Epoxy Amendments

[Mad Rocketeer]

I've got a question about epoxy amendments. First some background, then the question. Please correct any misconceptions in the background stuff as well.


Background:

When glassing tubes (or Kevlar or carbon), the proper technique is to get the fiber and the tube wet with the epoxy then squeegee (or vacuum) out all the rest that one can. Then, lightweight epoxy-compatible fillers can be rubbed into the weave and over the top, to be sanded smooth. The idea is that more epoxy than this doesn't contribute to the strength, but only to weight. Sanding into the fiber matrix weakens the structure.

Adding milled fiber (tiny fiberglass filaments) to epoxy adds strength and hardness but also weight. Milled fiber can be added up to about 1:1 with the resin (not including the hardener). Adding Kevlar pulp to epoxy adds strength and impact resistance. Adding chopped carbon fibers to epoxy adds strength and stiffness. Chopped carbon fibers and Kevlar pulp are added at about 1:16 fiber to resin. Carbon will be lighter than the epoxy, and Kevlar may be too. Adding microballoons to epoxy reduces density and therefore the weight of the mix. Microballoons weaken the mix though, since they are hollow and largely air. Microballoons can be added up to about 3:1 balloons to resin.


Question:

What happens if one adds both reinforcing amendments (such as milled fiber, Kevlar pulp, or chopped carbon fiber) and microballoons, mixing the reinforcement in thoroughly first, then the microballoons? Will it end up strong and light, like a properly glassed tube (see above), or will the microballoons interfere with the proper matrix of fiber and resin?

Would it be better to go with layers like this (using fillets as an example)?
[Each new layer is added when the previous one is ready to handle but not fully cured.]
1.) Paint the tube and fin root area with a thin layer of straight epoxy for better penetration.
2.) Mix epoxy and reinforcement, and make a thin strong fillet.
3.) Mix epoxy and microballoons (or use some other prepared light epoxy-compatible filler) to finish the basic shape and size of the fillet. Smooth it.
4.) Paint over the filler with a thin layer of finishing epoxy, spray on a little 91% rubbing alcohol, and create the final glassy smooth surface.

Can steps (3.) and (4.) be combined?

Anything I'm missing?

Of course, I'd use gloves for all epoxy work and take precautions against inhaling fibers or microballoons.

Thanks.

 

[Stymye]

sounds good to me because I don't think it would make sense as you mentioned, to mix microballoons with fibers.(weakener with a strengthener)

one question,after you have smooth sanded the microballoon layer why would you pour more epoxy on it?

it seems that would defeat the purpose of the sanding and smoothing part by adding a hard to sand layer on top of it.

I just finished some fillets on my MSH v2 doing just what you described(except I didn't add any fibers to the first layer)
I also followed with a microballoon layer than I just applied a skim coat of filler to fill any scratches or pinholes.

since I let it fully cure between layers I made sure to clean off the amine blush with alcohol than sanded between the layers also.

 

[Stymye]

sorry MR , I wanted to add a pic to my reply but I couldn't after I posted

heres the fillets after a little sanding and priming, microballons are great stuff!

 

[Mad Rocketeer]

Andy:

Sweet! Those fillets look perfect, from what I can see.

Andy asks: One question, after you have smooth sanded the microballoon layer why would you pour more epoxy on it?

It seems that would defeat the purpose of the sanding and smoothing part by adding a hard to sand layer on top of it.

My thinking went something like this.
* I've seen techniques posted for making glassy-smooth fillets by using straight epoxy with the surface thinned with a bit of alcohol applied to the surface or to a gloved finger/spoon/popsicle stick and smoothed/shaped and left to flow/level itself into perfection.
* I wasn't sure that epoxy thickened with microballoons would smooth/level itself this way, thus leaving it only as smooth and well-shaped as sandpaper (or my gloved finger) can get it.
* I wanted the strength of a toughened fillet underneath, the lightness of a low-density material to shape and size the fillet, and the smoothness that flowing epoxy can achieve but my inexpert sanding cannot.
* I figured that I could smooth the microballoon layer fairly well, thus providing a good base for the smoother flowed-on layer.
* If I got the final layer right, I wouldn't want or need to sand it.
* A harder layer on top might prevent some dings and hairline cracks in the fillets.


