How To Use Expanding Foam at Your Cabin

Thinking about using expanding foam for pest control at your cabin? Learn all about spray foam and whether it's the right stuff for the job.

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Expanding foam, also called spray foam, is a type of thermal insulation. It goes on as a thin liquid foam, then expands to 30 to 60 times its original volume before fully hardening. Most often used in walls, it’s also good for insulating floors and roofs and eliminate air leakage. It even works for pest control!

Spray foam insulation products fall into two categories: closed-cell and open-cell. The difference is in the small bubbles or “cells” that make up the foam. Open-cell foam bubbles are not airtight, making the foam softer, more flexible and less effective at insulating. Closed-cell foam is full of unbroken and airtight bubbles, making it more dense, rigid and better at insulating.

Both foams resist heat flow, and this resistance is known as R-value. Closed-cell foam has a higher R-value (R-6), making it the more effective insulation overall. It’s also waterproof, unlike open-cell foam products.

Open-celled foam averages only R-3.5, but expands much more, making it ideal for hard-to-reach areas and soundproofing. It’s slightly more affordable but won’t insulate as well as closed-cell foam. Understanding these basics is key when deciding if you should use expanding spray foam at your cabin.

Can You Use Expanding Foam on a Wood Cabin?

If you’re considering insulating your wood cabin, spray foam is an excellent option. Here’s why:

When considering other forms of insulation (like fiberglass batts and blown-in insulation), you need a vapor barrier to prevent moisture from forming in the walls when warm indoor air and cold outdoor air meet. Closed-cell expanding foam acts as insulation and vapor barrier all in one.

I used closed-cell foam to insulate my cabin in the woods and never regretted it. It keeps us warm and dry every winter, not to mention cool in summer. When building a wood cabin, spray foam, particularly the closed-cell stuff, nicely fills the wall cavities between studs.

How To Use Expanding Foam

Here are the basics for successful expanding foam installation:

Decide how much foam you need

Single-use cans of spray foam are available at hardware and big box stores and online. These cans are great for insulating small areas and filling gaps around windows and doors, but you’ll need much more for full-blown insulation jobs.

That’s where large, two-part DIY spray foam kits come in. These aren’t cheap. But if you have more than a few small spots to spray, you’ll be much better off with kits rather than small cans. (Note: Due to supply chain issues, these kits are difficult to find at present.)

If you have a massive amount of foam to apply and would rather avoid doing the dirty work yourself, consider hiring a dedicated spray foam application company. They’ll arrive with a tanker truck full of foam and apply it wherever you direct them.

Check the expiration date

Spray foam works best when it’s fresh. Using expired or nearly expired foam can result in poor application and shrinkage after hardening, decreasing its R-value and vapor-stopping abilities.

Invest in an applicator gun

If you’re planning to spray more than a few areas of your cabin but don’t need a large foam kit, purchase an applicator gun to dispense the canned foam. The single-use cans found in most hardware stores come with a thin plastic nozzle, but they’re also threaded on top to accept a thread-on gun-style dispenser. Adding a gun to a spray can allows more accuracy and less waste.

Check the temperature

It’s important to apply expanding foam at the proper temperature. When the foam or surface being sprayed is too cold, the foam appears to set, but will not stick to the surface properly. In time, the foam will shrink and pull away from the edges of the cavity you’re filling.

Spraying in temperatures of at least 40 F is ideal. If you’re working on a day with little humidity or applying foam on an exceptionally dry surface, lightly misting the area with water before you spray will help the foam expand and cure faster.

Protect yourself and your work area

Expanding foam can be tricky to remove from your hands, arms, clothing or surrounding areas, so be sure to wear protective gear, or at least old clothes and gloves. Wear a mask with goggles and a mouthpiece to protect your eyes, and avoid breathing in the fine mist of chemicals from your spray foam.

Most large spray foam kits come with masks, gloves and a full bodysuit. Be sure to place your spray foam dispenser on a piece of cardboard when you’re not using it to prevent excess foam spilling on the floor.

Don’t wipe up your mistakes

If you happen to spill foam on the floor or spray it in an unintended area, just let it set and harden. Resist the temptation to wipe it up while it’s still wet, because this will spread the foam and make the mess worse. Let it harden and scrape it off with a putty knife.

Don’t rush

Go slowly and apply the foam in small, layered increments. Wait for each layer to expand before applying the next one. This will help reduce lumpy layers and avoid waste.

Once your foam has set, use a utility knife to carve off any bits protruding beyond the space you’re insulating. When you’re done for the day, spray solvent through your dispenser to clear it out. Otherwise, the foam inside will harden, and your dispenser will be useless in an hour or less.

Why Use Expanding Foam on Your Cabin?

Thanks to its aggressive expansion, spray foam usually finds a way into nearly every nook and cranny if it’s properly applied. That prevents air leaks and heat loss, and many homeowners report much lower energy bills each month.

Because closed-cell foam prevents moisture from forming in wall, roof and floor cavities, it protects from mold in these areas. Condensation cannot form because the spray foam stops the inside and outside air from meeting. That’s why houses insulated with spray foam are some of the most airtight and energy-efficient.

Wondering about expanding spray foam for pest control? Filling gaps, cracks and holes with the closed-cell stuff is a great way to stop rodents and other troublesome critters dead in their tracks. It’s far easier to prevent rodents from entering a cabin than removing them afterward. Open-cell foam might help deter pests, too, but its lower density means it’s much easier for them to chew through. Here are a few tips for pest-proofing the cabin.

Be sure to use spray foam around all incoming and outgoing water pipes. Electrical conduits are another prime entry point for unwanted critters, so use foam around these, too. Finally, be sure to fill any gaps where your walls meet the underside of the roof with foam. It’s easy for cracks to escape your notice here, so be extra diligent.

Robert Maxwell
Robert Maxwell is a writer, videographer, photographer and online strength coach based in Northern Ontario, Canada. He grew up on a rural self-sufficient homestead property where he learned the skills to build his own home from the ground up, do all his own vehicle repairs, and work with wood, stone and metal to find practical DIY solutions to many everyday problems.