Mouse Problem

Summary: The first step in resolving a mouse problem is to figure out where they are getting in and properly closing those holes. Don't do anything else until you have properly excluded the mice.

Diane; Clarksville, MD asks:

We recently moved into a house that was infested with mice in the attic. We did not know that there were mice in the attic, later we found that they had been using the basement ceiling as a "runway". We hired an exterminator to clean up the attic and the basement. We thought we were done when we started hearing noises again in the attic. We were told that there "stragglers" and just keep trapping them. So far we have trapped two.

We hired another roof inspector since the house inspector completely missed the infestation and we were losing confidence in our exterminator. He believes that the mice are digging into the mulch and going behind the brick facade and entering the attic. They can also enter the basement ceiling from this location. He suggests that we remove the mulch away from the exterior of the house and dig an area ten inches by ten inches, the length of the brick wall, and fill with concrete mixed with glass.

After many contractors and many differing opinions we are still not sure how to proceed. Some told us that they don't believe that the concrete idea is possible, but they will certainly take our money and pour the concrete. Others think that the mice are coming in underneath the cement steps since it appears that our walkway has buckled in places. There may be a hollow space underneath.

We are very confused and not sure hoe to proceed. Thanks.

Ask the Exterminator says:

Whoa! Too many suggestions from too many sources. Everyone slow down and let’s think clearly about what is happening here.
 
The very first rule in rodent control is figure out how the mice are getting inside and close those entryways. Remember that a mouse only needs a hole the size of a dime to squeeze through. As long as it can get its head through, the body will stretch out and follow. So, grab a good flashlight and mirror with an extension handle and start looking for openings. Look high and low. That’s what the mirror is for.

Do not use foam to seal holes. The mice will quickly chew through that stuff. Instead, use quick setting cement and hardware cloth. Any hardware store carries it and it is always stored next to the chicken wire. It comes in rolls and requires a tin snip to cut to size. Be sure to check spaces under the brick siding. Folding over a piece of the hardware cloth and stuffing it into those openings will keep rodents out.
 
Cut tall grass and weeds away from the foundation walls. Fill ground tunnels with pea gravel. The mice cannot dig through the stuff. Make sure mulch is not touching the brick siding. You should be able to see the foundation walls.
 
If the mice are finding a way inside under the steps you need only to go inside and look for an opening and signs of rodent activity along the inside wall, adjacent to the steps. Once you are sure you have closed up ALL holes you can begin to finish off the mice already inside the house.

You did not mention what they are eating inside the house. Pet food? Your food? Mice won’t venture far from their nests (15 to 25 feet max), so if you are seeing mice in different parts of the house you can assume there is more than one nest.

If the attic has insulation you may be looking at removing and replacing it. Mouse urine cannot be effectively removed once they have soiled the insulation. Plus, the insulation gives them lots of places to hide and hinders your trapping efforts.
 
Now, go and read how to properly pre-bait and trap for mice. You can do this by purchasing a dozen inexpensive snap traps. Read http://www.asktheexterminator.com/rodents/Mouse_Trap.shtml plus lots more articles at http://www.asktheexterminator.com/rodents/index.shtml.

Diane responds:

Hardware cloth

The exterminator put mesh over all the external pipes and vents. I did a detailed inspection of the basement from the top of the foundation to the ceiling and there were no holes in the wood behind the insulation, though the insulation had clearly been tunneled through. There was one huge gap (3"x6") between an air duct and the floor board, which did have many mouse droppings near it. Basically, the hole in the floor was cut too big for the duct. I sealed that with a screwed-down piece of sheet metal leaving a 1/4" gap.

We've only ever heard or seen mice in the attic. The attic has had multiple traps in it for several weeks now. Some are without bait, while others are baited with small pieces of potato chips or some of the poison bait our exterminator left. There is also an electronic trap in the attic and one in the garage. They are all mounted, as shown in your videos, perpendicular to the walls. Other than the first night I set them, when we caught the last mouse so far, none have been triggered and there have been no additional noises.

We think the last part of the puzzle is checking and closing off the bottom of the brick-front and filling in the holes the chipmunks dug along the foundation, based on the roof inspector's assessment. Thanks for the tip on the hardware cloth and pea gravel. I'm going to try that before the cement, since it sounds like it will do the job and cost 100 times less. Also thanks for the advice on leaving open foundation below the brick. Our old house in NJ didn't have that, so I assumed it was normal.

Again, thanks for your help.