Silver Bullet Pest ControlYou foamed the gap under the sink, and two weeks later there's a neat little tunnel through it. Expanding spray foam is great at filling space — and terrible at stopping a mouse on its own. Here's how to use foam the right way, what to put behind it, and when sealing is a job for a pro.
4.9 stars on Google • NJ License 90568B • 15+ years • Based in Garfield, NJ • Hablamos español
Text a photo of the gap (with a coin for scale) to 973-510-2585 and we'll tell you what to seal it with.
No — spray foam does not stop mice by itself, because cured expanding foam is soft enough for mice to chew through, often within days. Foam works only as a filler that holds a chew-proof material in place, such as copper mesh, steel wool, hardware cloth, sheet metal or mortar. For gaps that matter, pack the metal in first, then foam over it. Silver Bullet Pest Control (NJ License 90568B) seals homes against mice across Bergen, Passaic, Essex and Hudson counties — call or text 973-510-2585.
Mouse teeth never stop growing, and mice gnaw constantly to keep them worn down. Anything softer than their teeth — wood, plastic, rubber, drywall, caulk, insulation — is something they can get through if there's a reason to. Cured spray foam is light, airy and easy to bite into, so it's no real barrier.
It gets worse: a mouse doesn't have to chew a whole new hole. It only has to widen the edge of the old one. If there's warm air, the smell of food or the scent trail of other mice coming through the gap, it will work at the foam until it's through. We regularly find foam-filled pipe holes with a clean, mouse-sized tunnel right through the middle.
A mouse can squeeze through a gap about the width of a pencil, and a young rat through a hole about the size of a quarter. That's why small gaps matter as much as big ones.
What about "pest-block" foam? Some foams are sold specifically for pests and are made to be less appealing to chew. They're better than plain foam, but a determined mouse can still work through them. We treat them the same way: fine as a cover, not as the only barrier.
| Material | Stops mice? | Best use | Watch out for |
|---|---|---|---|
| Expanding spray foam | No, not alone | Filler and cover over metal; draft sealing | Mice chew through it; breaks down in sun |
| Steel wool | Yes, short term | Stuffing small gaps behind foam or caulk | Rusts outdoors and in damp basements, can be pulled loose |
| Copper mesh | Yes | Stuffing gaps around pipes and wires, inside or out | Must be packed tightly; still needs a cover |
| Hardware cloth (1/4" metal mesh) | Yes | Vents, crawlspace openings, larger holes | Needs secure fastening on all edges |
| Sheet metal / metal flashing | Yes | Gnawed corners, door bottoms, garage door edges, larger openings | Sharp edges; needs proper cutting and fastening |
| Mortar, cement or concrete patch | Yes | Foundation cracks, gaps in brick or block | Needs a clean, solid surface |
| Caulk (silicone or acrylic) | No, not alone | Thin cracks and finishing over metal | Chewable; only a cosmetic or draft seal |
| Door sweep (brush or rubber) | Partly | Gaps under exterior and garage doors | Rubber and brush can be chewed; metal-backed is better |
The pattern is simple: metal or masonry does the stopping; foam and caulk do the finishing.
Look for droppings, grease marks (dark rub marks along edges) or chewing next to the gap. Fix the active routes first.
Vacuum out loose debris, old foam and droppings (wet droppings first and wear gloves). Foam and mortar stick better to clean surfaces.
Stuff copper mesh or steel wool tightly into the gap, deep enough that it can't be pulled out. For bigger holes, cut hardware cloth or sheet metal to cover the opening.
Use foam to fill the space around the metal and lock it in place. Don't overfill — foam keeps expanding. Trim it flush once cured.
Look for new droppings or chewing near the patch. If mice are still active, there's another way in — or they were sealed inside.
Outdoors, cover cured foam with paint, caulk or a cover plate. Sunlight breaks plain foam down over time.
The gaps we seal most often — and where foam alone usually fails:
Gas, water and A/C lines pass through the foundation or siding, and the hole is often cut bigger than the pipe. These are classic spots where people foam and mice tunnel back through. Pack copper mesh tight around the pipe, then seal over it.
The rubber seal at the bottom of a garage door gets chewed or worn, and the corners rarely close tight. From the garage, mice move into the house along pipes and the shared wall. Foam won't hold here — it needs a proper seal and metal at the corners.