Steve

 

[Stymye]

your right, the microballoon mix will not flow much, you have to tape off the fillets, spread it ,shape it ect...(I get a very smooth fillet with a spoon) once sanded it leaves a nice smooth surface for paint
I asked because an untouched layer of epoxy will not hold paint very well so you would have to sand it anyway. the glass look comes from priming and wet sanding not directly from the epoxy surface finish...but it's nice to start with somthing smooth like your describing.

 

[Mad Rocketeer]

Ahh! I hadn't considered that epoxy doesn't take paint well untouched. I was thinking I could just prime and paint over a glassy surface, but you're right. I'd have to rough it up anyway. I guess there would still be an advantage in giving it a hard crust, though, for durability.

Would adding reinforcement to the crust epoxy help the paint to stick? I.e., would the paint stick better if the epoxy had little fibers perhaps poking out on the microscopic level?

Is microballooned epoxy porous to any degree? Would dripping water-thin CA over the surface harden it any? Seal it any? Mess up the paint adherance? If it would be effective, it would be lighter than an epoxy skin.

Does microballooned epoxy really need a hard shell to be durable enough? What ratio of balloons do you use?

 

[DynaSoar]

Epoxy doesn't paint well?

Mine does. It gets no treatment between curing and primer, unless it happens to get lacquer sanding sealer. They all look fine. Maybe it's the Devcon 5 minute?

 

[Daedalus]

Originally posted by Mad Rocketeer
I guess there would still be an advantage in giving it a hard crust, though, for durability.

The epoxy layer will just be heavy and weak. Little point in doing it if the filler layer is done propperly. If it isn't smooth re-fill with epoxy filler or as part of the paint system.

Originally posted by Mad Rocketeer
Is microballooned epoxy porous to any degree? Would dripping water-thin CA over the surface harden it any? Seal it any? Mess up the paint adherance? If it would be effective, it would be lighter than an epoxy skin.

Does microballooned epoxy really need a hard shell to be durable enough? What ratio of balloons do you use?

Hadn't noticed it being porous and it is sufficiently hard by itself. I have never had problems with areas using microballoons being weak or soft. They sand very easily and to a very good finish. With a decent epoxy it sets hard and sands easily - fillets made of 5 min epoxy are very hard to sand as the epoxy doesn't set really hard and tends to gum up the sandpaper.

I find for fillets taping either side of the fillet and then pretty much spooning the filled epoxy on - it doesn't flow that much - certainly not pourable. I then smooth it with a tongue depressor or similar to make the fillet, it then doesn't need much sanding at all.

I never measure microballoon ratios just add it until it feels right for the job. Mix the resin and hardner then when fully mixed add the microballoons to the consistency you want - I like to be able to pull a peak on the mix with the stirrer that slowly slumps back - probably in the 2 - 4:1 ratio range so 3:1 is probably about right.

 

[DumasBro2]

Mad-
What you will and are finding out is there is as many techniques as the people who use them. Sort through and use what you like and modify them accordingly. What works well for one person may not for you. That being said here's my 2 cents. I use West Systems Epoxy for building and laminating, for me it's cheaper and I like the product. For structural work, like centering rings, I'll add milled glass to the epoxy. For just filling I'll add fairing filler, this sands great. If I want it easier to sand with some strength I'll use both. No certain ratios, I just add until I get the consistency I want. For glassing I will wet the tube/fin with epoxy and lay the glass on dry then work it out with a spreader. If I use a heavier weave cloth I will finish with a layer of 2 oz. cloth for a "sanding vail". I really like to use 3.4 HS satin weave cloth as this can pretty much be sanded to remove the blush and then filled with a high solids primer.

steve

 

[Mad Rocketeer]

Good feedback.

