Fiberglass?? Different resin/hardeners??

I just have a quick question which may just result a simple answer...or not.

In my search to locate a reliable method of applying fiberglass to a rocket, I wondered what the differences in the actual hardener and resins may be. (From what I do understand, the weave of glass measured in ounces is based on density and just that, weight or thickness.) I was at Home Depot the other day searching for their fiberglass solutions and came across the "Bondo" brand of hardeners and resins. I read over the labeling and the settling time is about 30-35 minutes. Granted, I would never use an automotive grade of fiberglass weave on a rocket, but what about the actual epoxy mix? What makes the hobby grade different from say, a commercial grade or automotive grade epoxy (hardener/resin)???

Thanks in advance....

PS - My initial use of the resin/hardener will be with the stretchable nylon material. I will get into actual glass weave later.

Keep in mind that I'm no expert on this.

My understanding is that the Bondo type resins are polyester based instead of epoxy based. I have been told that the polyester based resins are less suitable for our types of applications. One person who should know is Drake Damerau. He had volunteered to do some HPR strength of materials tests on RMR and has since published his results here. I haven't looked at the results much so I'm not sure that it covers the difference between epoxy based and polyester based resins but, it's a place to start and he may have a better answer than me.

The glue results don't even show up on there (which is weird--I know they used to be there. I do know that John Coker did some tests on different epoxies and had results on his page (no, I don't know the link), and actually had some VERY interesting results with epoxies, but I don't believe he touched on the polyester resins. I think I read somewhere that the issue with polyester resin has to do with heat resistance as opposed to strength.

If I recall correctly, the only epoxy that really made a difference for fillets was the thicker Aeropoxy. Bob Smith 30 minute and West (the thick version) came in at a virtual tie, which seemed odd to me, but hey...I didn't do any testing and I don't even HAVE West Systems yet.

Lets see, I'm not the biggest expert either, but that doesn't mean i won't give my 2 cents...

Mark is right about the bondo being polyester. I didn't think the strength of materials site tested polyester resins(?) I have always heard that these are not as good as regular epoxies for rocket apps. Any professional grade epoxy such as West, Aeorpoxy, and there are several others, is the best. I know this is especially true if you are using G10 fins and/or tubes. Polyester resins don't bond to this as well. That being said, I'm sure the polyester resin would probably be ok for many (if not most) applications...after all, you can use pantyhose and polyurethane Finally, the automotive grade cloth may be fine for a bottom layer, but you probably want a smoother outer layer. I have used it before for joint stiffening, but used an epoxy filler afterwards.

Mark,

I didn't even know there were different chemical compositions for the actual resins/hardeners. Ok, so that would make some sense. I could go with the theory that the polyester grade isn't heat tolerant.

I just wanted to make sure that this isn't one of those things like "rocketry shock cord" which in fact is just waistband elastic. Or, the good 'ol "shock cord mount" which is nothing more than a piece of paper cut to size. Of course, West Systems seems to be a boating repair type of fiberglass system, but has been proven to work great with rocketry.

Kermie,

What kind of epoxy (hardener/resin) are you currently using?

Thanks for the input guys. The natural progression of this hobby forces one to research and utilize higher grade materials and construction methods. Boy, this is leaps and bounds from wood glue and paper mounts.

Gotta love it though!

Polyester also doesnt have nearly as good adhesive properties. If you are building up a standalone fiberglass item, poly has some plusses... namely, much cheaper! But if you want your glass to also adhere to the tube... go epoxy.

Even in boatbuilding many builders are going to epoxy/fiberglass. Especially with boats that are cold molded, (a combination of laminated wood and fiberglass).

Polyester also outgasses some seriously noxious fumes when curing, iirc...

And no, I'm not an expert either!

-Nathan

Hey, do three non-experts = one expert? I suppose I'm about a third and expert in this field

Eugene,

Right now, what I'm using for glassing purposes is Zpoxy 20 minute finishing epoxy (don't let the 20 min. tag fool you...this stuff is very thin and takes a LONG time to set, not to mention cure). That's largely because I can't afford West for that kind of application at the moment (this will change with tax returns ).

One night in chat, BrianBarney mentioned that he had heard that the nylon isn't compatible with epoxy resins. I'm not sure of that either way as I haven't tried it. I used the Minwax Polycrylic with my nylon reinforcement.


Dick,

That being said, I'm sure the polyester resin would probably be ok for many (if not most) applications...after all, you can use pantyhose and polyurethane...

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You dissin' my pantyhose, babe? I'm told they look really good on my...errr...rocket.

Originally posted by KermieD
Eugene,

<SNIP>

One night in chat, BrianBarney mentioned that he had heard that the nylon isn't compatible with epoxy resins. I'm not sure of that either way as I haven't tried it. I used the Minwax Polycrylic with my nylon reinforcement.

Click to expand...

I was looking up some info on that Minwax Polycrylic and it doesn't seem to be a glue per se. It seems to be more of a lacquer, finish, or sealer as opposed to a hardening glue. The only reason I mention this is because the Polycrylic doesn't seem to add any strengthening properties to, let's say, an airframe. (Pure speculation of course. I've never used it before. I'm just guessing here. )

I'm sure after it dries it contains the nylon, but does it harden the tube or just coat/laminate the nylon and tube for a smooth flexible finish?

Originally posted by rstaff3
Hey, do three non-experts = one expert? I suppose I'm about a third and expert in this field

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"I'm not an expert, but I *did* stay in a Holiday Inn Express last night."



-Nathan

Eugene,

With fiberglassing or nyloning (), the real strength is added by the cloth, not the "glue". That's why they tell you to mop puddles or vacuum bag to squeeze out the excess resins. The Minwax polycrylic is sufficient for adding stiffness to the weave. It is a "protective finish" of sorts, but it does dry to a pretty stiff consistency. If you're using it, though, I would go with sanding the outer glassine or wax layer of a Kraft tube as opposed to peeling it. You'd be surprised at how much of the stiffness on Kraft tubes are attributable to that outer layer. I really don't know if there are issues with the epoxy resins or not, though, so try it once with West or with a finishing epoxy on a practice piece and let me know how that goes! I plan on glassing my next big bird, but might go back to the nylons for other projects.

I've been useing polyester resin on my RC airplanes for years with no problems at all with it not sticking to the surface. I've also used it rockety as well. There are two basic types of polyester resin out there, laminating resin and finishing resin. I would go to your local hobby shop and purchase some SIG finishing resin. Use the recomended amount of hardner. Once dried the surface must be sanded before anything else is applied such as glue, primer or another coat of resin. Finishing resin contains wax that comes to the surface allowing it to fully cure. This wax surface layer must be sanded off before you add anything else to the surface. I believe the Bondo brand resin is laminating resin which is great when layered build ups of glass such as making a real heavy repair or in making molded fiberglass parts. The big problem with laminating resin is in the fact it's almost impossible to sand since it gums up the paper. This type of resin does not contain wax and therefore a hard sandible surface is not present but it is instead more sticky to the touch. You can apply another layer of glass over the first layer without sanding. You could of course build up the layers of glass needed with the laminating resin and then finish it off with the last layer being applied with the finishing resin. Of course you can always use Epoxy Finsihing resin to apply the cloth. Yes there are two man types of Epoxy resin as well, with dozens of subtypes as well. Good Luck