I'm a little bit (cough) OCD so as I built my house if I saw a crack somewhere I filled it with Great Stuff.
I think I used about 300 cans of it and I needed a way to trim it flush since I was using it around all my outlets and doors and windows plus a few places that are probably uncommon to use it like around the 1/2 inch gap I left between my Oak tongue and groove floors and the wall to allow to expansion contraction.
This turned out to be a big time saver later when I was sanding and putting polyurethane on the floors since there were no cracks to collect that fine saw dust that allows seems to get blown around as soon as you begin the finishing process.
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: OCD's Throw Little Away...
Somehow I had a large meat knife I guess it was with a broken handle. I probably meant to make a new handle for it but I happened to find it just when I was doing a lot of spray foaming and I got to looking at the blade and decided to make a tool from it so I could trim expanding foam flush to a surface and hopefully in a fairly fast manner.
I ended up sawing the handle part of the steel blade of probably with a grinding wheel on edge but I don't actually remember since I bumped my head a while back and seem to have misplaced a few or more thoughts but if I had to do it now I would use a grinder so in all likelihood that is more than likely what I did.
Sorry to Digress...
I found a scrap of angle iron about an 1/8 of an inch thick and about 1" by 1" and sawed a piece off about three inches long.
I lay the blade flat on the workshop floor set the piece of angle iron on top where the shank would normally be and welded it solidly to the blade. I started by just tacking the corners because I wanted it to stay flush and welds can put a twist to your project you really don't want so I tacked the corners and then ran a bead all around and cooled it with a wet rag as I went.
Since I wanted this to be both a lefty and a rightly tool I got my grinder and ground an edge to what would normal be the back side of the knife turning it basically into a dagger. I use my spool sander to get a pretty good edge on it and I ground off the distortion on the opposite side where the weld was made and used the spool sander on that as well to make the face touching the wall very smooth.
I had some odd sized piece of oak laying around and found a piece about an inch wide 2 inches high and about 7 inches long. I use my table saw and ripped a slot in the center of the one inch side about 3 inches long. It took a little fine tuning but I got a good fit on the piece of angle iron with the wood handle, then when I was sure it fit I clamped it and drilled a 1/4 inch hole through the handle and through the angle iron and drove a piece of dowel rod with glue through it.
I drilled a second hole also through the angle iron then unclamped it and added a few more just because and then I used my belt sander to shape the wood handle so it felt comfortable to hold.
I tend to not worry excessively about accidents since I keep having them but looking back it probably would have made more sense to fit the handle, then use the belt sander, then put in the dowels since basically I had to hold onto a sharpened knife handle as my table heavy duty tried to snatch it from my hand so use your best judgment and don't get hurt.
Step 2: Not for Use by Children Under Five
It's pretty obvious how you use it one tip is to be sure it's completely dry since running into gooey spot gums the blade up and makes it stick and what you want is to make long smooth cuts either by slicing or using a sawing method. The smoother the blade face and the sharper the edges the cleaner your cuts will be,
When I put my Oak floors down I left a gap around the perimeter since the main room has a 47 foot span and that makes for a lot of expansion and contraction as the season flash by. I wanted this sealed tight mostly because Florida has a lot of bugs and I figured it would be flexible if the floor felt the urge to stretch when the humidity climbed.
Since the foam expands just as seen on TV it will stick to the bottom half inch of wall board and be about that high above the floor. Trial and error taught me to first make a cut the entire length of the wall starting with the blade flush to the floor. I then used a 12 inch sheetrock trowel and slipped that into the cut then put the blade flush to the wall and used the steel trowel to stop me from cutting any deeper than the floor itself. You just walk the trowel down the wall and you'll end up with a pretty sharp inside corner and since the blade didn't penetrate below floor level no gaps we're made that the really small bugs might find a way into.
When I was doing around my doors and windows I found it pretty easy to end up with long strips of expanding foam that I could quickly gather up and tuck in a large box. When the box got full I took them up to the attic and dumped them where I would eventually spray blown in insulation so this may sound trivial but I used close to 300 cans of Great Stuff ended up with probably a roll or two of insulation that would otherwise end up in the trash.
Other places I used Great Stuff was here and there I foamed sections of the plumbing drain lines especially around drops or 90's and it went quite a long way in making my plumbing silent as far as not hearing water running inside a wall if someone uses the shower on the top floor.
I like Quiet.