When I was in school, we used to hook layers of foam insulation board (both blue and pink) with what we called “Green Glue.” I’m pretty sure actual green glue is something different but this was a product by DAP that was a foam safe contact cement that came in a green can. The problems with it were that it always made a gummy, hard to carve film between layers, it was very stinky, and it was complicated to use. It also didn’t’ always hold up very well.
We also used Liquid Nails from time to time, but for big applications it never fully set in the middle and once it did set it wasn’t carvable.
Then, a few years ago, a friend told me how they’d been working a summerstock where they used Great Stuff as a foam adhesive and how they’d never use anything else again. I tried it, and I agree. Great Stuff is the right stuff for this job. It isn’t without it’s quirks, but it’s better than the old school methods. You can also use this to hook foam to wood.
It does have some fumes so take precautions and DO NOT GET THIS ON YOUR SKIN. For most people if you do get a little on it just doesn’t come off for a week or so and it feels icky. I did see a person have an allergic reaction once, and it wasn’t pretty, so that’s a possibility, but more than that, it’s not healthy for you. I wear gloves, sleeves and eye protection and suggest you do too. I also always use it in a well ventilated area or outside.
Step 1- Prepare
Cut to size or otherwise prep the two surfaces you are gluing together. Set them on a drop cloth that has plenty of extra space. Sometimes this spray is trigger happy and once it’s on something, it’s on.
Then read the can and open as it directs. Be aware that once you use it, you either use the whole thing or you risk wasting the rest. Sometimes you can cut the straw off later and get some more out or swap the straw with a new can, but most of the time it’s best to just plan to use it in one sitting. Also make sure your safety equipment, like gloves and goggles are ready to go.
Make sure you have weight available, because you’re going to want to keep the top weighted down while it cures. I’ve found the best way is to take a piece of plywood about the same size as what I’m gluing together, lay it on top and then add stage weights fairly evenly to the top of the plywood.
Step 2- Spray and Weight and Wait
Spray the great stuff all over the top of whatever surface is going to sit on the bottom while it cures. Lay the next layer on top and weigh it down. (I don’t recommend doing more than one layer at a time… or at least wait an hour or so depending on the weather between layers. It won’t be all the way cured after an hour, but it’ll be close enough.)
Step 3- Keep an eye on layers
At this point I usually move on to a different chore, whether it’s gluing other layers together or a different project entirely, but while I’m waiting I keep an eye on this and if the layers start shifting, I take a minute to nudge them into alignment. The Great Stuff that expands bigger is more likely to cause shifting, but I have used it when it’s been the only stuff left and I just watch it even more carefully and use extra weight.
Sometimes, if I’m carving all the edges, keeping the layers aligned isn’t so important so I don’t watch as carefully. If I want to keep a straight edge though, I really watch carefully. It is possible to keep it aligned perfectly.
Step 4- Repeat with other layers
Repeat those steps with the other layers until done. If I’m gluing a lot of layers together, I usually glue every other layer together first, and then go back and glue pairs of layers together.
Step 5- Done
Once it’s cured you are done gluing and ready to do whatever carving you’ve planned. Have fun!
They’ve recently released a Great Stuff Pro line with a specialized can that hooks up to a more sturdy, cleanable, reusable gun. I haven’t had a chance to use it yet, but when I do, I’ll let you know what I think. My prediction is that the cleaner will end up costing a bit every time it needs to be used, and that these guns will be VERY cost effective for large scale use, but not so cost effective for a small project or two. I also predict the cleaning process will be annoying.
Someday there will be pictures with this article. I’ve apparently never taken pics of this process, but I will next time I do it. I’m starting to post some specific tutorials on projects that used this technique and wanted to have this article separate instead of describing the process for each article.
Other uses for Great Stuff
I also use Great Stuff as a detailing tool in certain applications. Most recently, I designed a gingerbread house for The Brothers’ Grimm Spectaculathon and I used Great Stuff as the frosting details. In my past it has created tree trunk texture, rock texture, under the sea coral texture and more. I’ve also used it as an accent on curved moldings, but for that kind of application you need to feel confident in your ability to spray evenly and with control. That takes some practice, but once you have it, the uses for Great Stuff tend to present themselves.