Best Sub-Base for a Patio in the UK (What Professionals Actually Use)

If your patio sinks, cracks, or goes uneven over time, it’s almost never the slabs at fault.

It’s the sub-base.

Get this part wrong and no amount of pointing, adhesive, or expensive paving will save the job. This guide explains exactly which sub-base to use, how deep it should be, and how professionals build a patio that lasts.

What Is a Sub-Base?

The sub-base is the foundation layer beneath your patio. It:

• Spreads weight evenly

• Prevents movement and sinking

• Allows water to drain

• Protects against frost damage

• Stops slabs cracking

Without a solid sub-base, your patio will eventually fail — no matter how good the paving looks on day one.

The Best Material for a Patio Sub-Base

✅ MOT Type 1 (The Professional Choice)

Ask any experienced groundworker what they use under patios and driveways and the answer will always be the same:

MOT Type 1.

It’s a crushed limestone or granite mixture that locks tightly together when compacted.

Why professionals use it:

• Industrial-strength compaction

• Excellent drainage

• Road-grade durability

• Affordable and widely available

• Suitable for patios and driveways

If you want a patio that stays flat for years, this is what goes underneath it.

Buy your Type 1 Here

⚠️ What NOT to Use

Avoid using:

• Building sand

• Sharp sand alone

• Ballast

• Loose hardcore

• Broken rubble

• Decorative stones

These materials shift, wash out, and cause slabs to sink or rock.

How Deep Should the Sub-Base Be?

The depth depends on the ground you’re working with:

Always compact in layers of no more than 50mm at a time.

Putting it all down in one thick layer weakens the base.

Should You Use a Weed Membrane?

✅ Yes — always.

A quality membrane:

• Stops soil mixing with MOT Type 1

• Improves drainage

• Reduces movement

• Increases lifespan

Lay it directly on compacted ground before installing the sub-base.

Buy your weed membrane here

How Much MOT Type 1 Do You Need?

As a rough guide:

• 1 bulk bag ≈ 0.5m³

• 1m² at 100mm depth = 0.1m³

Estimated quantities:

Always allow a little extra. Running short halfway through ruins compaction.

What Goes On Top of the Sub-Base?

Your bedding layer depends on paving type:

Never lay slabs directly onto Type 1.

Why Patios Fail (And How to Avoid It)

Most failed patios come from:

• No sub-base

• Base too shallow

• Poor compaction

• No membrane

• Incorrect materials

• Rushing the job

If the base is right, the patio will look good for years.

Need Sub-Base Delivered?

UK Building Supplies supplies trade-grade:

• MOT Type 1

• Sharp sand

• Membranes

• Jointing compounds

• Paving and blocks

Nationwide delivery and materials you can rely on.

Final Advice

A patio only lasts as long as its foundations.

Cut corners in the base and it will show.
Do it properly once — and you won’t be doing it again.