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Covering pin holes in the fiberglass cowling & fairings.

V

vickytori

Member
We are having trouble filling the pin-holes in the fiberglass. Using a poly fiber and having to sand, reapply it and sand. Still not covering the holes. Any ideas?
 
Mix a slurry of resin and micro balloons then spread thinly it over the surface with a spreader to fill in the holes. Sand to finish.
 
As a plastic plane owner of several years I have researched this a lot. Featherfill does not have a lot of happy long term users:

"....using that absolutely crappy Feather Fill. Get a paint chip where water can get in and the Feather Fill soaked it up like a sponge. Later the nightmare. Bubbles inder the paint starting at 2" and up to 10" Constantly chasing the fixes until the paint surface is a combination of unfixed primer or mismatched paint blotches."

Straight epoxy seems to be the best pin hole filler. Has been used by canard builders for years now with excellent results since Cory Bird perfected it with his award winning Symmetry:
http://www.air-and-space.com/20090815 Mojave/BL2_8798 Cory Bird Symmetry N241ST left front l.jpg

He knows a thing or two about composites in case that picture didn't convince you.......:
01/31/2013
SCALED COMPOSITES ANNOUNCED TODAY THAT IT HAS NAMED KEVIN MICKEY PRESIDENT AND CORY BIRD VICE PRESIDENT, EFFECTIVE IMMEDIATELY. .

Warm it with a hair dryer as you squeegee it on and it will fix most of them. Anything else, like more micro or primer, will bridge them and sanding can open them back up. An exception may be the powder product by those guys that have their own paint system and sell little replica airplane kits. Have not heard anything bad about their pin hole filler. I think your RV composite guru, Dan, will have some good advice too.

See:
http://www.canardcommunity.com/showthread.php?t=1514&page=5

Remember to focus on advice from those painted and flying for a few years as they will have seen the results of their process by then! The bad ones will have shown up after time......
 
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I use an automotive microfiller (red) that I purchased at my local body shop supplier. Works great. Squeegee it in the holes, let it dry thoroughly and then dry and wet sand with 400/600 sandpaper. I did this after priming with sandable k36? primer.
 
Squeegeed (is that a word?) on clear epoxy, sanded back off, three times. Time consuming but it worked. Wish there was an easier way, but if there is I never found it!
 
+1 for Clear Epoxy

Tried a number of methods without success and went for the clear epoxy (not thinned) and a small (about 3 inch) squeegee. Trick was to remove the majority of the epoxy with the sgueegee, did this three times with sanding between coats. If I remember correctly the process is described on the West Systems web site.
 
I will fly for six months or so and then have the plane painted. Should I worry about filling pinholes prior to flying or let the painter handle it?
 
pin hole filling

The quickest and EZist is use the lacquer based red spotting putty. It can be worked into the holes using a putty knife, dries fast and easily sanded. Once filled out, then respray the entire part with sandable primer/filler and wetsand with 400 grit. Don't use the spotting putty for filling defects, just pin holes.

I wouldn't advise using epoxy to fill holes because you can still trap air in the hole and it's really hard to sand.

Featherfill will work fine for filling out raw fiberglass weave, but it leaves a lot of pin holes because it's thick and sprayed. Some people have had issues with bonding years later, but I suspect it was more related to inadequate fiberglass prep. I used it on my Long-EZ and had no issues at 22 yrs out. After West Systems filling system came out, Rutan used that instead of Featherfill.

I don't know that it matters if a person finishes out to perfect primer before flying with intent of painting much later. Either way, it will have to be throughly sanded and cleaned before painting.

My 2 cents....
 
Flyingriki,

I had the plane about 4 yrs after using feather fill and didn't have any issues, but I live in Arizona. I have no experience with feather fill in wet climates.