I welcome differing ideas when working on my own thoughts. We're like blind men exmining an elephant. When I walk up, if all the blind men spent their time examining and reporting on the nature of the tusks, I'd never learn about the ears. I.e., it's in hearing different ideas, and their interplay, that I learn the most. Good researchers here, and good teachers.

 

[Stymye]

Originally posted by DynaSoar
Epoxy doesn't paint well?

Mine does. It gets no treatment between curing and primer, unless it happens to get lacquer sanding sealer. They all look fine. Maybe it's the Devcon 5 minute?

Dynasaur ,you can paint directly over the untouched epoxy and it will look fine ,but after a flight or 2 you may notice some hairline cracking along the fillet from normal stress
because the paint has very little to bond to on such a hard smooth surface ,I'm not sure about Devcon compared to others but most epoxys will blush once cured resulting in an oily feel to the surface (amine blush)
so I always wipe the surface with alcohol to remove it than scuff the surface to help the primer bond better.I've noticed less cracking along the fillet ,since I've started prepping the surface that way.

It's just one of those little steps I've found, that make a small difference down the road.

 

[Missileman]

I mix microballoons and epoxy to about the consistancy of catsup.
This seems about right to get a good smooth spreadable mixture but solid enough to be able to do all of my fillets at the same time without worries about them running.
I smooth out and shape fillets with a popsicle stick for smaller birds and the back side of a plastic spoon for the bigger projects.
EDIT: word of caution, use a fairly long cure epoxy (I use west systems with 45 min cure hardner) when mixing with fillers. For some reason epoxy seems to cure a bit faster when mixed with fillers.

 

[Mad Rocketeer]

I was planning to do my LOC Graduator with Bob Smith 30-minute epoxy throughout. Is that slow enough? My thought was to do the butt joints with straight epoxy, so it will soak in well on both surfaces and can be done nice and thin. Then for fillets, to paint the area that will be under the fillet with the same thin film of un-amended epoxy, then add a small fillet of strengthened (e.g. milled fiber, Kevlar pulp, etc.) epoxy over that for both inside and outside fillets. Then for outside fillets, go over the hard fillet with a epoxy + balloons fillet to get the correct size and curve for aerodynamics and a pretty smooth surface. Finally, another layer of un-ameded epoxy over the top of the balloon mix to get a glass smooth surface. My idea was to do this in stages, letting each layer get at least thick and maybe hardened before adding the next layer, but doing each new layer before the previous one has the chance to fully cure. I understand that will allow the layers to bond to one another with a strong chemical bond rather than just a physical one. I.e., it would be like one continuous layer of epoxy, with the amendments changing within it with depth. It sounds like a lot of epoxy, but I'd want the layers to each be rather thin and add up to a normally-sized fillet. The balloon mix should be the thickest part, to save weight. It may be (and this is where the discussion of painting over epoxy came it) that the glassy surface I envisioned as the outer layer (thin with alcohol and allow to flow to its own level to be smoother than I could so with a spoon) would be too smooth to paint well, making the last layer unnecessary. Another consideration would be whether the top layer would make the fillet more durable due to a harder surface. Sounds like that may be unnecessary. All thoughts are welcome.

 

[Missileman]

30 min is fine as long as it is not that hobby store 50/50 mix stuff.
I tried that with a microballoon mix and was left with some nasty unfinishable fillets.
I believe the top layer you described is not needed.
You underestimate how smooth the microballoon finish is even after some sanding.

 

[DumasBro2]

Mad-
I have used Bob Smith's 30 min. epoxy and like it however, if you will be doing any glassing or using a lot of epoxy West Systems is much cheaper in the long run. Bob Smith epoxy is thicker than West Systems so it doesn't need as much filler. I have used it alone for fillets and works fine. I have also used it with fairing filler and milled glass however it gets thick pretty quick and won't flow as well. I have never used it with microbaboons.

