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Carpenter ants and foam insulation

dfvellone | Posted in General Questions on

With xps foam as perimeter insulation on my slab it’s a constant battle with carpenter ants. I live in dense forest, and though I’ve got an interval between the house and woods that I keep clean, the ants just keep coming every couple years. Suggestions for most effective perimeter treatment? 
Thanks, Daniel

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  1. Expert Member


    I face the same thing here on Vancouver Island. I have concrete patios front and back, a concrete paver walkway to the north, and have separated the garden beds to the south with 1 ft of clear crushed gravel edged with Pt lumber. In the ant season I keep 8 lids from juice bottles filled with Ant-B-Gon spaced along the perimeter. They find them before they get into the house and that seems to be the end of them.

  2. nynick | | #2

    These things got into the ridge of my bunkie when it was initially built and spray foamed and never left. Absolute nightmare of a problem. I ended up removing the knotty pine ceiling to get to the nest and quite honestly, I still don't think I got them all.

    They say you need to find the main nest, which is apart from the structure, in a tree trunk or something. But I like Malcom's approach. Inside the house we use Borax powder and sugar.

  3. Expert Member
    BILL WICHERS | | #3

    You can use the borate treatments as you put things together to help keep things under control. There are also ant baits that can help (I use a product from Terro), since the ants take the bait back to their nest and that kills more of them. I don't think there is any 100% effective way to deal with them though -- they will keep coming back if there is something "interesting" to them. Try to keep stuff dry as much as possible, and use a borate treatment, and that's probably about the best two things you can do as a preventative measure.


    1. dfvellone | | #4

      The problem is that the foam on the edge of the slab is irresistible to them. Even though I have deep overhangs and the grade slopes sharply away, it’s inevitable that it gets damp this time of year here in soggy upstate NY, and to them it feels a lot like damp, rotten wood. I tried the bait method a couple years ago when they’d moved into the foam on my 1st floor roof deck and though they sampled it a bit, they never really took to it. I’ve read that they’re fussy and baiting them is difficult. If this foundation foam is going to be a constant attraction I suppose I’ll have to use a regular treatment that will kill them in that location. I’m wondering if excavating and exposing the foam and covering it with some kind of membrane might help.

      1. Expert Member
        BILL WICHERS | | #5

        You could cover the foam with stainless mesh, which is like beefy window screen. I'd normally suggest the fiberglass mesh, but if the ants really want in, they'll eventually be able to chew threw the fiberglass stuff. I'd try a heavy borate treatment on the exposed edge of the foam first though. Try to find a borate treatment that can penetrate, a liquid, instead of just sitting on the surface. If you could get the stuff to get into the material a bit, that might work better.

        If you go with mesh, you need to get it wrapped around the top and down both sides of the foam far enough that the ants won't just go around it, Maginot-line style.


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