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  #1  
Old 09-28-2022, 12:45 PM
mfleming's Avatar
mfleming mfleming is offline
 
Join Date: Sep 2016
Location: Joseph, Oregon
Posts: 989
Default Primer on Fiberglass Fix?

Recently I sanded and primed my cowling with a 2K epoxy primer. Apparently I was over aggressive when sanding. The fiberglass cloth weave is showing on a fair amount of the cowl.

My paint shop told me "rough sand the fiberglass and apply a 2K primer and they will make it pretty". So, really the primer is acting as a sealer until it gets to the paint shop. Protection from oil and dirt....

My concern is, do I need to do something to preserve the integrity of the primer as a sealer or is it protected from contamination as is?
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Michael Fleming
Joseph, OR
sagriver at icloud dot com

RV-7 Slider #74572
Started 11/2016
Empennage completed 11/2016
Ailerons and flaps completed 3/2017.
Wings completed 12/2017
Started on QB fuselage 01/2018
Sliding canopy mostly completed 10/2020
Wiring and Avionics harness completed 9/2/2021
FWF Completed 11/1/2022
Final assembly Started 11/10/2022
Wings on 11/12/2022

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  #2  
Old 09-28-2022, 12:57 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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Default

You were not ready for prime. Much more body work needs to happen. I suggest you work it out with your paint shop on who will do what. If they are doing the body work they will again sand. I suspect you can just light sand and shoot another coat or two of primer if you have bare spots.

Not familiar with 2K primer. Is it UV resistant?

Carl
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  #3  
Old 09-28-2022, 01:10 PM
PhatRV PhatRV is offline
 
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Location: KAJO
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Quote:
Originally Posted by mfleming View Post
Recently I sanded and primed my cowling with a 2K epoxy primer. Apparently I was over aggressive when sanding. The fiberglass cloth weave is showing on a fair amount of the cowl.

My paint shop told me "rough sand the fiberglass and apply a 2K primer and they will make it pretty". So, really the primer is acting as a sealer until it gets to the paint shop. Protection from oil and dirt....

My concern is, do I need to do something to preserve the integrity of the primer as a sealer or is it protected from contamination as is?
I have a lot of pinholes when I primed the fiberglass parts. I was successful at using the high build primer which is layed up thicker than the regular epoxy primer. Then you sand down most of it away. The high build primer covers up all of the tiny pinholes and sanding imperfections. Then you can spray epoxy primer on top of the surface to seal it or just spray paint on top.
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  #4  
Old 09-28-2022, 01:11 PM
mfleming's Avatar
mfleming mfleming is offline
 
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Location: Joseph, Oregon
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Quote:
Originally Posted by Carl Froehlich View Post
You were not ready for prime. Much more body work needs to happen. I suggest you work it out with your paint shop on who will do what. If they are doing the body work they will again sand. I suspect you can just light sand and shoot another coat or two of primer if you have bare spots.

Not familiar with 2K primer. Is it UV resistant?

Carl
You're very correct about not being ready for primer as far as final paint goes. This primer is really just protection from oil and dirt until the AC reaches the paint shop.
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Michael Fleming
Joseph, OR
sagriver at icloud dot com

RV-7 Slider #74572
Started 11/2016
Empennage completed 11/2016
Ailerons and flaps completed 3/2017.
Wings completed 12/2017
Started on QB fuselage 01/2018
Sliding canopy mostly completed 10/2020
Wiring and Avionics harness completed 9/2/2021
FWF Completed 11/1/2022
Final assembly Started 11/10/2022
Wings on 11/12/2022

N526RM

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  #5  
Old 09-28-2022, 03:45 PM
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PaulvS PaulvS is offline
 
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The surface in the photos appears porous so contamination will likely get in.
It doesn't look like the primer has sealed because the surface was too rough for primer.
Probably a brushed on coat of epoxy resin would've been a better sealer if the shop is going to do the bodywork filling and block sanding.
As to the fix now, like Carl says it would be best to talk to the paint shop but I think it will need filling before sealing.
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Last edited by PaulvS : 09-28-2022 at 03:53 PM.
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  #6  
Old 09-28-2022, 05:10 PM
Bandera Bandera is offline
 
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Location: Gainesville, Tx
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No worries with the primer but now there is work to be done. What you can see now is where every pinhole and void is located. Fill them, sand it smooth and prime again. If there are no pinholes this time, sand it smooth and paint. If there are pinholes, fill again and prime. Sand it smooth and paint.

A complete set of fiberglass parts takes me 2.5 days start to finish.
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  #7  
Old 09-28-2022, 06:24 PM
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wirejock wirejock is offline
 
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Location: Estes Park, CO
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Default Fiberglass prep

I am a hack, but I get really lucky.
Dan Horton method with minor deviations. I spread micro, sand flat then a coat of neat epoxy. Sand that flat then two brushed coats of 2K epoxy primer. Wet sand that flat and there's almost nothing left to seal. The parts look like heck but they are smooth as a baby's bottom. At that point I shoot primer. If there are any imperfections, they get a tiny smush of glazing before the final paint.

Honestly, I think it's fine if you patch the area with some 2K primer. That's what the paint shop recommended. They will sand it anyway.
Again, I know nothing!
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  #8  
Old 09-28-2022, 07:02 PM
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DanH DanH is offline
 
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What Carl said. The surface was nowhere near ready for an epoxy or urethane primer.

I'd sand off all the primer, back to bare glass, roll or brush a coat of System Three ClearCoat (or a similar water viscosity pure epoxy) to fill and seal, scuff sand when cured (without breaking through!), then shoot epoxy primer followed by a high build primer as soon as the epoxy primer's solvents flash off. Block sand for flatness.
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  #9  
Old 09-28-2022, 07:30 PM
mfleming's Avatar
mfleming mfleming is offline
 
Join Date: Sep 2016
Location: Joseph, Oregon
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I appreciate everyones input.

The reason for applying the epoxy primer is not for final paint...it's sole function is to protect the fiberglass from oil and dirt until it makes it to the painters...they'll sand it off and do whatever it takes to make it pretty.

My question was/is, do you think what's on there will protect it from oil/dirt?

And since my original post, I sprayed another coat of primer...
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Michael Fleming
Joseph, OR
sagriver at icloud dot com

RV-7 Slider #74572
Started 11/2016
Empennage completed 11/2016
Ailerons and flaps completed 3/2017.
Wings completed 12/2017
Started on QB fuselage 01/2018
Sliding canopy mostly completed 10/2020
Wiring and Avionics harness completed 9/2/2021
FWF Completed 11/1/2022
Final assembly Started 11/10/2022
Wings on 11/12/2022

N526RM

Donated for 2022 and so should you
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  #10  
Old 09-28-2022, 07:51 PM
Bandera Bandera is offline
 
Join Date: Feb 2021
Location: Gainesville, Tx
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Quote:
Originally Posted by DanH View Post
What Carl said. The surface was nowhere near ready for an epoxy or urethane primer.

I'd sand off all the primer, back to bare glass, roll or brush a coat of System Three ClearCoat (or a similar water viscosity pure epoxy) to fill and seal, scuff sand when cured (without breaking through!), then shoot epoxy primer followed by a high build primer as soon as the epoxy primer's solvents flash off. Block sand for flatness.
No reason to back to bare unless the the surface was never sanded.
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