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  #11  
Old 01-19-2022, 11:22 PM
BJohnson's Avatar
BJohnson BJohnson is offline
 
Join Date: Jun 2005
Location: Federal Way, Wa
Posts: 280
Default Looking back at the photo

The bubbles are only over the honeycomb core, and not over the solid laminate, which supports the idea that air is being forced out of the core cells if heated.
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  #12  
Old 01-20-2022, 06:29 AM
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Location: 08A
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Default

Quote:
Originally Posted by wirejock View Post
Ever seen a cowl go through puberty and get some serious acne zits? Click on the photo and zoom.
I've never seen anything like that...except when warming wet micro to make it flow, rarely a good idea.

Micro is for contour. Contouring (shaping ) should be long gone done before any applications of neat epoxy. Heck, micro brings new pinholes to the party, as it almost always traps some tiny air bubbles during mixing, and the glass bubbles themselves are hollow. Sand them open and each forms a microscopic pinhole.

In order:
1. bare glass structure
2. dry micro, block sanded to bring contour within a few thousandths of the desired surface profile.
3. neat epoxy to seal the surface, sanded just enough to remove drag marks and orange peel. Do not break through.
4. Two cross coats of a good epoxy primer. Use a color which will contrast with the next material, which for something like a cowl is...
4. Acrylic urethane high build primer surfacer, sprayed before the epoxy primer crosslinks. Block sand wet. This is where the surface becomes optically flat...no waviness to be seen in the finished, painted surface. Block until the contrasting epoxy primer starts to show through the high spots. If still bridging lows, shoot two more cross coats and sand again. Repeat until perfect.
5. Now it ready for paint, or the paint shop.

Blocking high-build requires fewer rounds if the earlier micro work was done right, and it takes less micro if the structural glasswork was done right, which usually means time spent on perfect forms and molds is time well spent.

Note acrylic urethane high build, not polyester. Polyester primer-surfacers were once the body shop standard, and there is a lot of it still used when cheap and fast are priorities. It very often does not stay stuck on epoxy glass, in particular the concave places, the only variable being how long it takes...months or years. Shrinkage and big blisters where it releases. The VariEze guys lived that one years ago. No point in re-inventing the square wheel.
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  #13  
Old 01-20-2022, 09:06 AM
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wirejock wirejock is offline
 
Join Date: Oct 2005
Location: Estes Park, CO
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Default Tips

Thanks for the tips.
This stuff will be sanded off today and I'll try again.
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wirejock at yahoo dot com
Donated 12/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (3,000+ hours)
Empennage, wings, fuse, finishing kit done. Working FWF
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I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #14  
Old 01-20-2022, 09:14 AM
abwaldal@gmail.com abwaldal@gmail.com is offline
 
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Location: Battle Ground WA
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Default School of hard knocks

People ask me where I learned all the stuff I know.
Welcome to the "school of hard knocks".
Been there done that. I did laugh and cringed cause I hate glass/epoxy pimples.
Everything looked so right and then Bam it isn't.
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  #15  
Old 01-20-2022, 03:31 PM
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wirejock wirejock is offline
 
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Location: Estes Park, CO
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Default Popped the pimples

Seems like there's a show about popping pimples. Ok. Joking aside.
Pimples have been popped. Top cowl is sanded. Huge job I do not want to repeat.

What should I do next?
I think a new application of micro on one section is a good test. I don't want to sand the whole thing off again if it doesn't go well. Sand the micro to shape then skim with neat epoxy to seal.

Any input appreciated.
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Larry Larson
Estes Park, CO
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Donated 12/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (3,000+ hours)
Empennage, wings, fuse, finishing kit done. Working FWF
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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