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Physical barriers: mesh, graded stone and slab penetrations

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A physical barrier does not poison anything and does not wear out. It just makes concealed entry impossible, which forces termites into the open.

The idea in one sentence

A physical termite barrier is a material termites can neither chew through nor squeeze through. It goes in at every point where they could otherwise get from the soil into the building unseen. It does not kill them. It removes the hidden route, so any attempt to get in has to happen in the open, as a visible mud tube, where an inspection finds it.

The Victorian Department of Health describes physical barriers as the least-toxic method for new buildings. And that is a large part of their appeal: no chemistry, no renewal cycle, nothing to break down.

The materials

  • Stainless steel mesh. A fine woven mesh with an aperture too small for a termite to pass. It is bonded or clamped around pipes and conduits and run along perimeters and construction joints.
  • Graded stone particles. Crushed rock screened to a size range termites cannot move aside and cannot squeeze between. Laid as a layer under or beside the relevant part of the structure.
  • Metal caps and shields on piers and stumps. The traditional ant cap. Worth being clear about: a cap does not stop termites either. It forces them to build around its lip in the open, where you can see them.
  • A monolithic concrete slab is itself listed by QBCC among the management approaches, because an unbroken slab has no path through it. The word doing the work is unbroken.

Why penetrations are the whole game

A slab is not a sealed surface. Water pipes, waste pipes, electrical conduits and cavity junctions all pass through it, and concrete shrinks away from them as it cures. The resulting gap is millimetres wide, permanently damp, and leads directly from soil to the inside of the building. That is the concealed route, and it is where mesh and collars are installed.

The same logic applies at the perimeter, at construction joints, and at the top of the footing. A physical barrier is not a blanket under the house; it is a set of interventions at specific vulnerable points. And it only protects the points where it was installed.

What defeats a good barrier

Almost always the same thing: bridging. Something built or piled up after the fact that covers the inspection zone the barrier was designed to expose.

  • A garden bed or mulch built above the slab edge.
  • A path, patio or driveway poured against the wall, over the perimeter.
  • Foam or rendered cladding continued down past the barrier line into the soil.
  • A deck, step or planter box hard against the wall.
  • Soil covering weep holes.

Every one of those gives a route past a perfectly good barrier, and none of them look like a mistake at the time. Risk factors goes through them in more detail: it is the cheapest termite work you will ever do.

How to find out what your house has

Open the electrical meter box. The Building Code requires a durable termite management notice in a prominent location, usually there. It records the method used, the date of installation, the life expectancy of any chemical component, and the recommended inspection frequency.

If there is no notice, you do not know what is under the house, and that is worth establishing before you rely on anything. A timber pest inspection will report on the system present and its condition. And whatever it is, it depends on being inspected on schedule. That is not a formality, it is how the barrier does its job.

Frequently asked questions

Do physical barriers stop termites getting in?

They stop concealed entry. Termites can still build a mud tube around the outside of a barrier, and that is by design: the visible tube is what the barrier exists to produce.

Can a physical barrier be retrofitted?

Only partially. Mesh and graded stone are installed at construction, at points that are inaccessible once the building is up. Retrofitting an existing house generally means a chemical barrier or a reticulation system instead.

Does a concrete slab mean I do not need anything else?

No. A slab has penetrations for pipes and conduits, and concrete shrinks away from them. Those gaps are the classic concealed entry point, which is why they are treated specifically.

Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.

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