You need to kill the ants first. I would either crawl under the house or trickle Amdro into that crack. Then you can glue a trim piece over it.

I started to use granular poison and gel outside the hole, but I think that the entire building (9 floors, 1950s concrete building) is like "infested" so it seems a nevereding battle since they keep coming back after a while.

If I close it with a simple trim piece they will continue to climb and go under the floor. I need to seal it deeply.

I had ants getting in around the drainage pipes. I sprayed a little WD40 in there and they're never come back. I didn't even need to fill in the gaps around the pipes.

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I'd like to use the spray foam but I read that ants can even create a nest in the foam.

About the cauliking, since the hole is little and there isn't much space, I can't "introduce" in that space a caulking gun, and I'm also worried that caulking, since "it's dense", would simply "close the hole on the surface".

I really need to put something "inside" the hole that can fill it and THEN use caulk to seal the top.

You will never stop them by yourself. I'd still use the Amdro. It's a slow acting bait that will be fed to the queen s who will then stop producing new ants. Good luck.

Years ago I had ants... Having the exterminator come and do their thing helped for a while, but then they were back. Possibly sugar ants. Then I did their program where they came out every 3 months for a year. Mostly they just sprayed around the perimeter those last 3 times (likely nest near the house outside). Haven't seen them back, and it's been 10 years now.

Really hard to get an idea from just the one photo/angle. Any to get at it from under the floor? If it were me (after solving the ants problem), I might cut a piece of wood to fill the gap, and if not other way to attach, use construction glue to give a flat, solid surface. After that's set, you could cut a small piece of molding and nail it to the floor and filler piece.

It'd be a lot easier to say if several pix from different angles.

Remove water and ants go away. It may be a structural problem as from that small blurry pic it appears that the wall doesn’t start on the floor and is somehow hanging there a bit

Great Stuff makes an insect and pest resistant foam, I don’t think it’s specifically to keep ants out, but ants are opportunists…IME… if you make it easier to go somewhere else, they usually do.

The way to fix the 1 cm Hole is to nail a 1x3 on to the bottom of the fixed panel where it meets the floor, like a base mounding. If not wide enough, attach 3/4” 1/4 round to the 1x3

Diatomaceous Earth. Non toxic and works.

Backer rod and Big Stretch caulk

https://youtu.be/THNUuxQc73k

And it will just sit there, waiting, until something comes through, unlike oils and other products that evaporate or soak away.

Don't fill the hole. Caulking over top or a transition but that gap is needed for expansion of the floor.

Use termador or sumari. Both are super potent but slow acting. This will allow the queen to contaminated with it, thus killing the whole colony. This is the stuff pros use for termites and ants. I use them for wasps. They are amazing.

You can literally pixie dust the shit anywhere and everywhere. Make a line in doorways. It’ll help, trust me.

You can caulk that gap, or fill it with really anything. For the ants, I put a ring of diatomaceous earth around the whole house

Get advion gel for ants. Put it around the area where the ants are. Let them eat it and bring it to the nest. If you find any nests around that area outside. Put it near them, too. When it’s not going to rain. Find any source of moisture/water. Eliminate it. Within 1-2 years, the ants are gone.

I paid an exterminator $450 to put the gel down. They told me to buy it on Amazon and do it myself. Best $450 I ever spent. Ants were gone forever. In less than 2 years. Cost $35 for 4 tubes on Amazon. Barely used 1/2 of one tube. Ants Gone.

For me, it was the bathroom window leaking water to outside. Once that was cured. With a shade to keep water off the window. The advion killed the ants.

Can’t help you with anything else.

This is the way.

It is not a poison. It is just an abrasive that cuts up the ant.

Don’t do any of this, if you want to properly stop your infestation have to take a few measures. First follow the ant trails and see where the nests are. Second trim back any vegetation making contact with the home back and remove any hoses or other items that may be touching the home. Third, get an insecticide that the ants cannot sense; Termidor SC, Taurus SC, or Phantom will work. Phantom comes pre-mixed the others (original and generic) don’t and those will need mixed for perimeter spray with a 0.06% dilution. Spray the perimeter of the home with an “SC” spray…do not spray flowers or anything bees interact with…about 2 feet out and two feet up during peak ant movement time. Lastly if you found the nest hit it with Phantom.

Now, you’ve forced the ants to move through the insecticide they cannot sense. If they sense a insecticide the colonies get stressed and can split creating multiple new colonies for you to contended with. In two to three days ALL of the offending ants from the offending colony(ies) will die. The SC products use “fipronil” the same chemical found in frontline for cats/dogs. Members of the colony pick it up as they move over it…then as they go to their near they die and as other colony members touch the dead they die and soon the whole colony and every ant in your house is dead or dying.

Once these guys are dead, fix any holes. If it’s concrete then use hydrating cement or epoxy…if it’s wood just cut a place for you to put new wood and seal it up. You’ll never see another health and in your home again.

Good on the tech for telling you to get it yourself. I would too if my company were fleecing people like that, we charge almost half as much and that's in Los Angeles which isn't a cheap marker for pest control.

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Yeah. He said we charge way too much for this, when you can buy it on Amazon for $35.

If you ever have a new bug problem I can recommend the best product to buy. Feel free to message me.

Thanks! 🙏