Should I use foam or caulk to seal gaps in exterior walls?
Homeowners dealing with pest infestations struggle to choose between materials like foam, caulk, or netting because they are unsure what will actually block the openings in stucco and brick. Without a reliable way to securely close large gaps, pests continue to get inside and leave droppings, rendering temporary fixes ineffective.
What the numbers show
Counted from the threads quoted below. How we count
- The most recent one is from October 2026.
- This comes up 17.4× more often in r/HomeMaintenance than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1using spray foam3 people mentionedDid this help you?
- 2applying caulkDid this help you?
- 3using pool noodles to fill gapsDid this help you?
- 4attaching a velcro screen around the top and sidesDid this help you?
- 5installing an outdoor curtain track with mesh curtainsDid this help you?
- 6using outdoor silicone or double-sided tapeDid this help you?
- 7trying to caulk the exterior of the paneDid this help you?
- 8reglazing the windowsDid this help you?
- 9looking into how the windows were originally sealedDid this help you?
- 10Using Dynaflex 230, extreme stretch, or big stretch sealant, and removing old caulk before applying new material.Did this help you?
- 11ensuring good cavity ventilation through weepholes and the frieseboardDid this help you?
- 12Using caulk to fill gapsDid this help you?
- 13Scraping off bubbling paint and repointing loose bricks with mortarDid this help you?
- 14Using spray foam combined with vinyl siding or wood framing to fill and patch the gaps.Did this help you?
- 15Trying to slide mesh down behind beamsDid this help you?
- 16Removing decking boards closest to the houseDid this help you?
- 17Using insulating foam sprayDid this help you?
- 18Clean out the debris first, then pack it with some flexible outdoor caulk.Did this help you?
- 19Using flexible sealersDid this help you?
- 20Applying expanding foam followed by a sealing beadDid this help you?
- 21Hiring a professional masonDid this help you?
- 22Using polyurethane construction adhesive instead of standard caulkDid this help you?
- 23Using elastic stretching sealantsDid this help you?
- 24Filling the hole with closed cell spray foam and capping it with a cement patching compound.Did this help you?
- 25Covering with rigid foam, spraying around it, and packing with batt insulationDid this help you?
- 26Drilling a hole in the rigid foam and filling the void space with spray foamDid this help you?
- 27Putting rockwool insulation up thereDid this help you?
- 28Slicing the rigid foam into a few layers and stacking themDid this help you?
- 29Using steel wool, foam sealant spray cut with an X-Acto knife, or applying white plaster over cut foam sealant.Did this help you?
- 30Using a polyurethane caulk or concrete/masonry sealant to seal the gap while allowing for seasonal wall shifting.Did this help you?
- 31Using mortar caulk from a tube for small pinholesDid this help you?
- 32Mixing a small batch of Type N mortar to pack into deeper voidsDid this help you?
- 33Using Type O mortar as a safer alternativeDid this help you?
- 34trimming the side off one of the vents so they sit flat and using exterior caulkDid this help you?
- 35Using spray foam with thumb gum or steel wool/copper woolDid this help you?
- 36Adding screws to hold the drywall tighter against the footerDid this help you?
- 37Applying expanding foam into gaps where air entersDid this help you?
- 38Applying caulk or silicone with a filler rodDid this help you?
- 39Using spray foam and cutting off the excessDid this help you?
- 40Leaving openings on the bottom edge for drainageDid this help you?
- 41Using long-handled tools like brooms or snow brushes to reach in and pry out debrisDid this help you?
- 42Flushing out the gap with a pressure washerDid this help you?
- 43Blowing out loose dirt with a leaf blowerDid this help you?
- 44Stuffing the gap with copper mesh or foam backer rod before caulkingDid this help you?
- 45Filling the gap with fine gravelDid this help you?
- 46food barrierDid this help you?
