
Cutting Spray Foam Insulation
This might be our shortest post ever. It’s a simple little tip to make you go DUH! It’s how to cut spray foam insulation.
BACK STORY: Recently while helping Emily at merrypad.com redo her bathroom for DIY network we spray-foamed her bathroom window gaps because when we removed the old trim her bathroom was suddenly like Ooook-lahoma, where the wind comes sweepin’ down the plain.
Anyone who uses this great stuff (see what I did there? If not, you’ve probably never used spray foam insulation) knows that you spray away, you don’t think you used that much, then you come back the next day and the area you sprayed looks something like this.
PRO TIP: Before you break the seal on that can of spray foam, walk around your house and find all the places you can spray this stuff. Once you break the seal you better use it all, because it’s basically a one-time use thing. There’s no saving it for later. It hardens up and you just wasted a whole can. I once heard Adam Carolla compare a can of Great Stuff Foam to a beer. Once you open that sucker you chug it. You don’t put the cap back on it and save it for later.
I’ve tried lots of ways to cut away excess foam. The most succesful up to now was my Husky utility knife with a brand new blade. And that works ok for small amounts of foam, but once you get past the depth of the blade you start having to hack at the foam and dig at it and the next thing you know you’ve got shredded up foam.
Well here’s the tip.
First have a big breakfast meeting and have it catered by a bagel shop or someplace that will throw in a big old cheap, serrated bread knife.
Next, use that sucker to saw the foam. Hold it as flat to the wall as possible and it’ll saw through the cured foam like nothing.
And, that’s it. And yes, I could’ve probably written this post in one sentence. Or even just a tweet.
Is there a better way of cutting this foam that I’m missing?






























I’ve used a drywall saw, but the blade you have is much more flexible. Definitely the way to go. The serrated blade is key.
I’ve never tried the drywall saw but I imagine that gets nasty.
Serrated blades are great for cutting thick foam. If you are cutting 3 inches thick or less try an Olfa L-2 utility knife. (Get the heavy duty blades for more dense material) These work great on spray foam, board type insulation, soft foam (for tool/pelican cases) etc. Good clean accurate cuts. I have one at home, one in my truck and two at work (narrow and heavy duty setup) so I’m never without.
Way to be prepared, Kirk. I usually just carry the Milwaukee Fastback™ Utility Knife with me at all times but I like the lightweight L-2 as well.
The foam should have been sprayed correctly at the time of instaling of new window.I had used foamcoinc spray for my bedroom window and it adjusted itself ,i don’t know how it happened but the foamcoinc guys say that their secret composition does this ,but yes i didn’t have it all over after spraying.Just try that product
Thanks, Mike. It wasn’t a new install and I was just using the end of a can and getting as much in as I could, but yes, I’m sure it could have been neater, but something tells me you work for FoamCoInc and go around different sites and spread your name around.
Nope, I was just suggesting you.