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Fillers

Av8torTom

Well Known Member
I have a couple of small dents in my project that are driving me nuts to look at and I?m looking for recommendations on fillers. While I intend to paint, something close to aluminum color would be preferable.

Thanks
 
Flexible

I'm afraid epoxy and micro would not be flexible enough.

Anyone have experience with SuperFil?

09-28250-ab-kit.jpg
 
I haven?t yet tried it

But SuperFil was recommended to me by previous RV builders. They used it in their planes (now flying).
 
Superfil is basically pre mixed epoxy and micro balloons. Great stuff but not flexible as it cures very hard.
 
Another approach to the problem...

I just notice a couple of small dings on the top surface of my right wing. I considering these or something similar as at least a temporary fix...
 
The fundamental choice is epoxy resin base or polyester resin base. Given a suitably prepared surface (freshly sanded and cleaned), either will stick to aluminum. The epoxy out-sticks the polyester. Either is flexible enough, if not applied too thick.

The solids added to the resin base can be microballoons (glass or phenolic, i.e white or reddish brown), talc, ground plastic, wood flour, and/or a whole bunch of other stuff. Pre-mixed products generally claim some special recipe (such is commerce), but consulting the MSDS will offer a clue as to what is really in them.

Microballoons and talc are the most common. Micro (hollow spheres) adds bulk with little weight. Talc is heavier for a given volume, but sands smoother.

I tell you all this because a builder can easily mix whatever he likes.
 
Funny

I just notice a couple of small dings on the top surface of my right wing. I considering these or something similar as at least a temporary fix...

Thanks for the chuckle Miles.

Thanks everyone for your inputs.
Yes, I know very well the properties of thickened epoxy mixtures, and I could easily mix-up something of my own (I don't think I'd consider the saw dust approach however :D). I was hoping there was something out there I didn't know about that might be a bit more flexible. Maybe it's just not an issue.
 
How big are the dents?

It amazing how minor defects disappear as the build gets bigger. If the dents are small I'd leave them alone. Filler adds weight, attracts the eye and will eventually crack and flake off.

I struggle to find the dings that bugged me during the build and no one else even notices them. I'd leave the metal alone unless it's really bad.

I did pin-hole fill the fiberglass before paint.

Just my 2 cents.

Jim Sharkey
 
How about just metal glaze, something like this Evercoat 425 Metal Glaze Ultra

Good example of a polyester-base filler. Should be fine.

Polyesters shrink, so consider epoxy for more than a thin wipe.
 
I used Evercoat Rage (polyester filler) with good success on my plane. This is a premium filler that adheres and sands better than straight bondo and cheap fillers. 500 hours and no issues. These fillers stick well to aluminum if prep'ed properly (sand, not scuff, and cleaned very well) and I find them easier to work with than epoxy, but I have done a good bit of auto body work so familiar.

Larry
 
I'm afraid epoxy and micro would not be flexible enough.

Straight epoxy/micro will be plenty flexible and won't ever come off. For strongest bond, expose bare aluminum shortly before application (minutes) using sandpaper, or chemical etch with phosphoric acid. (Home Depot sells phosphoric acid in glycol for half the price of AS&S; they call it "Prep & Etch".)

Having said that, I made a bit of a mess when epoxy/micro dripped onto uncleaned oxidized aluminum while I was glassing in pieces of canopy. That reminder has been sitting there on thin fuselage skin for about five years unprotected; no signs of it ever coming off despite all my wishing. I also filled in some pop rivets with bondo: none ever fell out, also unprotected.

If you are really paranoid about flexing, thin the epoxy/micro mixture with 5% acetone and spray, that way you'll end up with shorter chains resulting in much weaker, more flexible polymer:

https://epoxyworks.com/index.php/thinning-west-system-epoxy/

Or simply use J-B Weld, which is a 3-4000 psi mixture with etchant, and nice matching color to boot! Heavier though.

Your biggest problems with epoxy/micro will be: it keeps sagging after application to vertical surfaces (use lots of fast activator, work fast) and, it takes quite some effort to sand because it cures so hard. Cracking and pieces falling off aren't on this list. ;)
 
If you are concerned about flexibility or adhesion use West system G-flex resin . It was developed to bond to dissimilar surfaces and specifically aluminum. It never gets supper hard and is used in the boating industry to repair aluminum Boats. You can mix micro ballons with it and get a really good filler. the more Micro you use the easier it is to sand. If it gets stiff while applying just run a heat gun over it and you can really smooth it out.

It comes in two flavors, Thickened which is what I mostly use and normal which is about the consistency of normal west epoxy. Just make sure you really prep the area well clean clean clean and rough the area up. I would probably used the thin stuff to make a filler.

When I built my 8 we used to attach the piano hinges on the Cowl. I did a test piece and challenged visitors to tear it apart. Its still in one piece. The really big deal is that it has enough elasticity to withstand temp changes.

I think there is a Youtube video showing a patch made with Gflex being applied under water. pretty amazing .
 
I have some on my motorcycle but I never thought of putting them on my plane(bullet hole stickers)....Awesome!
Just ordered some from amazon.
 
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