Over the years I've noticed a few references here about epoxy not adhering well to acrylic, when doing fiberglass layups for windscreen fairings. Recently I've seen a couple of RVs where the fairing was delaminating over the top of the roll bar, and/or chipping away entirely.
On a whim I decided to try a little experiment. I bonded both canopy and windscreen to my airplane with Sikaflex 295UV, and I had some primer- Sika 209D- left over from those jobs. Technically, the primer is an adhesion promoter for the urethane. I wondered if it would improve an epoxy bond as well.
I scrounged two trimmings from a canopy, and attacked them with 60 grit sandpaper until I had a nice uniformly rough surface on each. One of them got a quick wipe with denatured alcohol, the other got wiped first with Sika 226 cleaner (now known as Sika Aktivator 205, which they specify as the first step in the bonding process), and then coated with the 209D primer. After waiting the requisite time for the primer to dry, I mixed some West 105 with 206 fast hardener. Then laid up a single layer of cloth on each piece of prepared acrylic. After that I went over to the cool antique fly-in happening around the corner from me, and hung out for several hours looking at cool old airplanes
About 8 hours later, I tried a very unscientific pull test on each part. The glass on the bare acrylic peeled off cleanly, leaving no apparent residue. The primed part didn't want to let go so easily. Pulling hard, I was able to tear a corner loose, but strands of fiberglass remained embedded in resin, still attached to the acrylic.
Obviously, an unscientific test. Among other things, I didn't wait long enough (several days, at least) to allow a proper post-cure of the epoxy. And there are concerns about applying nasty solvents to one's ?ber-expensive bubble. Duly noted. I have yet to apply the knowledge I gained, though I'm considering it since I'm about to lay up the windscreen fairing. I thought it worth sharing in case someone is interested, or wants to try it themselves.
Your mileage may vary; tax, license and dealer prep not included, etc, etc.
On a whim I decided to try a little experiment. I bonded both canopy and windscreen to my airplane with Sikaflex 295UV, and I had some primer- Sika 209D- left over from those jobs. Technically, the primer is an adhesion promoter for the urethane. I wondered if it would improve an epoxy bond as well.
I scrounged two trimmings from a canopy, and attacked them with 60 grit sandpaper until I had a nice uniformly rough surface on each. One of them got a quick wipe with denatured alcohol, the other got wiped first with Sika 226 cleaner (now known as Sika Aktivator 205, which they specify as the first step in the bonding process), and then coated with the 209D primer. After waiting the requisite time for the primer to dry, I mixed some West 105 with 206 fast hardener. Then laid up a single layer of cloth on each piece of prepared acrylic. After that I went over to the cool antique fly-in happening around the corner from me, and hung out for several hours looking at cool old airplanes
About 8 hours later, I tried a very unscientific pull test on each part. The glass on the bare acrylic peeled off cleanly, leaving no apparent residue. The primed part didn't want to let go so easily. Pulling hard, I was able to tear a corner loose, but strands of fiberglass remained embedded in resin, still attached to the acrylic.
Obviously, an unscientific test. Among other things, I didn't wait long enough (several days, at least) to allow a proper post-cure of the epoxy. And there are concerns about applying nasty solvents to one's ?ber-expensive bubble. Duly noted. I have yet to apply the knowledge I gained, though I'm considering it since I'm about to lay up the windscreen fairing. I thought it worth sharing in case someone is interested, or wants to try it themselves.
Your mileage may vary; tax, license and dealer prep not included, etc, etc.