I've probably had this hole in my siding for a lot of years - probably since we moved in 20 years ago and before that. Just realized it is where mice have been coming inside. I need to fix hole in sheathing under siding but also need to seal the big gap between the pipe and the siding.

What do I use? Some kind of putty or wrap?

I was thinking of using a plastic mounting block that is designed to fit over siding but the only ones I can find already have holes that don't line up with where I need to put a hole for the pipe.

 

You can get a bar of sealing putty in the electrical or plumbing section of most hardware stores.

 

And don't be tempted to use spray foam. Critters love a well insulated new nest.

Seriously, if there's a big insulation gap in the wall, you can use some foam near the inside wall, then the putty on the exterior as was mentioned.

 

OK, I'll go ask about the putty.

I was thinking maybe spray foam on the inside after sealing the outside. I do have a hole in the sheathing underneath the siding that is in a total inaccessible spot. I can move a tile or two from a suspended ceiling and sort of reach it but it's about a foot below the top of the drywall wall of the finished basement. So I'd like to put something other than putty on the inside. Wish I could get access better to close up the inside but I really don't want to cut out a chunk of drywall.

Hopefully I don't have putty loving mice.

The mouse populations been picking up. Used to be a couple every year, lately it's been a couple every couple weeks. Hopefully this will close the entrance.

 

You can extend the reach of a spray foam can with straws and duct tape or a length of hose. Just get the low expansion stuff or it could bulge your siding.

 

OK.. Done and hopefully mouse proof and will last a long time.

The putty the guy at the hardware store said to use was duct seal putty. I went to Lowes first and talked to the people running the plumbing, electrical, building supplies and paint department and no one had a clue. Turns out they carried the stuff but no one I talked to had the suggestion to use it. Went to Ace hardware and worked my way up through the experienced levels of the staff until we got to someone who knew just what to use.

They also had a form sealant that was designed to block pests - Great Stuff Pestblock. I used that to seal inside hole around the pipe behind the putty. Fortunately I could reach the area to fill it.

Thanks to those that made suggestions.

 

When I've had the opportunity to fix a hole like that I've used the spray foam installed from the outside followed by a nice wrap of steel wool and then electricians putty. The putty holds the foam in and the critters won't touch the steel wool.