How Subterranean Termites Enter Through Foundation Cracks

Subterranean termites live in the soil, so the foundation is the first line of defence for a building. They do not eat concrete, but they exploit very small cracks, joints and gaps to move up into the structure. Even narrow openings can be enough.

This guide explains how they get in and what to do about it.

The short answer

Subterranean termites enter buildings through hairline cracks in concrete, expansion and construction joints, gaps around pipes and conduits that pass through the slab or foundation walls, and by building mud tubes over the surface of foundations and walls to bridge from soil to wood. They are very small and can use openings that look insignificant. Prevention combines a chemical barrier in the soil, sealing cracks and penetrations, keeping soil levels below the damp-proof course, and avoiding wood-to-soil contact.

Common entry points

1. Cracks in the slab and foundation walls: Even very thin cracks.
2. Expansion and construction joints: Where concrete sections meet.
3. Pipe and conduit penetrations: Gaps around plumbing and electrical lines through the slab.
4. Plinth and wall bases: Junctions where wall meets floor.
5. Voids in masonry: Hollow blocks and gaps in mortar.
6. Mud tubes over the surface: Termites build covered paths up the outside of foundations.
7. Wood in contact with soil: Door frames, steps and posts.

How they find the way

Termites forage through the soil and detect moisture and food. When they reach a foundation, they search for cracks and joints, then follow them upward. Where there are none, they build mud tubes to cross the surface.

How to reduce the risk

• Have the soil treated with a termiticide barrier before or after construction.
• Seal cracks and joints with suitable materials.
• Close gaps around pipes and conduits.
• Keep soil, mulch and plants below the damp-proof course.
• Avoid wood touching soil, such as wooden steps or posts embedded in ground.
• Maintain drainage so water does not collect near the foundation.
• Check for mud tubes on the plinth regularly.

Inspection tips

1. Walk around the outside of the building and look at the plinth for mud tubes.
2. Check inside at the base of ground-floor walls and around pipes.
3. Look for cracks in floors and along skirting.
4. Note damp areas that may attract termites.

If you find tubes

Do not just scrape them off. Photograph them and book an inspection. Treatment may include soil treatment and drill-and-fill along walls and floors.

When to call a professional

Call whenever you find cracks with termite signs, or mud tubes on the foundation. A specialist can trace the route and design treatment.

Frequently asked questions

Can termites eat through concrete?

They do not eat it. They use cracks and joints.

How small a crack can they use?

Very small. Even hairline cracks can be enough.

Does sealing cracks stop termites?

It helps but does not replace a soil barrier.

How often should I check the plinth?

At least yearly, and after the monsoon.

This guide is part of IPest's complete resource on termite control. For identification help, prevention and treatment options, see our full termite treatment guide for Bangalore.