Rich,
 
I started out using the red filler from the auto store too, the stuff I had used on car repairs for years. When my very knowledgeable paint man discovered what I was doing he was horrified! Said the red stuff was incompatible with the epoxy and would eventually separate from it. Maybe he was right, maybe not, but why take a chance? So I decided to stay with the two part epoxy as recommended by West and Dan Horton. More work, but probably safer for the long run. JMHO
 
Fill first, then fly

Tom,
I would fill the holes before flying. I did and was very pleased. It took some work using Superfill, West Systems epoxy and then a light grey primer. My painter was pleased because his concern was any oil getting into the fiberglass will cause problems later on. I also skim coated the inside of the cowling with epoxy for the same reasons.
 
RFSchaller said:
Flyingriki,

I had the plane about 4 yrs after using feather fill and didn't have any issues, but I live in Arizona. I have no experience with feather fill in wet climates.

Rich,
Click to expand...

I think you may have been lucky. There was a lot of discussion about it on the canard forums and many had issues that were not due to prep. Best to stick with all epoxy products according to the most experienced builders. Why chance it?
And I saw Symmetry at Mojave a few months ago, looks as good and the day he won at Osh. He taught us all a lot about finishes!
http://www.homebuiltairplanes.com/f...hnology/6092-cory-birds-symmetry-details.html
 
Kentsrv7a said:
Tom,
I would fill the holes before flying. I did and was very pleased. It took some work using Superfill, West Systems epoxy and then a light grey primer. My painter was pleased because his concern was any oil getting into the fiberglass will cause problems later on. I also skim coated the inside of the cowling with epoxy for the same reasons.
Click to expand...

Thanks Kent! I have added it to my list of the final things to do. Ready to fly in about two months. I have already used thinned epoxy resin on the interior.
 
Lazy or efficient??

Hey fellas:

I have tried a few methods, but none are what I would call EASY.

Here's what I do:
Sand with 220 or so, and wipe with a DRY paper towel.
DO NOT blow the dust off - it is filling all the holes.
Spray with K36 - not too much. You can use a roller if desired.
sand again to fill the remaining holes
spray or roll again; sand
The holes should be filled & covered.
You can dab or squeegee K36 into any remaining holes
Remember that K36 (and other sprayable filler/primers) will cover 36 grit scratches, so don't be too kind when sanding.

Using straight resin is doable, but the parts have to be heated to over 100F to get the resin to kick off. Not all resins will stand for thinning - be careful with this part. I saw it done at the NXT shop in SLO, CA - it worked fine. Sanded with 150 grit between coats - I think 5 were required. LOTS of hand work.

Good luck with this pinhole thing - I don't think there is a shortcut.

Carry on!
Mark
 
+2 epoxy

I thought the epoxy and squeegee worked the best for filling pinholes. I read it in some Vans instructions somewhere. Three light coats squeegeed in was enough for mine.
 
I used the epoxy resin only method, which I read off of a Cozy builders website. I figured who better to follow than someone who has an entire aircraft of pinholes to fill. The suggested method was to brush on a coat of resin and let it set for a bit, then use a credit card or squeegee and scrap off all of the excess. This worked on my cowl like a champ. I figured if plain resin would not flow into and fill the pinholes, then how on earth would resin that was thickened with any media be able to get inside of a pinhole?
 
Flyingriki,

I used the feather fill on a WAR FW-190 project. One of the nice things about it was that since it was white you always knew when you had sanded the black auto paint primer too much!

Rich
 
curtis said:
I used the epoxy resin only method, which I read off of a Cozy builders website. I figured who better to follow than someone who has an entire aircraft of pinholes to fill. The suggested method was to brush on a coat of resin and let it set for a bit, then use a credit card or squeegee and scrap off all of the excess. This worked on my cowl like a champ. I figured if plain resin would not flow into and fill the pinholes, then how on earth would resin that was thickened with any media be able to get inside of a pinhole?
Click to expand...

Good logic. And using a hairdryer instead of altering the correct ratios or contaminating the epoxy with solvents makes it run thinner and fills them just fine. Other suggestions that leave air in them are just asking for problems with big temp changes and time. It's all been documented by those that know.
It sounds like warm, dry climates are most forgiving of these variations from the proven systems, like Mojave and Arizona.....
 
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