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  #1  
Old 09-14-2013, 11:13 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 701
Default Filling honeycomb voids

Preparing the cowl is taking me forever. The most difficult part is filling the honeycomb voids. See picture below. There's lots of information in the forums about pinholes, but I don't think the voids are pinholes. Is that correct?

How is the easiest way to fill these voids?

Thanks,
Michael-

The following pictures is after applying several coats of epoxy, sanding and applying an epoxy primer. But I still have voids in some places.

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Last edited by Michael Burbidge : 09-14-2013 at 11:41 PM.
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  #2  
Old 09-15-2013, 04:55 AM
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tkatc tkatc is offline
 
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Somebody just posted a detailed method using drywall spackling. Search for that thread and you will be a happy camper.
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  #3  
Old 09-15-2013, 05:10 AM
noelf noelf is offline
 
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The "voids" that you refer to in your picture will become pinholes once you spray on your primer. I followed Van's directions for filing the voids in the fiberglass with BONDO and shaving off the excess...it took several weeks to go over the entire cowling surface.
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  #4  
Old 09-15-2013, 05:55 AM
Smilin' Jack Smilin' Jack is offline
 
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We used epoxy AWL fairing compound, it is light weight but pretty pricey
It is a two part epoxy can be sanded easily and does the job. With out pin holes. Put it on with light coats and it can go over the primer you already shot just roughen it up with some 320 paper and clean it.
I was amazed at the number of pin holes in the fiberglass parts. But handled them with a razor blade and some Dolphin glaze.
Available from Aviall and recommended by Sam James.
Smilin' Jack

Still Painting.. 3weeks so far.
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  #5  
Old 09-15-2013, 06:48 AM
deek deek is offline
 
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Quote:
Originally Posted by Smilin' Jack View Post
We used epoxy AWL fairing compound, it is light weight but pretty pricey
It is a two part epoxy can be sanded easily and does the job. With out pin holes. Put it on with light coats and it can go over the primer you already shot just roughen it up with some 320 paper and clean it.
I was amazed at the number of pin holes in the fiberglass parts. But handled them with a razor blade and some Dolphin glaze.
Available from Aviall and recommended by Sam James.
Smilin' Jack
The AWL is a good way to go, but I think I'd scuff the primer off with 100X and then use the epoxy fairing compound. In general, it's best to not put filler on top of primer. Your cowl looks a lot better than some of the glass parts I've helped RV-4 guys with!
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  #6  
Old 09-15-2013, 07:58 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Michael Burbidge View Post
Preparing the cowl is taking me forever. The most difficult part is filling the honeycomb voids. See picture below. There's lots of information in the forums about pinholes, but I don't think the voids are pinholes. Is that correct? How is the easiest way to fill these voids?
Correct.

The traditional filler would be glass microballoons in mixed epoxy, aka "micro". You would squeegee a thin coat onto the bare glass prior to any other application, cure, sand flush, seal with a few unthinned epoxy coats, sand again, then shoot primer.

BTW, AwlFair LW 8200/7200 is fundamentally the same thing, but premixed and 10x more expensive. Take a look at the MSDS and tech sheet...bisphenol A epoxy, glass and phenolic bulk fill. Same is true of PolyFiber's SuperFil.

Quote:
The following pictures is after applying several coats of epoxy, sanding and applying an epoxy primer. But I still have voids in some places.
I'm guessing you thinned the epoxy? Several coats of of unthinned West should have built up enough to fill the honeycomb depressions, even without micro. Still, it does look like you got it sealed, no pinholes, at least as well as I can tell in a photo.

The question is what to do now. You need a process which will work over the epoxy primer. Sanding to remove the primer won't really work, as you would still have primer down in the depressions.

First, your epoxy primer probably has a recoat window. Don't let it expire. If necessary shoot another coat within the previous coat's window.

PPG, SW, etc, all have high-build primer/surfacers. They are generally talc (the filler) in an acrylic binder. Primer/surfacers are intended to be sprayed over fresh epoxy primer. The idea is to spray on a heavy coat, cure, then block sand to remove all the filler from the high places, leaving it to fill the lows. It will take a few rounds, but this is work that a good painter would do anyway, and it can be sanded for tooth and painted later without restriction.

In PPG, look for K36 or K38.
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  #7  
Old 09-15-2013, 05:07 PM
Michael Burbidge Michael Burbidge is offline
 
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Location: Sammamish, WA
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Default Followup question...

Thanks all for the responses.

So Dan on the other half of the cowl, I will start with micro-balloons. I've used that in other places to do buildup. Then I assume after the voids are filled and smoothed, a few applications of epoxy, followed by an epoxy primer.

What consistency is best for filling these voids?

Thanks,
Michael-
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  #8  
Old 09-15-2013, 05:22 PM
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Vlad Vlad is offline
 
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I hear you Michael I put four coats of West System epoxy. What a pain to sand boy.


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  #9  
Old 09-15-2013, 08:41 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Michael Burbidge View Post
So Dan on the other half of the cowl, I will start with micro-balloons. I've used that in other places to do buildup. Then I assume after the voids are filled and smoothed, a few applications of epoxy, followed by an epoxy primer.
You'll sand off all of the micro, leaving only what remains down in the voids.

Quote:
What consistency is best for filling these voids?
Whatever works. I'd suggest peanut butter.
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  #10  
Old 09-16-2013, 07:29 AM
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polishpilot polishpilot is offline
 
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Default Use UPO-670

U-POL 670 Liquid Gold Pourable Glazing Putty. Google it!! I purchased mine through Amazon.com. Or get it direct from TCP Global. It is a two part epoxy - sands extremely easy after only 20 or 30 minutes dry time. Super great for filling these pinholes.. Van's method of acetone and epoxy resin is fine for the INSIDE of the cowl, but not the outside. As someone mentioned it is too hard to sand.
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