Best epoxy for plexiglass?

ChiefPilot · #1 10-09-2011, 05:34 PM

I think I'm about ready to give up on West systems for use with plexi, at least for the top windscreen fairing (the strip which covers the interface between the sliding portion of the canopy and the windscreen). I've made several test coupons and none have been satisfactory:

Coupon #1: Prepped with 60 grit paper, cleaned with soapy water + lint-free cloth, laid up 9oz cloth using West 105 resin + 205 hardener followed by a layer of peel ply.
Coupon #2: Same as #1, but used West 206 hardener.
Coupon #3: Same as #2, but used 1oz cloth.

All three produced a very nice finish, however, I could peel the glass off the plexi without much trouble. The slow hardener felt like it took a bit more effort, but I didn't measure it so that is a subjective observation.

While I think West will be just fine for the windscreen-to-fuselage fairing, I'm concerned about the strip across the top since that could potentially have some peel-type loads applied accidentally. There are no screws, blind rivets, etc. to use here as the whole thing is Sika'd on. I'd like to avoid sinking screws here, so any suggestions about other adhesives (or different prep instructions) would be most appreciated!

Thanks!

molson309 · #2 10-09-2011, 06:06 PM

I used West Epoxy to adhere the fiberglass fairings to the plexi on my RV-7A. I found too that fiberglass could peel off the plexi. However, I determined that once formed there is next to no peeling forces applied to the junction. 6 years and close to 700 hours later it's still adhered just like it was when I put it there.

IMHO: rough the plexi up and lay the glass over the plexi, and don't worry about it coming off the plexi. Make sure the top strip is thick enough that it won't flex under people's hands when they get into and out of the airplane. Close to 1/8" is what you need here, don't skimp. I did not do this and I am now facing having to make repairs because people have flexed it and cracked the paint.

Oh, and I did use the "clips" that Van's suggested to hold the lower edge of the plexi to the aluminum skin. These were embedded into the fiberglass layup.

Mark Olson RV-7A F1-EVO Rocket

vfrazier · #3 10-09-2011, 10:04 PM

After I made my fairings and finished them, off the plane, I reinstalled them with ProSeal and some careful masking. Made a beautiful joint and hasn't peeled at all in 10 years. If necessary, paint the backside of the plexi to hide any ugliness.

Bob Axsom · #4 10-10-2011, 12:35 AM

I used EZ-Poxy with the 24 hr hardner. It is an amber colored product. I have used it to make fairings, wing tips, as well as all of the normal fiberglass work on the RV-6A slider. It has been on there for several years and there have been no problems of any kind. Probably not much different than the West System in performance but I just did the work and moved on with no destructive testing of performance comparison.

Bob Axsom

RV6AussieNick · #5 10-10-2011, 05:46 AM

For the strongest adhesion, I wouldn't use soapy water, this may leave a very thin film that can stop full adhesion of the resin, use a good clean dry air source and blow the roughed up area to remove any loose sanding dust, never use alcohol to clean acrylic plastics, very bad results http://www.youtube.com/watch?v=cU9Ty0L0g7E

ChiefPilot · #6 10-17-2011, 08:48 PM

Lots of good ideas here - I hadn't even considered pro seal for this but since it seems to stick to everything else I'll give it a go.

Thanks!

alpinelakespilot2000 · #7 10-17-2011, 10:49 PM

Brad-
Not to dismiss many other good ideas, but I highly suspect that the vast majority of builders have probably just followed Van's directions (to use something like West Systems) and then flown without their windscreens or fairings flying off. Scuff the aluminum and/or plexi up good with sandpaper, clean it good with water or an appropriate solvent, and you should be fine. I did mine a few months ago and it seems rock solid. I haven't flown yet, though, so take this FWIW.

On a side note, I bought a 1/4 yd of carbon fiber from Spruce and sandwiched three layers of regular fiberglass between two of carbon fiber over the roll bar. It seems to have made it super stiff and I would be very surprised if I ever have problems with it being ruined by passengers grabbing it on their way in or out. Just a thought.

Good luck.

shuttle · #8 10-18-2011, 03:55 AM

A good simple tip I've read to improve fibreglass-to-aluminium adhesion is as follows:

- (After all other preparation is complete and immediately before laying up the fibreglass)

- lightly wet sandpaper the metal with resin to really tie the resin into the metal.

I've had good results with this. I've not done the windscreen fairing yet but will use the same approach with the plexiglass when the time comes.

Geico266 · #9 10-18-2011, 07:11 AM

Quote:

Originally Posted by ChiefPilot

I think I'm about ready to give up on West systems for use with plexi, at least for the top windscreen fairing (the strip which covers the interface between the sliding portion of the canopy and the windscreen). I've made several test coupons and none have been satisfactory:

Coupon #1: Prepped with 60 grit paper, cleaned with soapy water + lint-free cloth, laid up 9oz cloth using West 105 resin + 205 hardener followed by a layer of peel ply.
Coupon #2: Same as #1, but used West 206 hardener.
Coupon #3: Same as #2, but used 1oz cloth.

All three produced a very nice finish, however, I could peel the glass off the plexi without much trouble. The slow hardener felt like it took a bit more effort, but I didn't measure it so that is a subjective observation.

While I think West will be just fine for the windscreen-to-fuselage fairing, I'm concerned about the strip across the top since that could potentially have some peel-type loads applied accidentally. There are no screws, blind rivets, etc. to use here as the whole thing is Sika'd on. I'd like to avoid sinking screws here, so any suggestions about other adhesives (or different prep instructions) would be most appreciated!

Thanks!

Try not using soap and use a cleaner or solvent. Soap could be the problem causing the resin not to stick to the Plexiglas. I am no expert, but soap is like a mold release. JMHO

ChiefPilot · #10 10-19-2011, 07:57 PM

I think it was the washing after sanding the plexi that was screwing me up. I made up a test coupon which was cleaned only using compressed air and a tack cloth. West 105 + 206 stuck the glass very solidly to the plexi to the point where the lip I left hanging off the edge tore off before I could peel any of the glass away.

Thanks! You guys are awesome!
Brad