Choosing the best subbase is crucial for any construction project. Whether you need primary, secondary, or recycled aggregates, knowing which one is best suited can be quite a challenge.

Building aggregates can be used for foundations, paving and a variety of construction projects.

At KCM Waste Management, we have both the expertise and the experience to ensure you are using the right materials at the best prices.

What Exactly is a Subbase?

A subbase is a layer of crushed aggregate which bears the load of paving and provides a strong base for it to be laid onto. Subbases evenly distribute the weight of both the paving and any weight placed onto the paving afterwards.

Your subbase is placed between the soil and your paving slabs. This way it services as a platform for the slabs to be laid.

The interlocking of the different particles within a subbase creates a thin layer. This layer then vastly improves the ground’s ability to carry heavy loads without causing damage.

A good subbase will also provide drainage and prevent ‘ruts’ in your paving, which can commonly be caused by subpar installations and materials. As everyday traffic occurs, such as a car pulling on and off your driveway every morning and night, ‘ruts’ can arise in your paving. This can be avoided by ensuring you are using a good quality subbase which prevents channelisation and settlement.

Do I Need a Subbase?

Not using a subbase for your project can scale down the price. However, saving this money in the short-run will very often create problems for you in the long-run. If vehicles will be trafficking the area, a subbase is definitely advised.

To avoid channelisation (sinking) in your paving, we would recommend using a decent subbase!

You can also usually keep your subbase even if your paving is changed, it may need checking and re-levelling but the subbase itself will be fine to reuse.

Some types of paving and surfacing may not necessarily need a subbase, such as pattern imprinted concrete. However, block paving nearly always does. If you’re unsure which one you are using, just check with your contractor!

Suitable Subbases

Subbases are made up of materials that are load-spreading and have good drainage qualities.

Suitable subbases are most road materials which have been approved by your local Department of Transportation.

The first type of material is unbound which is made up of loose aggregates and do not bond or adhere when compacted. This material naturally interlocks within its own particles. Which means it can also be loosened and removed if necessary.

The second type is bound materials. These use a binder such as bitumen or cement to bind together the particles and then set. Which also means they are a lot harder to remove or loosen.

How to Use A Subbase?

Generally, a subbase should be laid and levelled in a layer no thicker than 150mm.

If the subbase material you choose to use is required to be laid in a layer greater than 150mm, you can lay this in layers to build up to the required depth. Each layer must still be 150mm or less and levelled before the next.

You also need to ensure each layer has been thoroughly compacted to allow for the next layer to be placed correctly and lower the risk of settlement once the area is trafficked. As subbase materials are so good at spreading weight (the main purpose of their use!). It is almost impossible to compact a layer of a greater thickness of 150mm. This is why any materials that need a greater depth must be layered.

Where Do I Purchase the Materials From?

Here at KCM, we provide a diverse range of top-quality aggregates to suit all projects.

If you are unsure which subbase would be best suited, we’d be more than happy to offer our expert knowledge. We can also provide a free no-obligation quote for any material, service, or hire.

To discuss the needs of your project or to get a quote today, please contact our Aggregates Manager, Ian, on 01709 762 267 or email

To read more about our Aggregates and Tipper Hire, please click here.