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09-16-2013, 07:35 AM
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Join Date: Feb 2010
Location: Ankeny, IA
Posts: 55
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Use a polyester primer. 2.0 tip in your gun.
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09-16-2013, 08:54 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by polishpilot
U-POL 670 Liquid Gold Pourable Glazing Putty. Google it!! It is a two part epoxy - sands extremely easy after only 20 or 30 minutes dry time.
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Jim, perhaps you should Google the difference between epoxy and polyester resin systems. U-POL 670 is just another cheap polyester product. Save it for the gel-coated polyester/glass wingtips, or your hot tub.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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09-16-2013, 10:38 AM
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Join Date: Mar 2013
Location: Flathead Lake Montana - 8S1
Posts: 334
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I've built 5 composite airplanes over the last 35 years, and helped numerous RV'ers with their glass parts. I wish there was a magic bullet for finishing glass, but the best advice I've seen coming on this board is coming from Mr Horton.
I can't tell you how many wonder products I've heard touted over the years, but if you want to see how the experts finish one-off composites go visit SCALED or the sailplane folks --- and you'll see lots of dry micro/epoxy and almost no polyester.
__________________
'83 LongEZ - N888EZ 3,671 hours
'89 LimoEZ - N26EZ 686 hours (sold)
A couple of Glasairs and a Lancair 320...
Next: a RV14 need something to build
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09-16-2013, 12:34 PM
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Join Date: Oct 2009
Location: Canby, OR
Posts: 53
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At the risk of serious rebuttale
There is really only one right way to do this and if you are at all worried about weight, you want to do this the right way. Use an epoxy filler, such as an Epoxy resin system (such as West, Aero-Poxy or Rhino) and micro-balloons if you are on a tight budget. If you are willing to spend a bit more $ to save a lot of    then get a pre-mixed epoxy filler such as Super-Fil. This will make the consistency of the surfaces to be sanded equal between filler coats.
The Van's cowlings are epoxy resin composite parts, so polyester resins (Bondo) are not really appropriate, although they have been used for COSMETIC FILLING on many a project with good results, but they need to be really small voids.
The problem I see now is that this surface has already been primed.  It needs to be sanded with 80 grit to remove the primer and then you need to try to get the primer out of the voids. Then you can start anew and fill with the epoxy filler. Fill, sand with 80 grit, then fill the spots you missed and sand with 80 then 120 grit, fill the pin holes and sand with 120 grit. Then use a sand-able high build primer. Prime, sand (120 to very thin), prime, sand (120 to very thin ), prime, sand (120, then 240). Now if you were building a composite plane, repeat for the entire exterior   .
If you have any questions, give me a call.
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09-16-2013, 12:54 PM
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Join Date: Mar 2013
Location: Flathead Lake Montana - 8S1
Posts: 334
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Quote:
Originally Posted by tfarrell839
There is really only one right way to do this and if you are at all worried about weight, you want to do this the right way. Use an epoxy filler, such as an Epoxy resin system (such as West, Aero-Poxy or Rhino) and micro-balloons if you are on a tight budget. If you are willing to spend a bit more $ to save a lot of    then get a pre-mixed epoxy filler such as Super-Fil. This will make the consistency of the surfaces to be sanded equal between filler coats.
The Van's cowlings are epoxy resin composite parts, so polyester resins (Bondo) are not really appropriate, although they have been used for COSMETIC FILLING on many a project with good results, but they need to be really small voids.
The problem I see now is that this surface has already been primed.  It needs to be sanded with 80 grit to remove the primer and then you need to try to get the primer out of the voids. Then you can start anew and fill with the epoxy filler. Fill, sand with 80 grit, then fill the spots you missed and sand with 80 then 120 grit, fill the pin holes and sand with 120 grit. Then use a sand-able high build primer. Prime, sand (120 to very thin), prime, sand (120 to very thin ), prime, sand (120, then 240). Now if you were building a composite plane, repeat for the entire exterior   .
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^^^^ Exactly right
__________________
'83 LongEZ - N888EZ 3,671 hours
'89 LimoEZ - N26EZ 686 hours (sold)
A couple of Glasairs and a Lancair 320...
Next: a RV14 need something to build
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09-16-2013, 05:18 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by tfarrell839
The problem I see now is that this surface has already been primed.  It needs to be sanded with 80 grit to remove the primer and then you need to try to get the primer out of the voids.
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Might not be a good idea to 80 grit the honeycomb at this point. It would be easy to cut the skin plies too thin over the cell walls...the high spots between the voids.
Tim, Dick, you think the voids are too deep for a high build acrylic urethane like K38?
Mike, this is block sanding a high build on a glass canopy frame. Routine stuff. See the dark streak in the lower right corner? That's the dark epoxy primer peeking through. It means I don't want to sand any further in that area.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
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09-16-2013, 08:20 PM
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Join Date: Mar 2013
Location: Flathead Lake Montana - 8S1
Posts: 334
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Quote:
Originally Posted by DanH
Might not be a good idea to 80 grit the honeycomb at this point. It would be easy to cut the skin plies too thin over the cell walls...the high spots between the voids.
Tim, Dick, you think the voids are too deep for a high build acrylic urethane like K38?
Mike, this is block sanding a high build on a glass canopy frame. Routine stuff. See the dark streak in the lower right corner? That's the dark epoxy primer peeking through. It means I don't want to sand any further in that area.

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Dan, as you know ideal situations are rarely achievable in homebuilding. Since the cowl isn't structural and Van's pre-pregs are pretty tough I'd probably block sand the affected areas (if they're regional and not endemic); and then try to dig out some of the primer with a small wire wheel in the Dremel. If 10 minutes of that didn't achieve the desired result I'd go to plan B and use K38 or something like it. If the epoxy primer in the weave could be mechanically abraded without tearing up the glass I'd go the dry micro route and then a high build epoxy primer. If the small wire wheel tears up the pre-preg than I'd go right to the epoxy primer. The key to dry micro is to wipe pure epoxy on the glass surface, wipe it all off with a paper towel , and then put LOTS of dry micro on. 95% will end up on the garage floor but this method is the best and fastest way to get perfect contours. You don't want to have to make 2 passes with dry micro as the epoxy interface between the two passes is hard and makes contour sanding much more difficult.
All of this discussion on glass surfacing is EXACTLY why, after 5 plastic airplanes, I'm going to learn to rivet via the RV-14. I'll be the one posting dumb riveting questions but I'm not at all concerned with glass. I intend to build my own wing tips from a John Roncz design and will build cowlings from scratch and layup a set in carbon pre-preg.
__________________
'83 LongEZ - N888EZ 3,671 hours
'89 LimoEZ - N26EZ 686 hours (sold)
A couple of Glasairs and a Lancair 320...
Next: a RV14 need something to build
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09-16-2013, 09:29 PM
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Join Date: May 2006
Location: Sammamish, WA
Posts: 654
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Thanks all!
The problem I showed in the picture is regional. In fact that 5x5 area I showed is the worst. The voids barely show through in some other spots, but some high build primer should cover those. There are two areas, the one I showed and the same area on the other side of the cowl, but it is not as bad there.
The information here is great though. Thank you so much.
I don't mean to shut this thread down, keep responding if you see fit. It is educational for all! I will be using what I learned here to do a better job of filling the voids on the bottom cowl.
Michael-
__________________
Michael Burbidge
Sammamish, WA
RV-14A Empennage
RV-9A Flying?340 hours!
Last Donation: December 2019
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