Gelcoat adhesion to canopy problem

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

First mask off the canopy inside and out.
remove remaining Gelcoat, sand vigorously with 180 grit paper.
Brush off plexi glass dust, wipe with alcohol.
Use small spray gun and spray either Gelcoat or Poly Urethane.
If you use Gelcoat you need an additive which make it more flexible and
paint like. Urethane can be sprayed as is.
Keep the layer as thin as possible just enough to cover any dark spots.
Udo

At 23:42 19 February 2009, 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

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

On Feb 19, 4:30*pm, Udo Rumpf wrote:
First mask off the canopy *inside and out.
remove remaining Gelcoat, sand vigorously with 180 grit paper.
Brush off plexi glass dust, wipe with alcohol.
Use small spray gun and spray either Gelcoat or Poly Urethane.
If you use Gelcoat you need an additive which make it more flexible and
paint like. Urethane can be sprayed as is.
Keep the layer as thin as possible just enough to cover any dark spots.
Udo

At 23:42 19 February 2009, 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?

Yep, Udo is right! You have no adhesion, remove all the old then sand
the plexy till all the shiny is gone. I use 220 on the outside and 40
grit on the inside when replacing a canopy. Don't worry about creating
stress risers. Carefully mask with good tape (I like the blue stuff
from automotive paint stores) because you can make good tight curves
and it leaves a clean paint line. Carefully sand right up to the
masking line, paint and wet-sand with a small block( 600W then 800W)
right over the masking tape till the paint depth = the masking tape
depth, Then buff before removing the tape for a crisp professional
looking job.
Cheers,
JJ


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- Hide quoted text -

- Show quoted text -

Good feedback so far. Just to clarify: I'm just trying to do spot
repairs, [at least right now for this season]. The gel is chipping
off in small pieces the size of a, grain of rice, fingernail clipping
to the size of a full fingernail/small coin. So I don't think
spraying makes sense. Getting sandpaper into the spot is difficult
because some areas are no wider than they are deep, and you have to be
careful to not scratch the main clear part of the canopy that is
directly adjacent.

The chips are the full thickness / single layer of gel. It is about
as thick as 2-3 pieces of paper.

Maybe I should consider next year having it all stripped down, all the
gel removed and a totally redone, right now I just need to get patched
for the spring.

If I put primer on the plexiglass, would gelcoat adhere to a layer of
paint primer?

Chris

On Feb 20, 3:58*am, chris wrote:
Good feedback so far. *Just to clarify: I'm just trying to do spot
repairs, [at least right now for this season]. *The gel is chipping
off in small pieces the size of a, grain of rice, fingernail clipping
to the size of a full fingernail/small coin. *So I don't think
spraying makes sense. *Getting sandpaper into the spot is difficult
because some areas are no wider than they are deep, and you have to be
careful to not scratch the main clear part of the canopy that is
directly adjacent.

The chips are the full thickness / single layer of gel. *It is about
as thick as 2-3 pieces of paper.

Maybe I should consider next year having it all stripped down, all the
gel removed and a totally redone, right now I just need to get patched
for the spring.

If I put primer on the plexiglass, would gelcoat adhere to a layer of
paint primer?

Chris

Just put some tape over it.

On Feb 19, 6:58*pm, chris wrote:
Good feedback so far. *Just to clarify: I'm just trying to do spot
repairs, [at least right now for this season]. *The gel is chipping
off in small pieces the size of a, grain of rice, fingernail clipping
to the size of a full fingernail/small coin. *So I don't think
spraying makes sense. *Getting sandpaper into the spot is difficult
because some areas are no wider than they are deep, and you have to be
careful to not scratch the main clear part of the canopy that is
directly adjacent.

The chips are the full thickness / single layer of gel. *It is about
as thick as 2-3 pieces of paper.

Maybe I should consider next year having it all stripped down, all the
gel removed and a totally redone, right now I just need to get patched
for the spring.

If I put primer on the plexiglass, would gelcoat adhere to a layer of
paint primer?

Chris

I had the same problem. The issue for me was that much of the gelcoat
was not bonded to the plex, even if it hadn't chipped yet so spot
fixes were going to be an ongoing, time-consuming process. Gelcoat
doesn't bond well without some surface area, so you are talking about
sanding down an area around each chip that may be larger than the chip
itself, adding new gelcoat, then sanding and polishing the whole thing
without sanding through anywhere and without scratching the canopy. In
the process of doing this you could easily make new chips and in any
event new ones will appear in un-repaired areas. In my case I just
covered the border with wing tape until I could do a proper job.

9B

Yep, 9B is right. Cover it with wing tape until you can do it right. I
did a ASH-26 last year with the same problem. As I tried to get the
loose stuff off, more started chipping off, ended up flipping most off
with a razor blade. It looked like Schleicher used 600 grit which
isn't nearly rough enough. Water works its way under the edge and away
it goes.
JJ


On Feb 20, 5:00*am, wrote:
On Feb 19, 6:58*pm, chris wrote:





Good feedback so far. *Just to clarify: I'm just trying to do spot
repairs, [at least right now for this season]. *The gel is chipping
off in small pieces the size of a, grain of rice, fingernail clipping
to the size of a full fingernail/small coin. *So I don't think
spraying makes sense. *Getting sandpaper into the spot is difficult
because some areas are no wider than they are deep, and you have to be
careful to not scratch the main clear part of the canopy that is
directly adjacent.

The chips are the full thickness / single layer of gel. *It is about
as thick as 2-3 pieces of paper.

Maybe I should consider next year having it all stripped down, all the
gel removed and a totally redone, right now I just need to get patched
for the spring.

If I put primer on the plexiglass, would gelcoat adhere to a layer of
paint primer?

Chris

I had the same problem. *The issue for me was that much of the gelcoat
was not bonded to the plex, even if it hadn't chipped yet so spot
fixes were going to be an ongoing, time-consuming process. Gelcoat


doesn't bond well without some surface area, so you are talking about
sanding down an area around each chip that may be larger than the chip
itself, adding new gelcoat, then sanding and polishing the whole thing
without sanding through anywhere and without scratching the canopy. In
the process of doing this you could easily make new chips and in any
event new ones will appear in un-repaired areas. In my case I just
covered the border with wing tape until I could do a proper job.

9B- Hide quoted text -

- Show quoted text -