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Advice sought Re poor FG bond on plexi

jimbo

Well Known Member
Patron
I made the FG layups for the windscreen fairing over the roll bar for the RV9 sliding canopy lip. Everything seemed to go well until a close inspection a day later when I opened the canopy. There is a 13 inch strip centered near the top at the rear edge where the epoxy partially delaminated from the plexi. My fairing width is 1-3/4 inches. The lip overhang is about 1/2 inch, then about 5/8 inch of delamination, then 5/8 inch of good bond. I used 4 strips of FG cloth varying from full width at the base to 7/8 inch on top.

Not sure what to do about the area of delamination, if anything. Edge in this area will lift up slightly but not enough to get sandpaper in there. I am concerned that if I try and pry up the edge to get sandpaper in there, vacuum out loose dust from the edge, and maybe some squirts of some kind of adhesive or more West system epoxy that I may break more bond, plus, it might not even work.

I did scuff up the plexi good with 60 or 80 grit-whatever it said in the manual, vacuumed off, then wiped down with mineral spirits. My possible fault was that I did not use the double wipe method.

Any ideas out there for the experts in VAF land?

Jim
 
You may want to double check that the bond in the other areas is strong. If there was some contamination that prevented a proper bond in that 13 inch area, it is likely it is in some other areas as well. Better to find out now then in a couple years after its flying and all painted up nicely.

I'd hate to say it, but it may require peeling it all up and starting over.
 
You may want to double check that the bond in the other areas is strong. If there was some contamination that prevented a proper bond in that 13 inch area, it is likely it is in some other areas as well. Better to find out now then in a couple years after its flying and all painted up nicely.

I'd hate to say it, but it may require peeling it all up and starting over.

I looked it all over. Except for a few inches of transitional area, everything else appears well bonded to the plexi. As I see it my options are 1) put another strip of FG cloth and epoxy over the top to stiffen it up; 2) try to put some stick to anything adhesive along the underside edge of the plexi and FG lip-not sure what adhesive might work though; 3) rip off that 13 inch area and open a can or worms. Pretty sure I would have to cut the ends and along the front of that strip leaving some ragged edges. Prep again and fill in the cutout area with new layups.

Update:
Thanks for all who responded. I ended up cutting out a 27" section, recleaned, scruffed up with 50 grit, cleaned again, then laid up new FG layups. Applied a final layup over the old section as well as the new. Opened the canopy 2 days later and everything looks good. The overhang lip is stiffer with the additional FG cloth layup.

I'm glad I decided to cut the poor bond section out. Although I could have epoxied the strip back in place after prepping the surfaces I was uncertain how the strip would lay back down-even using fasteners. The new layup section bonded well with the original and under the lip you can hardly tell there is any joint. It was easy to cut the poor bond section out. All I did was get a knife under there and start prying. Once I felt a lot of resistance at the ends of the poor bond section, I stopped. Then I took a small round file and started filing to cut the ends of the strip watching that you do not abrade into the plexi. Easy peasy.

Why did I have a section that did not bond well. My guess is that I used some gorilla duck tape in that area at one time to position the plexi for fitting. I think the adhesive go onto the plexi and sanding didn't remove it all. (Now I know to clean before sanding) Then the mineral spirits I used for the final wipe also probably didn't remove it (also now I know to use the 2 wipe method and I hear alcohol is a better solvent). I hope others can learn from this.

Jim
 
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Jim - you may be able to inject some epoxy into the crack. I would pm DanH. I consider him to be one of the "guru's of glass". A picture would be good.
I am not much help as I fabricated my fairings out of metal.
 
Lift the layup up and really clean things well meaning both sides the plexi and glass layup. You may have gotten both dirty. Then mix up ksome fresh resin and rebound it down, drill some holes in the layup right thru the plexi and use soft AL pull rivets to hold it down. Then fill the rivet holes at the heads of the rivets. If you counter sink the rivets you won't have to put another layer of glass to hide them. The rivet heads should just be below the upper surface of the glass layup.
 
delaminating w/s fairing

I was flying my newly purchased RV-6 home & nearly scared the **** out of myself when a loud bang & very loud screaming sound absolutely drowned out my Zulu headset. The plane ran fine & had no control abnormalities so I elected to returned back to the last airport & discovered the W/S fairing totally delaminated along the back edge, it was still holding around the bottom forward edges. I secured it with a number of strips of '100 mph tape' & got her home that way. I fixed this fairing by removing all the W/S screws I could get to, align drilling & countersinking the W/S fairing, applying a bead of ProSeal under the fairing & screwing it down. Not the prettiest solution, but does the job. Moral- you don't want to chance a poor bonded W/S fairing.

On my other plane, RV-7A (since sold), I once experienced a persistant whistle and had a real hard time diagnosing where it was coming from. Turns out there was a small (1/4" maybe) void between the W/S fairing & plexi, and the wind was literally whistling thru it. This was fixed by injecting some epoxy into the small crack. Moral here- you want a good seal all around.

On my latest projects I have been removing every other W/S screw before laying the fiberglass, put 2 layers in place, then re-install the missing screws. I then continue with more layers to desired thickness. This insures a more secure attachment between the plexi & fiberglass. I also be sure that the embedded screws are in the areas most likely to be grabbed by unwary passengers, thus further helping to avoiding unwanted induced delaminations.

Back the the RV-6- reason for it's poor bond was the plexi surface appeared to only have been roughed up with Scotchbrite pads.
 
Proseal

My delamination from the plexi ocurred on top of the windscreen. I have about a two inch strip of which about one inch overhangs the rollover bar to the rear. I had a bad habit of placing my hand on that strip, using it to leverage myself out of the airplane. The fiberglass strip (carbon fiber, actually) would "rock" back and lift the forward part of the strip off the plexi. I applied a two inch piece of masking tape over the plexiglass to protect it. I was able to raise the fiberglass strip enough to squeegee some proseal underneath the glass. I let it cure a couple of days and haven't had any issues for +400 hours.
 
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