Cutting Batts with a Knife
This kitchen knife is the perfect tool for making lengthwise cuts in fiberglass insulation.
If you’re insulating a house and have to cut a bunch of fiberglass insulation, you could try compressing it and cutting it with a utility knife, but there’s a better way. Roger Apted of Milton, Wisconsin, was rehabbing a 19th-century house and getting ready to insulate the walls, but he had a lot of odd-shaped stud bays, which meant a lot of lengthwise cuts in the fiberglass insulation. He looked around for the perfect tool to cut it with, and came up with a chef’s knife. This is the perfect tool because it has a long blade that’s broad at the base and it tapers to a point. Now, because there’s a coating on the back of the kraft paper facing that will gum up the knife, before making the cut Roger coats the blade with silicone spray.
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I am an advanced DIY and I am also a chef. While this may look like a "good tip" it makes no mention of how that nice chef's knife will be probably ruined by using it for this purpose. One or two cuts will only dull the blade, a repairable condition. But as it is mentioned the tip is for someone who has to do a lot of cuts the chefs knife will be trash when done. I have chef's knives worth more than $150. I'll stick with the utility knife thank you.
we did that back into at least the mid 70's, used a 7" insulators knife. Nothing new on this idea.
I also am a DIY. Having just done a job which required extensive cuts on both 5 1/2" Roxul and unfaced 8" fiberglass I found that an 18" hand saw was an excellent tool. It was easy to make straight square free hand cuts on both materials, and it didn't dull quickly like my utility knife did.
I've had great luck using an electric carving knife. No force is required, you can do it standing up and it'll cut right angles to accommodate electrical outlets.
I passed the tip on to my girlfriend because her son is a contractor. She called back to say but of course. Turns out she's done it in the past because she couldn't find her utility knife. Said it does work great.
Roger must be single. If my wife ever caught me cutting insulation with her good knife there would some stuff hitting the fan.
This is the kind of idea that gets our kind (men) in trouble. If you are a newlywed, please don't do it. Trust me I have been married for 13 years. Just don't.
Guys....puhleeze. There's more than one chef's knife in the world and some are inexpensive enough to use on a job like this. The suggestion isn't that you use one of your Wusthofs.
I buy old kitchen knives at the local thrift store. They usually cost $.50 to $2 depending on condition. You can get long ones, short ones, etc. While you're there, pickup a sharpening steel for another $.50 to keep a good edge on them.
Another thing you can do with these knives is draw the outline of a special purpose blade on them with a Sharpie pen, cut it out with a Dremel tool, sharpen it up and you've got the perfect tool for a specific job.
You can use this technique to make small knives that are much heavier-duty than utility knives or the paring or steak knives you can also buy at the thrift store. Best of all, you can make small scrapers with narrow edges or angled edges to fit specific tasks.
The knife is good,. but I fund a much better way. I use (an old) electric meat carving knife. The two serrated blades slice back and forth so the knife cuts thru the batts like butter. I can make any shape or size I need. This device saved a lot of time and frustration insulating an 1920's remodel.
The knife is good,. but I found a much better way. I use (an old) electric meat carving knife. The two serrated blades slide back and forth so the knife cuts thru the batts like butter. I can make any shape or size I need. This device saved a lot of time and frustration insulating an 1920's remodel.
Where are they still building residential construction with 2x4 studs on exterior walls as pictured in this video? That would be an R 11 insulated wall. Or is this an old movie set recycled from the 70s?
Been doing something like that for the last 25 years except using an old bread knife. It saws through it easily. Works especially well with roxul mineral wool. One of the benefits of sawing with a bread knife is it does not need to be sharp
Flipping those batts over with the kraft face down makes cutting even easier whether using a kitchen knife or utility knife. Compressing the fiberglass with a heavy straight edge also helps. I also use a cutting board made of plywood marked off in inch increments to eliminate stretching a measuring tape across the unwieldy blanket of fiberglass.
That tip, is about as old as the hills! When I first became a Pipefitter's helper we were the ones that had to insulate the pipe, the helper's job & not the fitter's. I moved into the pipeshop from the millwright's shop in 1970. And, started insulating soon after that.
As an ol'fart who's been doing DIY insulation projects for over 40 years, Long ago a found the perfect knife for this and still use it today: a Machete! It's long blade makes for easy long straight cuts and cross cuts in one easy swipe. The rounded end rides easily over any cutting surface or subfloor plywood without snags, or tearing the grain of the board.
They're still sold and often come with a scabbard so you can hang it on your belt. Good for ladder work where you may need to trim some on the fly between overhead Joists or Rafters
I use hedge shears.
Re: Nice chef's knife; nobody would do that. Pick up a cheapo or use an old one.
Re: 2x4 walls; still common in the south and of course remodels. And R-13 is standard while R-15 is also easily available.