Termites cannot eat concrete. Their digestive systems are built to break down cellulose, the organic compound found in plant cell walls, which means they feed on wood, paper, cardboard, and similar materials. Concrete is made of cement, water, and aggregite like sand or crushed stone, offering zero nutritional value to a termite. But while termites can’t eat or digest concrete, they are remarkably good at finding ways around it, and that distinction matters for every homeowner with a concrete foundation.
Why Concrete Is Off the Menu
Termite mandibles are impressively strong for their size. They can shear through dense oak and pine with ease. But cured concrete is a different material entirely. A termite attempting to bite through a solid concrete slab would break its jaw before making any progress. The hardness mismatch is simply too great.
Even if termites could somehow chip away at concrete, there would be no biological payoff. Termites depend on specialized gut microorganisms to convert cellulose into usable energy. Concrete contains nothing those microorganisms can process. Without a food reward, there’s no evolutionary reason for termites to develop the ability to bore through it.
How Termites Get Through Concrete Anyway
Here’s the problem: termites don’t need to eat concrete to get past it. Concrete slabs crack as they cure and settle. They shrink away from foundation walls over time. Every concrete foundation develops hairline fractures, expansion joints, and gaps around plumbing penetrations, bath traps, and utility lines. Subterranean termites, which live in soil colonies and travel upward to reach wood, only need a tiny opening to squeeze through.
Physical termite barriers give a sense of just how small these insects are. Stainless steel mesh designed to block termites uses apertures no larger than 0.66 mm by 0.45 mm, roughly the size of a sand grain. If a gap in your foundation is wider than that, termites can potentially pass through it. Sand barriers used beneath slabs work on the same principle: particles are sized between about 1.2 mm and 2.8 mm depending on the termite species, chosen so the grains are too large for termites to move but too small for them to squeeze between.
Common entry points in concrete slab homes include cracks where the slab meets the foundation wall, construction joints, plumbing penetrations, and any spot where the concrete has pulled away from an adjacent surface.
Mud Tubes: The Telltale Sign
Because termites can’t travel through concrete, they go over it. Subterranean termites build pencil-width shelter tubes out of soil, saliva, and waste, and these tubes run up foundation walls, support piers, and plumbing pipes to reach the wooden framing above. The tubes protect the colony from open air and predators while creating a sealed highway between the soil and your home’s wood.
You’ll most often spot mud tubes on exterior foundation walls or inside crawl spaces. If you find one, Mississippi State University Extension recommends breaking away a one-inch section and checking back over the next few days. If you see live termites immediately or the tube gets repaired, the infestation is active. Destroying the tubes alone won’t solve the problem. The colony remains underground and will simply find or build another route in.
Hollow Block vs. Poured Concrete
Not all concrete foundations carry the same risk. Poured concrete slabs are relatively solid, so termites are limited to cracks, joints, and penetration points. Hollow concrete block (CMU) foundations are a different story. The hollow cores inside each block create hidden vertical channels that termites can travel through undetected, sometimes reaching the wooden sill plate at the top of the wall without ever being visible from the outside. If you have a block foundation, interior inspections are especially important because evidence of termite activity may not appear on the exterior surface.
Protecting a Concrete Foundation
The most effective termite defense for slab-on-grade homes is a chemical barrier applied to the soil before the concrete is poured. The termiticide goes onto the sub-slab fill material (gravel or crushed stone) at a rate of about one gallon per ten square feet, creating a treated zone that termites won’t cross. A vertical barrier is also established in the soil around all foundation walls, pillars, and chimney bases, typically extending down to at least four feet below grade.
For existing homes, post-construction treatment involves drilling through the slab along cracks and construction joints at 12-inch intervals, then injecting termiticide into the soil beneath. Drilling is also done within six inches of the foundation wall to re-establish the chemical barrier that may have broken down over time. This is standard professional work, not a DIY project, because incomplete coverage leaves gaps the colony will find.
Physical barriers offer a non-chemical option. Stainless steel mesh (grade 304 or 316 wire, minimum 0.18 mm diameter) installed beneath and around the slab creates a permanent obstacle. Properly graded sand barriers work similarly. Both are most practical during new construction, when they can be laid before the slab is poured.
What to Watch For
Termite damage in a concrete slab home often goes unnoticed for years because the insects enter from below, out of sight. Beyond mud tubes on foundation walls, signs include hollow-sounding wood when tapped, buckling or blistering paint on baseboards, small piles of wings near windows (left behind after a swarm), and sagging floors or door frames that no longer close properly. Homes in warm, humid climates face the highest risk, but subterranean termites are found in every U.S. state except Alaska.
Annual inspections of your foundation’s exterior, crawl space, and any exposed concrete surfaces are the simplest way to catch activity early. Pay particular attention to areas where plumbing or wiring enters the slab, expansion joints in garage floors, and anywhere the concrete meets a different material. The cracks you’re looking for are often barely visible, but to a termite colony, they’re an open door.