Underlay for Driveway Floors: What You Actually Need Beneath Concrete or Block Paving

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Driveway Underlay: What Goes Beneath the Surface

  • ✔ MOT Type 1 Sub-Base

    This is the main structural underlay — a compacted layer of crushed stone that spreads weight and prevents movement or sinking over time.
  • ✔ Geotextile Membrane

    Laid underneath MOT Type 1 on soft or clay ground, this fabric prevents the stone from sinking into the soil and keeps the layers separated.
  • ✔ Sharp Sand or Laying Course

    Used for block paving, this is a bedding layer that helps achieve levels. It sits above the sub-base but needs solid compaction underneath.
  • ✔ Damp-Proof Membrane (DPM)

    Only used with concrete pours — a polythene layer that stops moisture rising from the soil into the slab. Crucial if you're sealing or finishing the surface.
  • ✔ Reinforcement Layer

    For concrete driveways, mesh or fibre reinforcement may sit above the underlay to strengthen the slab and prevent cracks.

Underlay Requirements by Driveway Type

Driveway Surface Underlay Needed Notes
Block Paving Geotextile + MOT Type 1 + Sand Must be well-compacted in layers
Concrete Slab Geotextile + MOT Type 1 + DPM Rebar mesh often used above DPM
Resin Bound Gravel Concrete base + DPM (if new) Stable concrete is key for long-term finish
Gravel Driveway Geotextile + MOT Type 1 + Gravel No concrete or slab needed — but compaction is vital

Geotextile Fabric

  • Prevents MOT Type 1 or hardcore from sinking into soft or clay ground.
  • Improves stability of the base over time — especially on poor subsoil.
  • Allows water to drain through while separating layers.

Geotextile Fabric

  • Not a moisture barrier — won’t stop rising damp or groundwater.
  • Must be cut and overlapped correctly or it loses effectiveness.

Damp-Proof Membrane (DPM)

  • Prevents moisture rising into poured concrete from below.
  • Essential if sealing, polishing, or finishing the concrete surface.
  • Available in rolls — easy to lay before concrete pour.

Damp-Proof Membrane (DPM)

  • Doesn’t provide drainage — can trap water if base isn’t prepared well.
  • Not used with block paving or gravel — only for concrete slabs.
🔹 Do I need both geotextile fabric and a damp-proof membrane?
Not usually. Geotextile fabric is used to stabilise the ground under MOT Type 1, especially on soft or wet soil. A damp-proof membrane (DPM) is only needed if you're pouring a concrete driveway and want to stop moisture rising into the slab. You wouldn't use both unless you're combining soft ground with a polished concrete finish.
🔹 Can I skip the underlay if the ground is already firm?
On very well-drained, compacted ground, some people skip geotextile fabric — but it's a risk. Without it, MOT Type 1 can still migrate into the soil over time, causing dips and movement. The fabric layer is cheap insurance against long-term issues and is always recommended for driveways carrying regular loads.
🔹 What underlay is needed for block paving?
Block paving requires a compacted MOT Type 1 sub-base and a layer of sharp sand on top. Geotextile fabric is optional but strongly advised if the subsoil is clay or loose. You don't use a DPM for block paving — only for concrete slabs that need to stay dry underneath.
🔹 Is geotextile fabric the same as a weed membrane?
Not quite. Geotextile fabric used under driveways is usually stronger, heavier, and designed to support load-bearing layers like MOT Type 1. Weed membranes are often thinner and designed for light-duty landscaping use. For driveways, always use woven or non-woven geotextile rated for groundworks.

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