-steve

 

[Mad Rocketeer]

Hmmm. Bob Smith is 50:50, but it's not the Wally-World stuff. I got it at a hobby store. Will it turn to goo with microballoons then? I can get West Systems, but it would take me forever to use up a quart of the stuff. Is there a way to get West Systems or Aeropoxy, etc., in small-time quantities? Seems like I've heard of sample packs somewhere. Is that the only way? Sounds like I should practice on scrap to be sure in any case.

 

[Stymye]

system 3 has a sampler kit for an excellent price considering all the components you get with it and it goes a long way(unless your fiberglasing a huge rocket). I would highly recommend it to any one wanting to try out the system type epoxys, and to get a feel for the different additives

https://www.ndic.com/systemthree/trial_kits.asp

 

[Missileman]

Originally posted by Mad Rocketeer
Hmmm. Bob Smith is 50:50, but it's not the Wally-World stuff. I got it at a hobby store. Will it turn to goo with microballoons then? I can get West Systems, but it would take me forever to use up a quart of the stuff. Is there a way to get West Systems or Aeropoxy, etc., in small-time quantities? Seems like I've heard of sample packs somewhere. Is that the only way? Sounds like I should practice on scrap to be sure in any case.

I said the same thing when I bought a quart of of West System back in late spring. I started on my second quart a couple of weeks ago
At any rate. The thickness of the epoxy is key.
I have had success with 50/50 mix.20min finishing epoxy. It is much thinner and mixed well with the fillers.

 

[Mad Rocketeer]

I'm a real epoxy newbie. I've used a little of the Wally-World stuff for home repairs,etc., but none so far for any hobby use, like rockets. My new LOC Graduator will be my first epoxied rocket.

Seems to my inexperienced mind that the issue with Bob Smith and microballoons (or other amendments) may be the ratio of resin to amendment/fillers. The 5:1, etc., systems have mostly resin in their mixed epoxy. The 1:1 stuff like Bob Smith will have a lot of filler in the mixed epoxy, so two effects will be in play when adding the balloons. (1.) The balloon to resin ratio will be based on only 1/2 of the liquid, making the proportion of amendments with respect to resin considerably higher for any given balloon to liquid ratio. (2.) The mixed epoxy already has a lot of filler in it, adding to the total of "added stuff" in the mix. Could that be why missileman got nasty fillets with 1:1 epoxy and microballoons? I.e., maybe the 1:1 stuff just can't accept as large a portion of balloons and still function correctly. If so, that would limit the lightening that could be done with balloons with 1:1 epoxies.

What would be a good ratio of balloons to use with Bob Smith 30-minute? is there an acceptable/workable level?

Missileman: How many rockets did it take you to use up a quart of West Systems epoxy? Does one need the pumps, etc., or can one just measure it with graduated cups, syringes, or whatever?

 

[Stymye]

generally, phenolic microballoons are mixed 3 parts MB to 1 part premixed epoxy,,give or take
or somewhere in the thick milkshake to peanut butter range

microballoons alone are added to make the epoxy more sandable
and will thicken the mix as well

thickeners are simply for that- thickening, but does not make it any more sandable

mixing the two makes no sense...if you want thick add a thickener and it won't degrade the strength like microballoons will, if you want sandability add microballoons

someone who adds a pinch of this with a dash of that ect
simply has money to burn

I understand adding a strengthener (chopped fibers) with a thickener is common and makes sense.

doing it in layers is probably the best way rather than mixing everything together in one batch

 

[Missileman]

Originally posted by Mad Rocketeer

Missileman: How many rockets did it take you to use up a quart of West Systems epoxy? Does one need the pumps, etc., or can one just measure it with graduated cups, syringes, or whatever?

About 6 or 7 but 2 of them I fiberglassed the airframes (that sucked up alot of epoxy)
Yes you can measure and not use the pumps.
I wasted quite a bit with the pumps by mixing too much.
All told though, it is still cheaper by the quart and unmixed will last forever.

 

[Mad Rocketeer]

I went and looked at the West Marine store again and saw West Systems resin for $26/quart, hardener for ~$15/quart, and mini-pumps for ~$15 per set. Hardeners/fillers/thickeners aren't cheap either, on an up-front basis. I can see that they would save money over the long haul for someone using a lot of epoxy though. Are these typical prices? Is there a better way?

