Do You Need Mesh in a Concrete Slab? (Explained by Size & Load)

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When You Do Need Mesh in a Concrete Slab

  • ✔ The slab is over 100mm thick

    Once you go beyond 100mm, especially for load-bearing slabs, steel mesh helps control shrinkage and improves crack resistance. It also improves performance during temperature changes or ground movement.
  • ✔ You're building a driveway or vehicle pad

    Any slab that will take vehicle weight — even small cars — should include mesh (or rebar). It spreads the load through the concrete and helps prevent early cracking or wheel-track dips.
  • ✔ You're pouring on clay, soft, or unstable soil

    Soft or shifting ground increases the chance of slab movement. Mesh acts like internal reinforcement that ties everything together when the sub-base can’t fully support the slab long-term.
  • ✔ The slab is large or long without control joints

    Bigger slabs are more prone to cracking due to shrinkage and thermal expansion. If your pour is longer than 3–4m without joints, mesh helps absorb that internal stress.
  • ✔ You’re supporting a garden room, cabin, or hot tub

    Heavy static loads — like buildings or water features — put downward stress on a slab. Steel mesh keeps the concrete from bowing, separating, or developing structural failure over time.

Do You Need Mesh? (By Slab Use)

Slab Use Typical Thickness Mesh Needed? Mesh Type
Small shed base 75–100mm ❌ Optional A142 (if used)
Garden office / cabin 100–125mm ✅ Yes A193 mesh
Driveway (cars) 125–150mm ✅ Strongly A252 mesh or rebar
Concrete path 75–100mm ❌ No None (unless poor soil)
Greenhouse base 75mm ❌ No None
Garden patio slab 75–100mm ❌ No (optional if unstable ground) A142 (if added)

Using Steel Mesh in a Concrete Slab

  • Improves overall tensile strength — especially important for driveways and heavy loads.
  • Reduces shrinkage cracking and long-term structural separation.
  • Helps spread weight more evenly across the slab and sub-base.
  • Offers better performance on poor, soft, or unstable ground.
  • Essential for large, thick, or joint-free slab pours.

Using Steel Mesh in a Concrete Slab

  • Increases material and labour cost — typically £10–£20 extra per m².
  • Requires mesh spacers or chairs to position correctly in the slab depth.
  • Can be overkill for small, light-use slabs like shed bases or patios.
  • Slab must be poured carefully to avoid pushing mesh to the bottom.

Not Using Mesh

  • Faster and easier for small pours — fewer materials to manage.
  • Reduces cost, especially for patios, shed bases, or small paths.
  • Fine for well-compacted sub-bases with good drainage and light loads.

Not Using Mesh

  • Higher risk of shrinkage cracks, especially in large or exposed slabs.
  • Weaker long-term performance under heavy or static loads.
  • No internal reinforcement if the ground shifts or flexes.
  • Harder to control slab movement without joints or fibres.
🔹 What does mesh actually do in a concrete slab?
Steel mesh helps control cracking and adds tensile strength to concrete. It prevents slabs from shifting or separating under load, especially in areas where ground conditions are poor or loads are heavy. It doesn’t stop all cracks, but it keeps them tighter and stops the slab from failing structurally.
🔹 Can I use rebar instead of mesh?
Yes — for some projects, rebar is a better choice. Rebar is typically used for thicker, heavily loaded slabs (like driveways or footings) and is installed in a grid or cage layout. Mesh is quicker and easier for most residential slabs, but rebar may be required for structural concrete or vehicle traffic.
🔹 How high should the mesh sit in the slab?
Mesh should sit in the top third of the slab — not directly on the ground or too close to the surface. Use mesh spacers or chairs to raise it 40–50mm above the sub-base or membrane. This helps it stay in position when concrete is poured and ensures it works as intended.
🔹 Is mesh needed for small slabs like patios or shed bases?
Not always. If the slab is thin (under 100mm), on well-compacted ground, and used for light loads, mesh is usually optional. Many patios and shed bases perform fine without it. But if the ground is soft or the slab spans more than 3m in any direction, mesh is still a smart upgrade.
🔹 Can I use fibre instead of mesh?
Fibres help reduce surface cracking and shrinkage, but they don’t replace mesh when it comes to structural strength. For light-use slabs, fibres might be enough. But for driveways, garden offices, or any slab under load, mesh provides the reinforcement fibres can’t match. Many pros use both for added performance.

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