Use copper mesh for gaps outdoors and in damp spots, and steel wool only for dry indoor gaps where you can check it now and then. Steel wool is cheap and rodents dislike chewing it, but it rusts and breaks down, especially near the coast. Copper mesh does not rust, holds its shape and lasts much longer outside. Neither should be used alone: pack it tight and seal over it.
For larger openings like vents and tile ends, neither is the right tool. Use hardware cloth, wire mesh or metal flashing.
How each material works
Both materials stop rodents the same way. Packed tight into a gap, the sharp, springy strands are unpleasant to chew and hard to pull out. Rodents gnaw through wood, foam, plastic and most sealants, but metal mesh stops them.
Steel wool is fine strands of steel, sold in pads. It is cheap and easy to find.
Copper mesh is knitted copper strands, sold in rolls made for pest control. It costs more per foot, but it does not rust, it springs back to fill a gap, and it is easier to cut and shape.
The problem with steel wool
Steel wool rusts when it gets wet. In San Diego, that means near hose bibs, under sinks, around AC condensate lines, at the base of walls that get sprinkler spray, and anywhere near the coast where salt air and marine layer keep surfaces damp. Rusted steel wool crumbles, leaves orange stains on stucco and eventually opens the gap again.
It also sheds small fragments that are hard to clean up, and it can scratch hands. Indoors, in a dry spot behind a stove or inside a cabinet, it can hold up well. Outdoors, plan on it failing.
Why copper mesh holds up better
Copper does not rust. It darkens over time, but it keeps its strength. Rolls of copper mesh made for rodent work can be cut to length, folded and stuffed into gaps of different sizes, and they stay put. That makes it a good fit for:
- Gaps around AC line sets, gas lines and hose bibs
- Gaps at the weep screed along the base of stucco walls
- Pipe openings under sinks
- Gaps around cable and phone lines
- Small cracks at the slab edge in garages
Near the beach in places like Ocean Beach, Pacific Beach, Coronado and La Jolla, it is the better choice for any outdoor gap.
Seal over it
Mesh alone can be pulled out over time. Pack it in tight, with some of the mesh pushed deep into the gap, then seal over the face with an exterior-grade sealant, caulk or mortar patch. Some people use expanding foam to hold mesh in place. Foam alone is not a barrier, since rats and mice chew right through it, but foam over packed mesh works.
The county's hantavirus brochure suggests caulk or expanding foam for small holes and 1/4 inch, 18 to 22 gauge wire mesh for repairs. The county's rat guidance says to seal openings larger than a quarter.
What to use for bigger openings
Mesh pads are for small and irregular gaps. For larger openings, use rigid metal:
- Hardware cloth or wire mesh, screwed or stapled over gable, soffit and foundation vents
- Bird stops or mesh for the open ends of barrel tiles at the eaves
- Metal flashing for gaps at roof joints and fascia
- Door sweeps and rodent-resistant garage door seals
- Sheet metal or mortar for large holes at the slab edge
See how small a hole mice can fit through for where these gaps hide.
Seal at the right time
If rodents are living inside, seal most gaps first, trap until catches stop, then close the last one. Sealing everything at once can trap rodents inside the attic or walls, where they chew new holes or die. See rodent exclusion.
Check your work
Look at sealed spots a week or two later. Fresh gnaw marks, pulled mesh or new droppings nearby mean the spot is still being tested. Repack and reseal. Check again after big changes like new landscaping, a roof repair or an AC replacement, since installers often open new holes.
A quick guide by location
- Under the kitchen or bathroom sink, around pipes: copper mesh, finished with sealant
- Behind the stove or dryer, dry and indoors: steel wool or copper mesh, finished with sealant
- Around AC lines, hose bibs and gas lines outside: copper mesh, finished with exterior sealant
- Weep screed gaps at the base of stucco: copper mesh pressed in, with a sealant bead
- Garage door corners: brush seals or rubber seals made for the door, not mesh
- Vents and tile ends: hardware cloth, wire mesh or bird stops
If you find droppings near a spot you sealed, recheck it first. See garage rodent control for door seals.