You need to prime your timber first.i assume what is happening is that between the timber and the glass, too much of the epoxy is being absorbed.
You really need to coat your timber with epoxy first, bonus points if you thicken those coats with cabosil or silica, let that tack and THEN add fully wetted out fibreglass.
Both samples are indeed porous from absorption into the wood. I’ll remake both samples with the tacky layer method and repeat all the tests tomorrow
And lo, it is done. The new samples were made by priming the bonding surfaces of the wood until tacky (2 hours for epoxy, 5 minutes for wood glue), and then transferring in a sheet of fiberglass that has been oversaturated with adhesive. I left these to cure for 3 days, because the wood glue sample was doing a Pringles chip impression on day one, presumably because there was more moisture that had to escape.
This time there was a difference in the bending test. The two samples still had a similar breaking strength, but the wood glue sample had a larger bend radius and failed more gradually, while the epoxy sample created a sharper failure point and failed in a more brittle manner.
(Wood glue)
(Epoxy)
In the dry chisel test, there was less of a discernible difference between the two adhesives, since the bonds appeared to be stronger than the wood. In both cases my chisel preferred to go through the wood than through the fiberglass, but similarly to last time, the epoxy sample had a tendency to skate the chisel while the wood glue sample had less cut resistance.
(Wood glue)
(Epoxy)
As you can see by the samples sliding around under heavy clamping force, I could no longer start the cut with the flat of the chisel like last time. I was able to get in with the corner of the chisel, and I would rate the epoxy sample as being more difficult to start the chisel cut.
I was able to get in with my fingernails and peel up both of the fiberglass samples, but the wood glue sample was much more resistant. The fibers tended to rip in half and fray away from each other, while the epoxy sample peeled up more easily and in a single piece. After soaking for 2 hours in water, the epoxy sample did not change but the wood glue sample became as easy to peel up as the fiberglass.
In the wet chisel test, the wood was of course much weaker in both samples. Since the epoxy layer still had a tendency to make the chisel skate, I was able to get a piece to delaminate with it. Since the wood glue still did not have any cut resistance, my chisel went through it instead and kept cutting into wood on the other side.
I love this science dude! Nice work!
Glad to hear it. And thanks to everyone for asking more questions and keeping me honest, it has greatly increased the scienceness
i’ve really enjoyed this thread. I never would’ve thought of using glass fabric with wood glue. on the surface it seems like madness, but clearly some very interesting results are happening here.
Now I want to see one with construction adhesive or polyurethane.
Update: I attempted to laminate a deck with this method in a vacuum press, and attempt number one failed pretty miserably. I had a six inch wide strip of fiberglass underneath each of the face plies, with the same amount of wood glue that I used for the previous tests. I think that the outside edges of the layup stuck to each other first, and the center region continued expanding from the moisture, leading to massive ripples on both sides.
The second attempt was successful, using full width fiberglass, a little bit less glue, and a sheet of 3 mm birch plywood placed on top of the layup to restrain ripples during vacuuming.
It took about a week to feel like the wood was relatively dry, but the board looks to be fully consolidated, and it took the shape of my mold perfectly!
