Under Fence Plinths — Concrete | Plain, Timberlook & Composite

Concrete Under-Fence Plinths — Seal the Gap, Stop Erosion, Contain Pets

After 50 years of building retaining walls and fencing systems across Australia, the under-fence plinth is one of the most underrated finishing products on any job. A concrete plinth laid at the base of your fence line does what no amount of backfill or gravel can — it permanently seals the gap between the fence and the ground, stopping soil washout, weed intrusion, pet escapes, and the ongoing maintenance headache of a fence that never quite sits flush with the ground.

Our under-fence plinths are pre-stressed reinforced concrete, 50mm thick, Australian-made, and available in three finishes to match your fence style. They're the same product we specify on our own retaining wall and fencing jobs — not a compromise product, not a lightweight alternative.

Product range reviewed and specified by the Retaining Walls Direct trade team. Last updated July 2026.

Choose Your Finish

Not sure which finish to choose? Plain is the most popular — it sits below fence height and is rarely visible once installed. Timberlook suits any job where the plinth face is exposed and you want it to blend with a timber fence aesthetic. Composite is sized specifically for composite fence systems where the 2380mm length matches panel module spacing.

Why Concrete — Not Timber or Plastic?

We've seen timber plinths rot within 3–5 years in reactive clay soils, and plastic alternatives crack under ground movement. Pre-stressed reinforced concrete is the only material that genuinely lasts in Australian ground conditions — it won't rot, warp, crack under normal load, or attract termites. In reactive Class H clay soils (common across Brisbane, Western Sydney, and Melbourne's outer suburbs), concrete is the only sensible choice. It moves with the ground without failing.

• Pre-stressed reinforcement — Steel strand tensioned through the concrete core reduces cracking under load and ground movement, unlike standard unreinforced concrete strips.
• 50mm thickness — Sufficient structural depth to span between fence posts without sagging or cracking under soil pressure.
• Termite-proof — No organic material. No termite risk. No treatment required.
• Zero maintenance — Once installed, concrete plinths require no painting, sealing, or replacement for the life of the fence.
• Australian-made — Manufactured to Australian standards. Not an imported product.

What Problems Does an Under-Fence Plinth Solve?

• Pet containment — Dogs and cats can't dig under or squeeze through a concrete plinth. The most common reason homeowners order these.
• Soil and mulch washout — Stops garden bed soil, mulch, and gravel washing under the fence line during rain events.
• Weed intrusion — Eliminates the gap where weeds grow along the fence base — a persistent maintenance issue on any unsealed fence line.
• Erosion on sloped sites — On sites with any fall, an open fence base allows water to channel under the fence and erode the soil profile. A plinth stops this.
• Reactive clay ground movement — On Class M and H clay sites, the ground moves seasonally. A concrete plinth moves with it without cracking or creating gaps, unlike timber or plastic alternatives.
• Finishing a retaining wall top — Plinths are also used to cap the top of a low retaining wall where a fence sits above, creating a clean transition between wall and fence.

Installation Overview

1. Prepare the fence line — Ensure posts are set and the fence line is established. The plinth sits between posts at ground level.
2. Excavate a shallow trench — Dig 50–100mm deep along the fence line to partially bury the plinth for a flush finish and to prevent it being kicked or shifted.
3. Bed on compacted sand or gravel — Lay a 20–30mm bed of compacted sand or fine gravel for a level, stable base. Do not bed directly on reactive clay without a sand layer.
4. Position the plinth — Slide the plinth between posts. The 2350mm length is designed to span standard 2400mm post centres with clearance for post flanges.
5. Backfill and compact — Backfill both sides and compact lightly. The plinth does not require fixing to posts in most residential applications.

Note: On sloped sites, plinths can be stepped down the slope in increments. Contact our team for advice on stepped plinth installation on sites with significant fall.

Complete Your Fence and Retaining Wall System

Under-fence plinths work as part of a complete fencing and retaining wall system. Browse our related products:

• Concrete Sleepers — 40MPa, 50MPa, and 60MPa retaining wall sleepers in all finishes
• Steel Retaining Wall Posts — H-beam UC and C-channel PFC posts, galvanised
• Hardware, Brackets & Cleats — Fence brackets, post caps, and fixings
• Drainage Kits — Ag pipe, geotextile, and weep holes for retaining walls
• Under-Fence Plinths Collection — Browse all plinth options including city-specific availability

Frequently Asked Questions — Under Fence Plinths

What is an under-fence plinth?
An under-fence plinth is a pre-stressed reinforced concrete strip installed at the base of a fence line to seal the gap between the fence and the ground. It prevents soil washout, weed growth, pet escapes, and erosion. Standard size is 2350×200×50mm.

How long do concrete under-fence plinths last?
Properly installed concrete plinths last the life of the fence — typically 30–50+ years in Australian conditions. Unlike timber (which rots in 3–5 years in clay soils) or plastic (which cracks under UV and ground movement), pre-stressed concrete is unaffected by moisture, termites, or seasonal ground movement.

What is the difference between Plain, Timberlook, and Composite finishes?
Plain has a smooth concrete face — best where the plinth won't be visible or for Colorbond fences. Timberlook has a moulded timber-grain texture on the face — suits timber paling or hardwood fences. Composite is 30mm longer (2380mm) to match composite fence panel module spacing.

Do under-fence plinths need to be fixed to the fence posts?
In most residential applications, no. The plinth sits between posts in a shallow trench and is held in place by backfill and its own weight (approximately 55–60kg per plinth). On exposed or high-wind sites, a construction adhesive bead on the post face can be used for additional security.

Can under-fence plinths be used on sloped sites?
Yes — on sloped sites, plinths are stepped down the slope in increments matching the fall. Each plinth sits level within its bay, with the step occurring at each post. Contact our team for advice on your specific site gradient.

How many plinths do I need?
One plinth per fence bay (post to post). For a standard 2400mm post spacing, one 2350mm plinth fills each bay. Divide your total fence length by 2.4 to get the number of bays, then round up.

Delivery & Trade Pricing

We deliver under-fence plinths Australia-wide via our crane truck and freight network. Plinths are heavy goods — freight is calculated by postcode and quantity. Send your postcode and quantities for a same-day freight quote.

Trade accounts and volume pricing available for builders, landscapers, and fencing contractors. Contact our team to discuss trade pricing on your next project.