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Why you should use a Sub-Base when Laying Paving

How to lay a patio sub base

Are you dreading those first signs of your patio pavers shifting? Do the spaces between your paving stones seem to grow before your eyes as weeds take root and flourish? As tempting as it might be to blame poor workmanship, the real culprit could be something underneath those pavers – or more accurately, the lack of it.

Laying patio pavers or any type of paving without the proper base layer is a recipe for future problems. But with the right materials and techniques for constructing a patio sub-base, you can create a long-lasting, stable foundation for your pavement.

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With the insights from this guide, you can feel confident your patio or other paved surface will stand the test of time.

What is a Patio Sub-Base?

A sub-base is a layer of material that is installed underneath paving like patio slabs, pavers, or other types of stone or concrete pavement. The sub-base sits below the bedding layer of sand or mortar and directly above the compacted soil subgrade.

The main purpose of a sub-base is to provide a stable foundation for the paving materials on top. The sub-base helps spread the weight and pressure evenly to prevent shifting, sinking, or cracking of the pavers over time. It also allows for proper drainage below the pavement surface.

An ideal sub-base material is compatible, drainable, and frost-resistant. The most common materials used are either crushed stone or a specific angular gravel known as MOT Type 1. It’s a preferred choice as it is specially engineered to create a solid base. Other good options can include compacted sand, gravel, or recycled concrete blend. The key is using an aggregate that can be packed tightly together without shifting.

Benefits of Using a Sub-Base for your patio

Installing a quality sub-base underneath your paving provides some major advantages that will keep your patio, driveway, or pathway looking pristine for years. Here are some of the key benefits:

  • Prevents shifting and sinking of pavers — the sub-base creates an even, stable layer that distributes weight and pressure. This keeps the paving slabs tightly locked in place over time.
  • Provides a solid foundation — a sturdy sub-base allows the paving to resist cracking or buckling even with heavy use or freeze/thaw cycles.
  • Improves drainageaggregate materials in the sub-base allow water to drain away from the paving surface. This prevents pooling below the pavers which leads to damage.
  • Stops weed growth — with proper drainage and no exposed soil, weeds have nowhere to take hold underneath the paved surface.
  • Allows for easy repairs to be made — it’s easier to remove and replace your pavers later for repairs over a compacted sub-base.
  • Extends the lifespan — quality pavement with a sub-base often lasts for decades rather than years before requiring replacement.

Different Types of Sub-Bases for patio

mot-type-1

There are a few different types of aggregates that can be used to create a sub-base for paving. The most common options include:

  • Hardcore — this recycled rubble material is made up of broken bricks, concrete, and stone. The pieces must be compacted together without voids or gaps.
  • Sand blinding — a layer of coarse sand that is spread over the lower sub-base layer to provide a smooth and level surface.
  • MOT Type 1 — this is a preferred crushed stone aggregate that meets specific grading requirements for particle sizes. MOT Type 1 is an engineered product that creates an excellent sub-base.

MOT Type 1 is considered the highest quality sub-base option for paving projects and there are several reasons for it. First of all, it meets national standards — produced to Britain’s Ministry of Transport (MOT) specifications for particle shape and size distribution. Secondly, it creates a solid base because angular stones interlock tightly when compacted together. Thirdly, MOT Type 1 is a very stable material, as it can resist shifting or sinking under loads, and stands up to freezing and heavy rainfall. With this sub-base, you won’t need to worry about the longevity of your pavement.

Wrong Types of Patio Sub-Bases

Topsoil is bad for patio sub-base

You may think or have heard that materials like sand, topsoil, and low-quality hardcore are great money-saving options. However, in reality, you really should avoid them for sub-base construction. Here’s why:

  1. Sand is too unstable and shifts under pressure, causing pavers to tilt or sink. It also allows weeds to sprout up, which you definitely don’t want to see.
  2. Topsoil is far too soft for this application, it compresses too easily and leads to an uneven base for pavers.
  3. Low-quality hardcore isn’t also an option as it can contain debris and lack angular stones needed for stability.

These inferior materials compromise the integrity of the sub-base. So it’s not worth it even due to the low price. We recommend using only those three types, that were described in the previous section.

How Deep Should My Sub-Base Be?

That’s a great question to ask, but the answer depends on what paving project you are working. Usually, these are the main recommendations for the sub-base depth:

  • Patios and garden paths — minimum of 4 inches (100mm) of compacted sub-base.
  • Driveways and parking areas — minimum of 6 inches (150mm) of compacted sub-base.
  • Heavy duty or commercial projects — 8 inches (200mm) or more may be ideal.

A good practice is to make your sub-base at least twice the thickness of the paving material that will be laid on top. This ensures a stable foundation that will last for decades.

How to Install a Patio Sub-Base

If you want to install a proper patio sub-base on your own then here are the key steps:

  1. Mark out the area and dig down to the proper depth. Remove any topsoil. Dig at least 2 inches deeper than the finished base height for the sub-base layer.
  2. Compact the exposed subgrade with a plate compactor.
  3. Spread an even 3-4 inch layer of MOT Type 1 aggregate over the compacted soil.
  4. Use a compactor to pack down the MOT Type 1 firmly. The stones should interlock tightly with no gaps.
  5. Repeat steps 3-4 to build up compacted layers to your desired sub-base thickness.
  6. Add a 1-2 inch layer of sharp sand over the compacted sub-base and level it smoothly.
  7. For permeable jointing, spread a mortar bed 1-2 inches thick over the sub-base using a mix of 4 parts sharp sand to 1 part cement.
  8. Ensure the finished sub-base slopes away from buildings at a rate of 1/4 inch per foot for proper drainage.
  9. Paving can now be laid directly onto the prepared sub-base. Keep it level and consistent.
  10. Fill joints completely with kiln-dried sand or aggregate.

We know that without a good visualization, it may be hard to understand the full process. That’s why we have put here a video on how to install a patio sub-base by DIY journey

Also for the future, take a look at our post about how to lay garden paving slabs.

Conclusion

When it comes to paving projects, there are a few overlooked things for the sub-base preparation. Skipping on making the foundation layer may seem harmless initially. Yet the shifting pavers, cracks, and sprouting weeds will soon reveal the mistake. Installing sub-base aggregates like MOT Type 1 and making the right depth is worth the effort. It will provide stable support for the pavement, and prevent any problems associated with the repairs. Don’t leave your paving layer’s fate to chance — invest in quality sub-base installation and you’ll reap the benefits for decades to come.

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