Rats can chew through soft or poorly cured concrete, but they cannot gnaw through solid, fully cured concrete. The distinction matters because many homes have both types, and rats are experts at finding the weaker spots.
Why It Depends on the Concrete
A rat’s incisors rank about 5.5 on the Mohs hardness scale, which makes them harder than copper, iron, and even human tooth enamel. Those teeth grow continuously throughout the rat’s life, so gnawing isn’t optional. Rats must chew on hard surfaces to keep their incisors worn down, and they’ll test just about anything. The practical rule: a rat can chew through anything softer than its teeth.
Fully cured, solid concrete and stone sit above that threshold. A well-poured concrete slab or foundation wall is effectively impervious to rat teeth. But concrete that wasn’t mixed or cured properly, thin concrete block, or concrete that has started to deteriorate with age is a different story. Rats can and do gnaw through soft concrete, crumbling mortar joints, and low-quality concrete block.
Cracks Are the Real Problem
Even when concrete itself is too hard to chew, rats don’t need to bore through a solid wall from scratch. They look for existing weaknesses: hairline cracks, gaps around pipes, deteriorating mortar between bricks, or spots where concrete has spalled from freeze-thaw cycles. Once a rat finds a small crack in a concrete surface, it can widen that opening over time into a hole large enough to squeeze through. A rat only needs a gap about the size of a quarter to fit its body through.
Brick-and-mortar construction is especially vulnerable. Mortar is softer than concrete and degrades faster. Rats can turn a small crack in the mortar surrounding a chimney or foundation into a large opening, eventually causing bricks to loosen and fall apart. If you’re seeing crumbling mortar in your foundation or along a chimney, that’s a potential entry point worth sealing.
What Rats Can and Cannot Chew Through
Concrete gets the most attention, but rats work through a surprisingly long list of building materials:
- Wood: Baseboards, structural beams, cabinets, furniture, and wall framing are all fair game.
- PVC piping: Rats chew through plumbing pipes, HVAC ducts, and drainage lines.
- Brick: Soft brick and mortar joints on exteriors, driveways, and patios can be gnawed through over time.
- Aluminum sheeting: Thin aluminum is no barrier.
- Rubber and vinyl: Weatherstripping, gaskets, and vinyl siding offer little resistance.
- Lead: Found in older homes’ paint and pipes, lead is soft enough for rats to chew.
Materials rats cannot get through include steel, iron, and solid cured concrete or stone. Steel sinks, steel beams, iron sewer pipes, and steel-mesh hardware cloth are all effective barriers. This is why pest-proofing guides recommend steel wool or metal flashing for sealing entry points rather than foam, wood, or plastic.
How Rats Generate So Much Force
Rat bite force scales predictably with body size. Research measuring bite force across rodent species found that a woodrat (about 320 grams) generates roughly 30 newtons of force at the incisors, while smaller species like deer mice produce around 10 newtons. Common Norway rats and roof rats, the species most likely invading homes, fall in a similar range to woodrats or slightly above, depending on size. That force concentrated on the narrow, chisel-shaped edge of a continuously sharpened incisor is enough to score and chip away at surprisingly hard materials over repeated gnawing sessions.
The key isn’t one powerful bite. Rats gnaw in rapid, repetitive strokes, gradually wearing material away like a file. A single session might barely leave a mark on a hard surface, but rats are persistent. They’ll return to the same spot night after night, and over weeks they can open a passage through materials that seem impenetrable at first glance.
Protecting Concrete Entry Points
If you’re trying to keep rats out, the condition of your concrete matters more than whether you have concrete at all. Inspect foundation walls, garage floors, and basement slabs for cracks, gaps around utility penetrations, and crumbling mortar. Any opening larger than half an inch is worth repairing.
For patching, use a high-quality concrete mix and let it cure fully before considering the area sealed. Stuffing steel wool into gaps before patching adds an extra layer of protection, since rats won’t chew through steel. Hardware cloth (steel mesh with small openings) is effective for covering larger vents or drain openings where you can’t pour solid concrete. Avoid filling gaps with expanding foam alone. Rats chew through foam in minutes.
Where mortar joints have deteriorated, repointing with fresh mortar and monitoring for new cracks is the most reliable long-term fix. Pay special attention to where different materials meet: pipe penetrations through foundation walls, the junction between a concrete slab and a brick wall, and any spot where settling has opened a gap.