Termites cannot eat or digest concrete, but they absolutely can get through it. Subterranean termites exploit cracks as small as 1/32 of an inch (about 0.8 mm) to reach the wood inside your home. If you can slide a business card into a crack in your foundation, a termite can walk right through it. The signs they leave behind on concrete surfaces are distinctive once you know what to look for.
Mud Tubes on Foundation Walls
The most recognizable sign of termites around concrete is the presence of mud tubes. These are narrow tunnels made from soil, wood particles, and termite saliva that run vertically up foundation walls, piers, or other concrete surfaces. They are typically about the width of a pencil, though they can range from 1/4 inch to 1 inch in diameter, and they are earth-colored, blending in with the foundation if you’re not looking closely. Active tubes can extend up to 15 feet above ground level when termites are climbing over concrete or metal barriers to reach wood.
Termites build these tubes because they need constant moisture and protection from open air. The tubes act as enclosed highways between their underground colony and the wood they’re feeding on. If you break one open and find it moist inside with live termites moving through it, the infestation is active. Even an empty, dry tube is worth investigating, because termites sometimes abandon one route and build another nearby.
Exploratory tubes look slightly different from the main highways. They tend to be thinner, more fragile, and branch out in multiple directions like tree roots running up a wall. These are scouts searching for new food sources, and spotting them early can catch an infestation before it becomes established.
How to Tell Mud Tubes From Mud Dauber Nests
Not every mud structure on your foundation means termites. Mud dauber wasps also build with mud, and the two are sometimes confused. The differences are straightforward. Termite mud tubes are thin lines that climb vertically from the soil upward along foundation walls. They are made of dark, packed earth and are hollow inside when broken open. Mud dauber nests, by contrast, are clustered cylindrical cells made of lighter-colored mud. They sit in one spot, typically under eaves or in sheltered corners, and do not follow a vertical climbing path. A sealed dauber nest is dry to the touch, while an active termite tube has visible moisture inside.
Where Termites Enter Concrete Slabs
Concrete slabs are not solid barriers. They develop cracks from settling, shrinkage, and temperature changes over time, and they are built with multiple joints and penetrations that create natural entry points. The most common spots where termites get through include:
- Shrinkage cracks: As concrete cures and ages, it often cracks or pulls away from the foundation wall, creating gaps termites can navigate.
- Expansion and construction joints: These are intentional seams in the slab that can separate slightly over time.
- Plumbing penetrations: Pipes that pass through the slab leave small gaps between the concrete and the pipe surface.
- Bath traps: The cutout areas in the slab beneath bathtubs and showers are particularly vulnerable because they combine accessible soil with moisture.
Because these entry points are often hidden beneath flooring, walls, or fixtures, termites can establish a path from the soil to your home’s framing without ever being visible from the outside. This is why checking the exterior foundation for mud tubes matters so much: it may be the only visible evidence of activity happening underneath the slab.
Other Signs to Watch For
Mud tubes are the headline indicator, but a few other clues show up around concrete foundations. Look for small piles of soil or grit accumulating near the base of walls, around plumbing access points, or along the edges where the slab meets the foundation. Termites push excavated material out of their tunnels, and these deposits can appear in places where dirt has no obvious reason to be.
Inside the home, signs that often trace back to slab entry include bubbling or peeling paint near the base of walls, floors that feel soft or springy in spots, and hollow-sounding wood when you tap on baseboards or door frames. Swarmers (winged termites) emerging indoors, especially near windows or light fixtures close to ground level, are a strong indicator that a colony has matured beneath or beside the foundation. Discarded wings left behind after a swarm are easy to spot on windowsills and floors.
How Inspections and Treatment Work
A professional termite inspection around a concrete foundation focuses on the exterior perimeter, looking for mud tubes, cracks, and moisture conditions. Inspectors also check interior walls at ground level, crawl spaces if they exist, and anywhere plumbing or utilities penetrate the slab.
Treatment for termites around concrete slabs typically involves creating a chemical barrier in the soil surrounding and beneath the foundation. Around the exterior, this means digging a narrow trench along the foundation wall, applying termiticide to the soil, backfilling, and treating the backfill. Where concrete porches, walkways, or patios prevent trenching right next to the building, small holes are drilled through the concrete at intervals so termiticide can be injected beneath the surface. The holes are plugged afterward.
For new construction, the standard approach is treating the soil directly beneath the building site with termiticide before the slab is poured, creating a horizontal chemical barrier under the entire foundation. This is applied after plumbing and reinforcement are in place but before any concrete goes down.
Reducing Risk Around Your Foundation
You can make your concrete foundation less inviting to termites with a few practical steps. Keep soil graded so water drains away from the foundation rather than pooling against it, since termites seek moisture. Maintain a gap of several inches between any mulch or landscaping soil and the top of your foundation wall so that mud tubes would have to cross visible concrete before reaching wood. Fix leaking faucets, downspouts, or air conditioning drip lines near the foundation promptly.
Store firewood, lumber, and cardboard well away from the house and off the ground. Seal visible cracks in the foundation with appropriate concrete patching material. While sealing alone won’t stop a determined colony, it eliminates easy entry points and forces termites to build visible mud tubes on the surface, where you’re more likely to spot them during a routine check. Inspecting your foundation perimeter every few months, especially in spring when swarm season begins, is the simplest way to catch activity early.