lawn, then opting for a 20mm limestone or similar ‘clean’ stone to provide additional porosity may be preferred as it can help water to escape more freely, whilst still offering sufficient support as a foundation.

If drainage isn’t an issue and you want the peace of mind of a sub-base which can support heavier traffic, then MOT is a more than suitable option. One handy hint if choosing an MOT sub-base, is to create a slight fall to direct water away to prevent standing water and aid drainage.

Both types of material should be readily available in bulk bags from local builders merchants.