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Gary Liming

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I have access to some West Systems 105/205. Which additive would I use to get it to approximate the peanut-butter consistency as well as structural properties of something Rocketpoxy for use in fillets, etc.? Something like their Microlight Fairing Filler 410 or their Colloidial Silica 406 or the solid 404?

Note: not looking to start a "which is best" thread, just trying to solve this problem.
 

prfesser

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Colloidal silica (Cab-o-Sil) thickens with the least *mass* of filler. It's extremely low-density, though, so a large volume is required.

My personal experience: it's easier to get a uniform mixture if one begins by adding epoxy to the filler, rather than the reverse. I always get lumps when adding filler to epoxy.
 

jd2cylman

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I use the 406 also. I mix the epoxy and add the 406 in. Just like prfesser says, it gets clumpy, so I beat the crap out of it mixing. I use the little 30mil cups. A full pump of 105/205 almost fills a cup. One cup of 406 to one cup of epoxy works perfect for me. I put them in a bigger tub to mix. The only problem with the 406 is that it's very poofy... stir carefully until it's wetted out. Maybe wear your mask. It's probably not good to inhale either... I got a pic here somewhere... Lemme find it. Here it is. Not perfect, but you can probably zoom a bit. Post 29,359.
 
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CPUTommy

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G_T

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It might be that you may try adding the filler in smaller batches rather than all at once. As the viscosity builds up, the shear force that can be applied to clumps increases, reducing or eliminating the clumps. I've never had a clump problem. YMMV?

Whenever I've used fillers - with certain unique exceptions - I've used too high a filler mass percentage for adding epoxy to the fillers to work. The exceptions - making a slightly thickened initial coat for tacking down light fabric in a complex mold, and making a glass fiber blob of chopped cloth scrap for stuffing into corners of molds.

If you are having a problem with a particular filler, it could be that using another manufacturer's filler will work better for you, you might have a moisture problem, or it might be that a blend of fillers will work better for you.

Adding milled fiberglass first for instance will increase the viscosity during the mixing process, helping to pull apart clumps. IMHO it won't improve strength appreciably, but it may aid in the mixing process.

Most times I used a combination of fillers. 410 + milled fiberglass for lightweight peanutbutter filler, for instance. The volume of stuff which goes into the epoxy is way more than the initial volume of the epoxy. It's like the Donkey on one of the Shrek movies - Are we done yet?

If a filler is just to create a volume solid than it is ok to whip air into it (just don't make a dust cloud as that is uniformly BAD for you), so don't do the whipping until it is blended. But if a filler is to be structural, air is the enemy. So then you have to mix much more carefully, or possibly even consider degassing methods.

Fillers tend to increase the volume of the epoxy and to reduce its thermal conductivity. Epoxy is generally exothermic - some rather more so than others. Epoxy with fillers can cook itself off quite a bit faster than epoxy without fillers. Expect your working time to be reduced a lot, possibly by half even. You can reduce this of course by spreading the mix out in a thin layer on a plastic plate, a playing card, aluminum foil, etc, after or even during mixing depending on quantity required.

I've never done it, so I can't comment on it, but some people have mixed fillers with the component epoxy parts before mixing them together. That way at least you can mix for as long as necessary without concern for kicking off and killing your working time. But you have to be very careful of epoxy mass loss to mixing items messing up your ratio. It is probably better suited to larger quantities rather than small batches.

Epoxy with fillers can easily kick off hot enough to smoke, to melt plastic, or to burn you. You have to be careful once the batch size is no longer small.

Some less common fillers may be worth considering on occasion. Powdered aluminum in sufficient quantity makes a decent poor-man's tooling coat for a mold. It also increases the thermal conductivity so the center of the mix doesn't get quite as hot as fast, extending the working time a little compared to most other fillers.

Sorry, I typed much more than I had intended!

Gerald
 

dr wogz

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I'm a fan of their 407 fairing filler. stand-up thick, and easy to sand afterwards..

While fillets add strength, they are not the structural part of a fin.. (or at least they shouldn't be!)
 

mtnmanak

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For fillets, I use either the 406 Colloidal filler or the 404 High Density filler. The 404 is very dense. It is great for structural bonds. If weight is an issue, I stick with 406. If high strength is desired over weight concerns, I use 404.

The biggest issue I have with West Systems fillers is that I couldn't find smaller containers of them to buy. Maybe I just looked in the wrong places, but the 7" high containers were the smallest I could find. I have a number of the different fillers in those sizes and will probably never run out of them. On the other hand, I pretty much will never have to spend any more money on fillers. These will last me for at least a decade at the rate I am using them.
 

jd2cylman

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I’ve used my first can of 406, and am a third into the second... There’s so much floof with the 406 that a decent size container still is mostly container weight...
 

mtnmanak

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I’ve used my first can of 406, and am a third into the second... There’s so much floof with the 406 that a decent size container still is mostly container weight...
Nice! Gives me hope that I didn't buy this seemingly huge amount in vain!
 

G_T

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You want something that feels like like an empty container, try the 410. Phenolic microballoons. Mixes extremely nicely. If you use it, you'll find you need to use way more than you think you do.

I've never seen West brand fillers in smaller containers. But at least you don't run out often.

About quantity, the Kevlar flox I picked up for abative insulator testing was a cubic foot. Some things you just can't get in really small quantities. My cotton flox supply came from a friend's cubic foot... I may have used all of that up. I don't recall. It's much more dangerous to mess with than you'd think at first glance. Ref - Brown lung.

Cotton flox is really nice for thread reinforcing as it is not brittle and wets out fairly well. Wax bolt thread, put in cotton flox loaded epoxy into rough clean oversized threaded hole, stick in waxed bolt, wait for cure. Break bolt free. Nice threads. Sort of how one could also use JBWeld (IIRC, you can make something somewhat similar with powdered iron plus calcium carbonate, but needs near room temperature cure high heat tolerant epoxy). To get closer to the commercial one -> https://www.wired.com/2016/08/whats-inside-industrial-epoxy-bpa-somethin-garlicky/ Easier to just buy the commercial stuff.

Gerald
 

blackjack2564

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406 actually gives strength to epoxy...used in yachting to re-inforce cleat attachment to decking. one of few additives that does. for my money the best one to use...oh by the way...that huge container....only holds 1.9 oz by weight....lol
 

Gary Liming

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Just a follow-up: I tried the 406, mixing like the professor said, and it mixed well, no lumps, and it stayed put on the treated surface, just like I wanted. Thanks to all for the advice.
 
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