by MatBirch » Sun Mar 24, 2019 7:18 pm
So, I didn’t bother with a bunch of pics, since you’ve all seen plenty. I did a couple of experiments on some adhesion, materials, and fairing compound.
For the canvas on foam, I tried one with the old standard of thinned TB2, and one with gripper primer. I did the same for both- paint the surface, paint the back side of the canvas, then place it and smooth it in with a gloved hand. (Foam was sanded to break the shine and cleaned.) after a couple of hours, I top coated 1/2 of each sample.
I wasn’t planning to test at the end of the day, but when I was fiddling with it, the TB2 piece fell off in my hand! Like dollar store masking tape on waxed glass... I don’t know what I did wrong. That led me to go ahead and test the gripper piece. It was really impressive! I only pulled a little bit to opt for full cure. After 24 hours, I pulled a bit more and it was about 1/2 again better yet! Very impressed. I went back and put another TB2 sample together, and this time went with full strength TB2. My thought is that maybe I was too thin on the last one??? I’ll give it a day or two, but I’m sold on the gripper and am planning using it.
For fairing compound, I mixed up a batch of Red Devil ultralight spackle with a bit of gripper. I didn’t have a good way to measure, so I just sort of winged it. I made it so it was thick enough not to flow out, and dribbles would hold a form. It spreads with a spreader, but you’re not gonna brush it. I think I could have gone even thicker with a little less gripper. My goal was easy sanding but with better stick and flexibility than the spackle alone. I had an old test I’d done with gripper on plywood where I’d put a second layer of canvas on 1/2, creating a seam. I spread a nice thick layer, smoothing out the seam trying to hide it. I also put some damage in a hunk of foam to try it as a repair filler. I left it overnight to dry. It did shrink a bit, and seemed like maybe it wasn’t cured throughout. It seemed pretty soft. I went ahead and tried sanding it, expecting it to just gum up and get messsy. Turns out it was indeed dry throughout, and just flexible. It sanded quite well and didn’t gum up at all. Exactly what I was hoping for. I went to the foam piece and expected to break chunks off like you would with a pile of dried spackle. It would not. It will not come off the foam at all. Little bits of foam just come away with it. Again, very impressive! Lastly, I peeled the second layer of canvas off of the plywood sample. It peeled off down to the overlap, and finally came off. The compound stayed stuck strong to the canvas, even doubled back while peeling! There are micro cracks in it now, but it’s all still one homogenous piece of canvas/gripper/gripper&spackle.
Next I plan on trying it as a gap filling adhesive for corner joints and butt joints on foam. If the sample on the bare foam is any indication, it will provide a super strong (relative term) joint with a level of flexibility allowing for some forgiveness during construction.