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Old 01-17-2019, 06:25 PM
scorkey scorkey is offline
Join Date: Jun 2018
Location: Bonaire, GA
Posts: 5
Question Chip/voids in fiberglass fairing gelcoat

While notching the Horizontal Stabilator Fairings, a small area of gelcoat adjacent to the fiberglass flange cracked and flaked off leaving a chip all the way down to the glass cloth. I also uncovered some voids in the gelcoat in the trailing edge of the fairing after sanding down the factory seam.

Being new to fiberglass, Iím wondering if these defects need to be addressed now - and if so, how. Or whether surface defects like these will be filled and resolved in the normal process when prepping the aircraft for paint.
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Old 01-17-2019, 06:59 PM
David Paule David Paule is offline
Join Date: Dec 2009
Location: Boulder, CO
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If it were mine, I'd do all my glass work together. That way, I'd have fresh epoxy and materials at hand. I'd just plan on an epoxy-microballoon paste for filling them.

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Old 01-17-2019, 08:40 PM
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Dvalcik Dvalcik is offline
Join Date: Jul 2011
Location: Ellsworth, ME
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Originally Posted by David Paule View Post
If it were mine, I'd do all my glass work together. That way, I'd have fresh epoxy and materials at hand. I'd just plan on an epoxy-microballoon paste for filling them.

+1 I agree
Belfast, ME
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Old 01-18-2019, 08:01 AM
benfra benfra is offline
Join Date: May 2007
Location: ft MYERS, FL Based @KPGD
Posts: 22
Default Filling Fiberglass Voids

I would make sure there is fiberglass structure remaining, If so try to rough up the hole,with sand paper or sharp pointed tool. This will ensure the filler will adhere, then fill with microballoon epoxy mix. As you know the micro and epoxy has little strength without fabric. N80EZ long eze. 1988 If its on an edge you probably should use FLOX a mixture of cotton fibers and epoxy, its very strong, but harder to sand .

Last edited by benfra : 01-18-2019 at 08:14 AM. Reason: added content
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Old 01-18-2019, 08:05 AM
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N941WR N941WR is offline
Join Date: Jan 2005
Location: SC
Posts: 12,161

Check your EAA chapter, someone must have experience with fiberglass and can help you out.

Someone once told me, "Think of fiberglass as being like drywall. If you mess it up, you can cut it out and redo it "

Good luck. I agree with the others and suggest you wait.
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
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Old 01-18-2019, 12:37 PM
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DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 8,547

Originally Posted by benfra View Post
As you know the micro and epoxy has little strength without fabric.
It's not a structural material. However, I'd encourage builders to make up a few test lumps, cure them, and break them just to get a feel for practical strength as a filler material. It ranks very high on that scale.

Unless things have changed, those emp tips are polyester glass and gelcoat. A little dab of ordinary polyester-based filler will fix minor defects. It's fast and cheap.

Do not depend on a paint shop to fix anything unless you've made very specific arrangements regarding paid labor time. In general, you're always better off to deliver an aircraft truly ready for paint, every surface and edge finished and ready.
Dan Horton
Barrett IO-390
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Old 01-18-2019, 12:55 PM
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Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
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Default Welcome to VAF

Scott---Welcome aboard

If the parts are gel coated, they are most likely polyester not epoxy.

Regular Bondo is a good choice, or auto body glazing putty if the divot is small.
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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Old 01-27-2019, 02:47 PM
Charlie12 Charlie12 is offline
Join Date: Oct 2014
Location: Port Orange FL
Posts: 21
Default filling small voids

The voids in your photos are structurally insignificant and can be filled pretty much any way you like. After years of teaching college students how to do this kind of stuff, I developed a preference for Bondo. It is a 2-part polyester paste that you can get at any auto parts store. It cures really quickly, so you can sand it within a few minutes and be done with it. Micro-balloons or cotton flox are fine and are preferred by lots of people. You mix them into laminating resin until you get a paste approaching the consistency of toothpaste. Many newcomers make it too runny and it sags out of the hole before curing. These two materials are probably stronger than Bondo but take more time to mix up and strength is not really a concern in this instance.

Most of the strength of composite parts is in the fabric so if you cut or scratch into the glass fabric plies there is a strength issue and any patching needs to be done much more carefully. I'd find a local tutor for that. There are lots of them around.
RV-12 #120768, first flight Sept. 2016
180 hrs as of 1/1/2019
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Old 01-27-2019, 11:01 PM
lr172 lr172 is online now
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,010

To add to this, all f/g parts should be checked for suspicious looking areas of fiberglass. I find the older Van's f/g parts to be pretty poor in overall workmanship (newer stuff seems better). Anything that looks out of the ordinary gets probed with a dental pick. Often, I find a VERY thin outter layer of resin with an air pocket under it. The OP's first pick is a good example of this. Likely there was a thin outer layer of resin not bonded to the laminate below. It is not a gel coat failure. It is the fabricator allowing an air bubble in the layup and this is most likely to happen at the raised corner of the joggle. If you don't identify this and fill them, they are likely to appear years down the road, after you have painted. Most problems are around edges, joggles, sharp outer corners, etc. This is arguably much more difficult to find the defects with the gel coated parts. Tapping with a screwdriver handle can also help identify the air pockets.

RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress

Last edited by lr172 : 01-27-2019 at 11:12 PM.
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