- 47Asking on home improvement forums to verify if contractor work is up to standardDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I don’t know how I didn’t notice this BIG ASS GAP . We’ve not even been here a month.”source ↗
“I am not handy but I am sure this is something I can probably do myself instead of hiring for it: I don’t know anything about it though.”source ↗
“It gets leaves and junk and I would like to fill it. But I want to make sure I’m not missing any reason this would be a bad idea. Also, tips on what to use?”source ↗
“I have several holes in the side of the house I just bought that surround the basement windows. I know they need to be sealed, and was hoping for some advice on how to do this.”source ↗
“I’m finishing my basement on my fairly new house (4 years old) and I wanted to upgrade my rim joist insulation and I’ve already purchased 2in rigid foam. Based on this picture, do I shave off the existing spray foam or trim and fit a smaller piece in the available space?”source ↗
“As I replace my shutters here, I am contemplating filling these holes in the mortar. What should I use here, Type N Mortar or a mortar caulk tube from Lowe’s?”source ↗
“I just purchased a house and new to home maintenance, I am not sure if this this gap between a drain and brick in my backyard need to be sealed to prevent water from going in there or was it left there in purpose?”source ↗
“Looking to fill this gap I noticed along our siding to prevent water intrusion. What material should I use?”source ↗
“awhile back we had a big storm that caused all of the windows that look like this to leak water through the bottom of the pane.”source ↗
“Made the mistake of having the house cleaned by what I now realize was a jabroni with a pressure washer and it went through every window pane he hit.”source ↗
“Clearly the is a huge hole around the pipe and it seems like the obvious choice for how mice are entering my house.”source ↗
“My worry is that I dont want to damage the pipe and I live in a cold climate where i think the pipe would expand/move in the winter/summer temps.”source ↗
“My friend suggested insulted foam sprayer which I have no experience with. I just cant damage the pipe.”source ↗
“There has always been warm air coming in from under my kitchen counter.”source ↗
“I am not sure what to do to stop the warm air coming in.”source ↗
“I’m worried though if I leave it unchecked, mold growth is an inevitability.”source ↗
“Something tells me to caulk. Is that right or should there be a gap.”source ↗
“What’s the best way to close this up now? Foam, caulk or what?”source ↗
“I tried to put up netting, but that didn’t work as they still managed to get in and lay eggs.”source ↗
“The problem is the large gaps on the left and right side of the railing. I think the walls are made of stucco/brick. so I don’t know how to attach the netting there in order to have it “complete sealed”.”source ↗
“I need advice on how to block those holes, or advice on how to attach the netting to the stucco.”source ↗
“Literally at this point I was debating buying pool noodles to fill those gaps, but that would look ridiculous.”source ↗
“I’m just desperate for some help, i’m just tired of the poop everywhere”source ↗
“No water, I think this is just a cosmetic issue. Is it painters caulk? 10 year old house needs interior window caulk replacement? What's the best product to use that'll stand a test of time?”source ↗
“I needed foundation repairs when I saw this at my house.”source ↗
“I moved into my property and the previous owner had his dryer exhaust hole that is flush to the ground, which is so dumb as when it rained there was water going through it….I’m planning to close it and would like to know what is the best way to do so to avoid water that can seep through”source ↗
“Thanks. Trim all the way to the side or just enough to make a square? I have one of those long blade insulation knife I can probably make it flush with the rim joist from the side”source ↗
“Thinking of just trimming enough to make it square then cutting the foam to that dimension.”source ↗
“So the largest piece in can take and just spray the remaining irregular gaps?”source ↗
“How to close gaps under and above two dryer vents next to each other ? Need to prevent chipmunks and rodents from entering the crawl space”source ↗
“If you fully seal it you'll trap moisture. I would always leave some openings on the bottom edge.”source ↗
“Yeah, put some filler rod in there and caulk it up with some silicone.”source ↗
“How can we fix this brick area outside of our garage door? It looks like whatever caulking or whatever they used to hold it together has gaps now.”source ↗
“This space between their stairs and the siding on my house is full of dirt and who-knows-what, and I’m employing a broom, a snow brush for vehicles, and a battery-powered blower to try to clear the space.”source ↗
“Ultimately I’m trying to seal off any possible entry points for mice before the weather gets too cold here in western Pennsylvania.”source ↗
“There is a 5-6" diameter hole that goes all the way through the wall/outer blocks of my crawlspace. Can anyone suggest the best way to fill it in?”source ↗
“The hole is leftover from when my HVAC system was replaced in January. The company left this big ass hole that was used for some part of the old system.”source ↗
“Do I not need to use flashing tape if this is the type of install I’m doing?”source ↗
“Id ally you have through wall flashing installed...but you probably don't”source ↗
“Outside of hiring for masonry, is there anything I can realistically do or use to fill it in?”source ↗
“I'm finding it suprisingly difficult to figure out which products can be used for this.”source ↗
“Fireblocking mortar has been suggested, but it comes in 5-gallon pails for a lot of money. I just need enough for this one hole!”source ↗
“No caulk was applied on the inside wall. Is that normal? Should caulk have been applied there?”source ↗
“I'm trying to seal off any gaps that mice are using to get in. Can I use spray foam, steel wool, duct seal putty, copper wool, etc?”source ↗
“We've had some mice appear in the kitchen and believe they're getting in via the air bricks underneath.”source ↗
“I'm struggling to find a way to restrict access that doesn't involve totally blocking the air bricks.”source ↗
“Have tried to slide mesh down the back but there's something blocking it from going further down”source ↗