 

[DumasBro2]

Prices are about right. You can pick them up for 10% less at: https://www.mrfiberglass.com/west_system_products.html .
The fillers will last you a long time. It does seem like a lot up front money. I just picked up a little here and a little there. Still, cheaper in the long you if you can afford the upfront costs. Always nice to have the stuff around.

steve

 

[Stymye]

scroll back a few threads look into the system 3 trial kit , the price even includes shipping. you don't need the pumps unless your glassing tubes , it despenses way too much epoxy for glueing purposes. I put the 2 components into plastic bottles like the hobby stuff and squeeze out what I need . you can do it on a scale , count the drops , or use small mixing cups.

the trial kit will last a suprisingly long time if your not glassing bigger rockets.and has all the amendments included, you won't find a better deal to start out with.

 

[Missileman]

Originally posted by Mad Rocketeer
I went and looked at the West Marine store again and saw West Systems resin for $26/quart, hardener for ~$15/quart, and mini-pumps for ~$15 per set. Hardeners/fillers/thickeners aren't cheap either, on an up-front basis. I can see that they would save money over the long haul for someone using a lot of epoxy though. Are these typical prices? Is there a better way?

Commonwealth Displays has West System for:
Epoxy $20.72
Hardener $10
Pumps $9
I imagine if you look around you will find it even cheaper.
Marine supply stores are notorious for high prices.
I have looked at the System3 trial kit and at first glance it looks like a great deal. After a bit of math. You get a total of 15 oz. of mixed epoxy of various types for $20 the rest of the kit is mixing cups, stir sticks, gloves, ect... (I get my periphials at the dollar store in quantity)
That being said for about $40 with west sytems you get 39 oz. mixed epoxy, that is including the pumps that are reusable so the long term cost is actually even lower.

 

[DumasBro2]

If you have kids or know someone that does, Popsicle and corndog sticks work well to mix with, and lets not forget the Dole fruit cups………

steve

 

[OARJeepr]

I mainly use the west system. I have the pumps but most of the time I just waste a lot if I use them to dispense resin and hardener. Instead I use old 3ml density syringes that I get from work. Sometimes it's nice to work in a lab. This stuff is expensive but once you figure it all out its a lot cheaper than buying epoxy by the tube.

I usually mix the epoxy and fillers and then let it sit for 10-20 minutes. The consitency evens out and its much easier to work with then.

It's really not worth it save popsicle sticks when you can buy 1000 of them from hobby lobby for $1.50 or so.

 

[DumasBro2]

Guess I just don't like throwing away something I can use regardless of the price.

steve

 

[Mad Rocketeer]

Sticks and cups, I have. Ditto a few disposable gloves and brushes. These I bought cheap. I also have a lot of plastic spoons, accumulated from visits to fast food places.

If I go the West Systems route at some point, I'll probably go ahead and get the mini-pumps, since they can be had for under $10. I probably won't have many jobs for which a whole pump at a time is appropriate or effecient, but they'd be a convenient way to dispense resin and hardener into small graduated cups, syringes, and the like, especially as the material gets used and is farther from the top of the can.

I picked up the West Systems booklet when I was at West Marine. It has a lot of good information in it, most or all of which I'd already learned here. Cool!

The System 3 sampler looks like a good way to try out a lot of stuff for a small price before investing in larger quantities of anything.

I don't see myself needing to glass any airframes soon. I think my rocketery uses will be more on the order of my new LOC Graduator or maybe glassing on some narrow fiberglass reinforcement in fin-tube joints, etc.

Good advice on shopping the web for epoxy when the time comes to get more & better stuff.

 

[edwardw]

I have the pump system from West Systems and when I don't feel like using a whole pump I measure it by weight. 10 gram batches are a good size. I'm using the rest of my West Systems and will be switching to Aeropoxy soon because I liked it when I got to work on a project with it.

Edward