In the original experiment, I made a channel in the Pink Foam Board and put a bead of spray foam on the bottom of the channel, then placed the EMT on top of it. The foam filled the channel and covered the EMT. That was the good part. The bad part was that the foam overflowed above the channel's sides. in order to get the spray foam flush with the Pink foam that I made the channel from, I had to trim off the excess hardened spray foam.
(One of the great features of the spray foam is that it makes its own skin.) When I cut off the excess, I took off the skin with it. So when I put Glidden Gripper on the cut foam, the foam got soggy and didn't hold the EMT as well. Since I have to put primer on the spray foam to put canvas on top of it, I needed a new technique so I wouldn't have to remove the skin of the spray foam. In other words, I want the spray foam to dry flush with the Pink Foam so I can cover it with canvas.
I tried to use the locktite for a third time for this idea. I barely got the foam out of the can but I did put a bead of foam in the channel and then put the EMT in the channel. I then put wax paper on top of that, then a flat piece of scrap and a little weight. The expanding spray foam lifted the flat piece and overflowed the channel. So that was a failure because I didn't use enough weight. Now the LockTite can won't work anymore.
This time I'm trying the Blue Great Stuff, this can is still working well. Instead of a continuous bead of spray, I'm spot welding. I put a dab of spray foam in 3 places in the channel then put in the EMT and covered it with wax paper, a flat piece, and a heavier weight.
There was a crease in the wax paper and I pulled it off too soon. so a little bit of spray foam stuck to the wax paper leaving a hole.
The next attempt I used the Great Stuff over the EMT that I used Gorilla Glue on. I made very small beads of foam over the EMT in the channel and then covered it with a new piece of wax paper. Then covered it with a flat piece of scrap and a heavy weight. I left it overnight. The results were perfect.
IMO: This is suitable for putting primer and then canvas over.
Just a thought here. If I were to do this to frame out a large piece of Pink foam board with EMT, I would do this in small sections. This way the foam would have somewhere to go when it expands.
