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Micro balloons vs Colloidal Silica

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davdue

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I am building a fiberglass (Rocketry Warehouse 38 special) for my son. He hates to build them but loves to fly them. He has his L1. I have ran out of colloidal silica. I bought some micro balloons a long time ago and have never used them. Could I use that in my West Systems 105 for the internal and external fillets? Or should I use some Aeropoxy ES6209. I have never used it. I have some I won in a volunteer raffle at AirFest a couple years ago.
 

MikeyDSlagle

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Micro balloons lower the density of the epoxy and (I think) makes it easier to sand - which would make it softer maybe. Not sure.

With that rocket you should be fine with the micro balloons. Some folks that's all they use. Unless you are saving the gold filled Aeropoxy for a super tough build, why not use it?. It is a structural epoxy after all. I've never used it myself though.
 

davdue

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Not saving it. Just never used it. I am comfortable with West Systems and know exactly how it works. I will read up on the Aeropoxy and see how to mix it and give it a try.
 

tbonerocketeer

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Micro balloons lower the density of the epoxy and (I think) makes it easier to sand - which would make it softer maybe. Not sure.

With that rocket you should be fine with the micro balloons. Some folks that's all they use. Unless you are saving the gold filled Aeropoxy for a super tough build, why not use it?. It is a structural epoxy after all. I've never used it myself though.
Micro ballons also makes the epoxy prone to cracking if you get to many, but it sands like balsa....colloidal silica is like sanding concrete
 

scsager

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Honestly - I would not use any filler at all. Straight epoxy will work fine.
 

MClark

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I use micro balloons for fillets, I add chopped fiber glass (small short ones) to defeat cracking.

M
 

mpitfield

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I have used the red baron flex cure epoxy mixed with micro balloons for external fillets with good success, on several builds. Lighter for sure but as others have stated it is prone to cracking, especially on larger radius fillets, so keep them small. I also use ES6209 pretty much exclusively for internal fillets and have on every size build. Overkill on most builds but if you have it, use it, as it has a shelf life and even using it as much as I have it is coming to the end of it's life and I still have a lot.

ES6209 is very easy to use, mix it up thoroughly @ a 1:1 ratio, apply it and let it cure 24 hours. I don't even measure it when mixing, I simply eyeball it as fillets are typically small batches.

https://www.rocketryforum.com/showthread.php?140664-MAC-BlackFly-build-thread&p=1702924#post1702924

https://www.rocketryforum.com/showthread.php?140664-MAC-BlackFly-build-thread&p=1702681#post1702681
 
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MikeyDSlagle

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Micro ballons also makes the epoxy prone to cracking if you get to many, but it sands like balsa....colloidal silica is like sanding concrete
Yep, you are right about that.



I use some sort of filler for all my fillets. Just makes more sense to me.
 

ECayemberg

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For mechanical properties alone, stick to colloidal silica. As Chris said, Microballoons make it super easy to sand, but greatly decrease tensile strength of the epoxy.

For what it's worth, if I'm filleting with West Systems, it's a mix of milled fiber for strength, and aerosil/cabosil/fumed silica for shapability.

Closing thought: if you're in a pinch, West filled with Microballoons WILL WORK. It'll stand up to the rigors of flight just fine, but you may find cracked fillets upon landing.
 

NateLowrie

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I use both. I use 25% the weight of the epoxy in microballoons and 5% the weight of the epoxy in fumed silica.

The silica is a thixotropic agent, meaning it will make the epoxy more viscous when it is not under movement but the epoxy will still flow like normal when you agitate it. It also imparts a marginal improvement in tensile strength. A lot different than the microballoons, which are strictly a filler and will decrease the tensile strength of the epoxy.

Use milled fiber if you need the strength. Otherwise microballoons make the mix easier to sand and that combo should be good for everything that is not high performance.
 

dr wogz

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I have used balsa dust in my fillets. comes out a bit rough, but sands OK.. I've heard of others using baby powder. again, sands OK, and smells 'pretty'!
 

MikeyDSlagle

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I have used baby powder. Can't remember the build I used it on though, Hurricane 38 maybe. US Composites sells talc as a filler.

I've gone to more task specific fillers. For my internals I will used chopped fiberglass because they are not going to be seen anyway. On the externals, depending on size of rocket and fillets and motors intended, I will lay down a root with the fumed silica. And cover that with either faring compound or Q-cells if necessary to make it easier to finish the visible part.
 

markkoelsch

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I am generally against microballoons and such. I am also against sanding structural fillets.

Use glass fibers, chopped carbon, or Kevlar pull mixed with epoxy for fillets. Then use an epoxy based filler over the top, and sand that smooth. That is my general approach.
 

boatgeek

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My go-to structural filler is wood flour, basically fine sawdust. It makes a thixotropic mixture (think creamy peanut butter, moves when you move it, stays put when you don't) like microballoons or colloidal silica, but is stronger than microballoons. It's not terrible to sand, either. Definitely wear a dust mask or respirator when working with colloidal silica--that stuff gets everywhere and it's not good to breather.

My usual procedure is to pull fillets with wood flour, then file/sand mostly smooth and cover over with a thin layer of microballoons, then sand to a nice finish for painting.
 

kjkcolorado

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I am generally against microballoons and such. I am also against sanding structural fillets.

Use glass fibers, chopped carbon, or Kevlar pull mixed with epoxy for fillets. Then use an epoxy based filler over the top, and sand that smooth. That is my general approach.
Mark, what is your 'epoxy based filler' of choice? Thanks.
 

Forever_Metal

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Not saving it. Just never used it. I am comfortable with West Systems and know exactly how it works. I will read up on the Aeropoxy and see how to mix it and give it a try.
Aeropoxy is all I use anymore... good stuff and lasts!

fm
 
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