The best way to get rid of mice in your home is to eliminate entry points into the house. One of the areas many people neglect is the house foundation. Mice will come through holes as small as a 1/2 inch in diameter. If a mouse gets its head through, the body will follow. The best way to seal up the holes in a house foundation to keep mice out is to identify all the holes first. Once you know where the holes are, sealing them depends on the size of the hole.
Go into your crawl space with a box of toothpicks or wooden matches and look for holes on each foundation wall. Anywhere sunlight shines through is a potential entry for mice. Insert a match or toothpick into small holes so the end of the stick is protruding outside.
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Fill in holes and cracks less than 1/4 inch with silicone caulk and a caulking gun from the outside. Go around the perimeter of the foundation, finding your matches or toothpicks. Pull the stick out of the hole before caulking.
Cut 6 square inches of hardware cloth with a pair of tin snips for holes between 1/4 and 1/2 inch in circumference. Stuff the hardware cloth into the hole so it is below the surface of the foundation. Cover the hardware cloth and hole with caulk. Avoid using standard steel wool as it rusts and deteriorates over time.
Measure holes larger than a ½ inch with a tape measure. Cut squares of hardware cloth 2 inches wider than the hole with the tin snips.
Hold the hardware cloth flat over the hole and apply cement patch over the cloth with a putty knife. Cover the cloth and hole with the cement patch, smoothing the patch with the putty knife.