Why Foam, Caulk, and Steel Wool Alone Will Fail
The most common DIY exclusion mistake is sealing entry points with expanding foam or silicone caulk. Both products are designed for air and water sealing, not for rodent control. Rats chew through expanding foam in days. Mice chew through silicone caulk in weeks. Within a month, the sealed hole is open again, often enlarged.
Steel wool is better but still inadequate on its own. Ordinary steel wool oxidizes quickly in exterior or humid environments, turning to rust and breaking down within a season. Copper wool is the better choice because it does not rust, packs tighter, and holds up to gnawing indefinitely when secured properly.
The professional approach layers materials. Copper wool packs the opening tight. A concrete-backed sealant or hydraulic cement caps the surface. For larger openings, hardware cloth or sheet metal backs the fill. This combination holds for years because rodents cannot get purchase on any single component.