Older North Jersey homes with block or stone foundations develop cracks and gaps at the sill. Masonry gaps get mortar or concrete patch; vents get hardware cloth. Foam pushed into a foundation crack is just a temporary plug.
Sealing every hole while mice are still living inside can backfire. Trapped mice will chew new exits — sometimes through drywall, cabinets or the foam you just put in — and some die inside the walls, which leads to a bad smell for days or weeks.
The order that works:
If you already have a smell, our dead mouse smell guide explains what to do. For tips on getting traps to work, see best mouse trap bait.
Heard noise in the attic during the day? That's more likely a squirrel than a mouse. Never seal an opening an animal may still be using — see squirrel proofing or call us.
Wear gloves and eye protection, and keep the area ventilated while foam cures. Uncured foam sticks to skin and is hard to remove.
Don't pack ordinary foam against chimneys, flues, furnace vents or hot pipes. Fire-rated products exist for some uses — check the label and your local code.
Don't stuff steel wool into electrical boxes or around live wires. Wiring gaps inside the house are a job for an electrician or a pro.
Don't foam over weep holes or drainage gaps in siding or brick. They're meant to let water out.
| DIY with foam and steel wool | Professional exclusion | |
|---|---|---|
| Finding gaps | The ones you can see | Full inspection inside and out — roofline, foundation, utilities, garage, vents |
| Materials | Foam, steel wool, caulk | Chew-proof materials matched to each gap: mesh, hardware cloth, metal, masonry patch |
| Mice already inside | Often sealed in by mistake | Trapping and sealing in the right order |
| Follow-up | Up to you | Return checks; mouse service includes 90 days of coverage with unlimited free service calls |
| Best for | One or two obvious gaps, no active infestation | Repeat problems, older homes, multi-family buildings, rats |
Most homes have more than one way in. When droppings keep coming back after you've sealed, the missing gap is usually higher (roofline, attic vents) or hidden (behind the dishwasher, inside the garage wall). See our mice and rat exterminator service.
Tell us where you're seeing droppings or chewing and send a photo of the gaps if you can. We'll inspect, explain what's letting the mice in, and give you a free quote.
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Yes. Cured expanding foam is soft, and mice can chew through it easily, often in a few days if there's a reason to get through. Use foam only to cover and hold a chew-proof material like copper mesh, steel wool or hardware cloth.
It's somewhat better because it's made to be less appealing to chew, but it isn't chew-proof. A determined mouse can still work through it. Put metal mesh in the gap first and use the pest foam as the cover, not the barrier.
Copper mesh or steel wool packed tightly for small gaps, hardware cloth or sheet metal for larger openings, and mortar or concrete patch for foundation cracks. Then seal over the top with foam or caulk to lock it in and block drafts.
Copper mesh is usually better for long-term sealing because it doesn't rust and is easier to pack tightly. Steel wool works but rusts outdoors and in damp basements, leaving stains and eventually loosening. Both need a cover of foam or caulk.
A mouse can fit through a gap about the width of a pencil, and a young rat through one about the size of a quarter. That's why gaps around pipes, under doors and at garage door corners all need sealing, not just the big holes.
Not all at once. Trap the mice inside first while you close the main outside entry points, then finish sealing interior gaps once activity stops. Sealing everything at once can trap mice in the walls, where they chew new exits or die and smell.
Usually because there's another way in you haven't found — at the roofline, attic vents, garage door corners or behind appliances — or because the material used was chewable. A full inspection inside and out normally finds the missing gap.
No. Rats chew even harder than mice and get through foam quickly. Rat entry points need hardware cloth, sheet metal or masonry repair, especially at the foundation, and outdoor rat activity usually needs trapping and burrow work as well.
You can, but plain foam breaks down in sunlight and still won't stop rodents on its own. Pack metal mesh first, foam over it, trim it flush and cover it with paint, caulk or a cover plate so it lasts.
It depends on how many entry points there are, how high they are, the type of building and what materials each gap needs. We give a free quote after an inspection, and mouse service includes 90 days of coverage with unlimited free service calls.
No por sí sola. Los ratones la muerden y la atraviesan. Primero hay que meter malla de cobre o lana de acero en el hueco y luego cubrir con espuma. Llame o mande texto al 973-510-2585 — hablamos español.
Based in Garfield, we seal homes against mice and rats throughout Bergen, Passaic, Essex and Hudson counties.
Updated November 2026 by the Silver Bullet Pest Control team, Garfield, NJ • NJ License 90568B
