Keep Mice Out
Summary: Catching mice is fairly easy. Learning how to keep mice out of your home is more involved. You need to know their habits, what environments they seek and what materials work best to rodent-proof your home.
Often I get questions asking what should be done to catch a mouse, but much less frequently do I get asked how to keep mice out. From a pest management professional's point of view, discovering how the mouse got inside in the first place would be my main mission. Sure, I'm interested in capturing the little rascal before he urinates and leaves his droppings all over my pantry items, but I know, again, from a professional point of view, that catching a mouse is a fairly simple task which can be done, in most cases, overnight.
I want to make sure that once I have eliminated the intruder, its relatives do not come calling. So, knowing the habits of the house mouse or field mouse is very important to gaining the upper hand in learning how to keep mice out.
The first thing is to closely examine the exterior of your home for entry points. Mice are great climbers, so you need to look high and low. Inspect any place where pipes or conduits come through a wall. Electrical lines, plumbing fixtures, air conditioning conduits, hose bibs and clothes dryer vents should all be totally sealed around their edges. It only takes a hole the size of a dime for a mouse to gain entry. That is only about one-half inch, but that is all it needs to squeeze its head through. The rest of its body can elongate itself and wiggle its way inside. I like a product called Xcluder for sealing up holes. It's inexpensive and very easy to use.
Most often we find mice get inside by getting under worn or missing garage door thresholds. New thresholds must be installed every few years to keep seals tight. Make sure the seals go all the way across the door to include edges. Same for pedestrian doors. If you can see light streaming under the door you can assume that the door will not stop a mouse. Hold a dime on its edge and see if you can hold it upright under the door threshold. Smart Park has a kit that includes everything you need to replace the garage threshold.
Mice love the cover of tall grass along foundation walls. You might think having nice, lush grass along the foundation wall looks good, but the negative aspect is that it gives mice the cover they seek. Eliminating vegetation along walls is one of the things we require of our commercial customers. Homeowners may be less willing to have a uniform bare strip running along their foundation walls, but, at the very least, keep this strip cut very low. Behind the cover of tall grass, mice can gnaw on lose or missing motor joints and discover an entryway into your house. Roundup herbicide does a nice job of knocking down unwanted vegetation along foundation walls.
Be sure to check joints where sidewalks meet the foundation of the house. Old or worn away joint filler can leave cavities that may provide access under slabs or expansion joints leading under slabs. If a mouse can get under a slab and burrow, it may eventually find where toilet plumbing comes up through the slab into your home. Replacement joint fillers can be made of everything from rigid board impregnated with a blend of asphalts to cork fiber to rubber and more. I don't care what you use, as long as there is something filling that expansion joint.
As for the holes on the outside of the house I suggest using a quick setting concrete patch using a product like Quikrete. If the hole is meant to allow the passage of air you don't want to seal it, but you can fill it with the Xcluder stainless steel wool product I previously mentioned. Regular steel wool eventually rusts once wet and it is not recommended to fill these holes. You can also use hardware cloth to cover holes. Hardware cloth, which is not cloth at all, but rather a mesh of galvanized metal, comes in a roll and costs about $8.00 for a 3' x 4' sheet. You need a sheet metal cutter to cut it, but it is a very inexpensive way to seal up holes and rodents cannot chew through it.
Follow these suggestions and you will do a pretty good job of securing your castle from invading rodents.