Steel Wool vs Copper Mesh: What to Use to Seal Rodent Holes

How small a gap rodents use

The numbers explain why sealing has to be thorough. University of Kentucky pest training says mice can squeeze through openings about the width of a pencil, a quarter inch, and rats through cracks about half an inch. University of California guidance adds that a rat can squeeze under a door with only a half-inch gap, and recommends sealing any opening larger than a quarter inch.

That means the gap around a pipe under the sink, the space at the bottom corner of a garage door and a missing brick mortar joint are all doors.

Steel wool

Steel wool is cheap, easy to find and easy to pack into small gaps. University of California guidance lists steel wool among the materials for sealing rat openings, and notes stainless steel scouring pads make a good temporary plug for mouse holes.

The problem is rust. Plain steel wool breaks down when it stays damp, and once it rusts away, the gap is open again. Rust can also stain brick and siding. It is fine for dry interior spots, like a gap behind a cabinet, and less suited to crawl spaces, exterior walls and plumbing gaps in a humid climate.

Copper mesh

Copper mesh comes in rolls of knitted copper and is made for pest exclusion. It does not rust, it holds its shape when packed, and rodents dislike chewing it the same way they dislike steel wool.

It costs more than steel wool, but it lasts much longer outdoors. For Memphis, where crawl spaces stay damp and exterior gaps catch rain, copper mesh or stainless steel wool is the better choice in most outdoor and under-house spots.

Pack it, then seal it

Mesh alone can be pulled out by a determined rat. Pack it tightly into the gap, leaving no loose ends, then seal over it with a sealant or mortar. Expanding foam is fine as a cover over packed mesh but not on its own. University of California guidance warns that rats chew through plastic, foam, wood and caulk, and lists rubber, vinyl, insulating foam and wood as unsuitable for blocking mouse holes.

When you need something stronger

Mesh is for small gaps. Bigger openings need other materials:

• Vents: galvanized hardware cloth with half-inch or smaller openings, per University of California guidance; avoid chicken wire, which rats pass through
• Chewed fascia or roof returns: sheet metal or aluminum flashing
• Holes in brick or block foundations: mortar or concrete patch
• Gaps under doors: door sweeps and threshold seals
• Garage doors: a new bottom seal and corner seals

See rodent exclusion for what a full sealing job covers.

Openings to leave alone

Some openings need to stay open. Weep holes in brick veneer let water drain; fill them solid and you trap moisture behind the brick. Use vented weep hole inserts that keep mice out and let water through. Foundation and attic vents need screens, not solid covers. Dryer vents need a working flap, not a plug.

Common Memphis gaps and what to use

A quick guide for the openings Memphis homes most often have:

• Gap around a pipe under the kitchen sink: copper mesh packed tight, then sealant
• Gap around AC line set at the outside wall: copper mesh and sealant, or a line set cover
• Missing mortar between bricks: mortar
• Rusted crawl space vent screen: new galvanized hardware cloth or a new vent
• Chewed soffit edge: sheet metal or aluminum flashing
• Gable vent with torn screen: galvanized hardware cloth behind the louvers
• Bottom corners of the garage door: new bottom seal and corner seals
• Gap under an exterior door: door sweep

Roofline work at height is best left to someone with the right ladder and experience.

Checking your work

After sealing, check the spots a few days later. Look for fresh gnaw marks, pulled-out mesh or new droppings nearby. A rodent testing a seal will often chew at the edges. If a seal has been worked on, reinforce it with metal.

Check exterior seals again each fall, since Memphis weather, settling and new rodent pressure can open them up over time.

Seal after trapping

Seal gaps after the rodents inside are trapped out. Sealing them in can push them into living space, or leave them to die in a wall. See best traps, or call to reach a local technician for trapping and sealing together.