Gelcoat adhesion to canopy problem

On Feb 19, 3:42*pm, chris wrote:
Help, I have a chronic problem with my canopy. *Years ago the
plexiglass was replaced on my canopy. *Since I have owned my glider
the "white painted edge" of the canopy has been flaking off. *The
gelcoat seems to just lift off and flake away, leaving a ragged edge.
Some areas have the gel lift up into the slipstream probably not
helping the airflow.

Every year or two I mask off the edge and hand paint layers of gelcoat
back, then sand smooth and even again. *Then a few short months later,
time to do it all over again.
My new gel seems to stick better than the older stuff but even some of
what I put there has come off. *This seems to be a problem on the
overpainted plexiglass transition area and not the frame portion.

I think part of the problem is that the smooth plexiglass does not
make a good adhesion to the gel. *I also assume that there may be
differential expansion in hot/cold cycles, sun that may make the gel
and underlying plex to work apart?

So before I put on more gel, I'd love to hear some suggestions on
surface preparation or materials etc.
I have Simtec Prestec 2781 gelcoat.

I have been hesitant to really scratch/roughen up the surface of the
plexiglas, the shop before me did not do it and I would be afraid of
creating any kind of stress risers but maybe I'm just paranoid.

Should I use some kind of primer?

Chris

I had the same problem with my LS-4 canopy years ago following an
encounter with hail over Springerville, AZ. The paint aroung the
frame just peeled it back into a very ragged turbulator strip. In
contemplating the repair I realized it was important to build it back
up to the original contour so the transition to the fuselage was
even. I made sure to grind down the rough edges then I masked off the
canopy where I wanted the paint line to be. I sanded the remaining
gelcoat AND the plexiglass with 400 grit ( I think) sandpaper then
sprayed with multiple coats of gelcoat to bring everything back to
contour. If the chipping is really deep you may need to use filler
too.

Good luck.

9B