Epoxy and Finishing Resin: What is the difference? - RC Groups
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Jun 29, 2010, 04:31 PM
Micro Boat Forum Founder
boredom.is.me's Avatar

Epoxy and Finishing Resin: What is the difference?

Say you are making small boat hulls that do not require a million layers of fiberglass. Is epoxy what you want, or would you want finishing resin? What is the difference between finishing resin and epoxy?

Also in the case of really small stuff (6" range), would CA be able to perform as well as epoxy?

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Jun 29, 2010, 04:51 PM
Just fly it!
wyowindworks's Avatar
You would want a laminating resin. There are 3 types of laminating resins that are typically used for structural components: epoxy, vinyl ester, and polyester. Epoxy performs the best but is also the most expensive. Polyester is the cheapest, stinks like made, and has the poorest performance of the 3.

There are typically two types of epoxy: bonding resins (like 5 minute epoxy) and laminating epoxies. You would want a laminating epoxy.

Finishing resin is typically used as a sealer to prep a surface for painting or for fuel proofing. Some model companies (Great Planes, Pacer, Sig) say that their finishing resin is good for making fiberglass parts, some say that their finishing resin should NOT be used to make fiberglass parts. In the end I think it's best use a resin specifically designed for making composite parts like: MGS, West Systems, US Composites, EZ-Lam, Resin Research, Adtech...to name a few.

CA would not be able to perform as well as a laminating epoxy.

Last edited by wyowindworks; Jun 29, 2010 at 05:05 PM.
Jun 30, 2010, 01:06 AM
Wood Chucker
Lacquerhead's Avatar
So what properties of laminating resin make it the right tool for the job? The finishing resin I have flows much, much better than the bonding epoxy even when it's thinned out. I'm assuming it is more than just how it flows but I am afraid I just don't know what nor why. I'm looking to further my composites knowledge as well.
Jun 30, 2010, 01:26 AM
Just fly it!
wyowindworks's Avatar
I'm sure the finishing resin does flow out much better. Thinning bonding resin with a solvent should only be done in the most desperate of situations....so much so that I would never do it.

Honestly, I've never used a "finishing resin". I don't really know it's properties as the properties of "finishing resins" are rarely published so I keep my distance.

In the boating and surfboard industry a finishing resin contains wax to create a seal so the resin fully hardens and isn't tacky. A laminating resin contains no wax so following application of resins will bond better. This generally only applies to polyester based products. Epoxy resins don't need to be "sealed" to eliminate the tackiness. So why the hobby companies are calling epoxy based resins a finishing resin dumbfounds me. In molding applications, the polyester resin is "sealed" by the mold surface and typically doesn't need wax to eliminate tackiness.

As a rule of thumb I avoid buying resins from hobby stores. The hobby store brands get their resin from some unpublished company with unpublished specs. Ask the store clerk what's the Flexural Modulus using the ASTM D-790 test method. He won't have a clue....and neither will Great Planes, Pacer, ect.

I recommend using a resin made by a company that makes resins and tests the properties of their resin....or at least knows them.

Last edited by wyowindworks; Jun 30, 2010 at 01:50 AM.
Jun 30, 2010, 09:00 AM
Micro Boat Forum Founder
boredom.is.me's Avatar
Nice info from the both of you.

I was interestes in Z-Poxy. http://www.gravesrc.com/PACER_Z_POXY..._p/paapt39.htm
it contains epoxy resin and polyamide resin. Not that my application would be for an extremely small boat.

Jun 30, 2010, 09:55 AM
I DS slower than I build!
Cory's Avatar
I don't think the one you linked to is what you would want to use. This one could be used. http://www.gravesrc.com/PACER_Z_POXY..._p/paapt40.htm

I used Z-Poxy finishing resin on one fiberglass project. It's OK, but not as good as the true laminating resins that Adam mentioned. West Systems is much easier to work with and produces a superior part. I don't have personal experience with the other brands, but there are many others swear by them. If you're in a rush, have the Z-Poxy at hand, don't have quick access to a real laminating resin and don't care to have a top quality part, go ahead and use it. If any one of those don't apply, use a good finishing resin.
Last edited by Cory; Jun 30, 2010 at 10:30 AM. Reason: stupid 1st grade grammar error
Jun 30, 2010, 10:27 AM
Micro Boat Forum Founder
boredom.is.me's Avatar
Looking at this chart from West Systems, 105 and 209 would be good.

Jun 30, 2010, 02:11 PM
Registered User

West systems

I have used alot of West systems for laminating, wood boat construction and finishing. When I use it for finishing, i prefer the fast hardener and I thin the mixed resin about 25% with an epoxy paint thinner. Yah, I know it's supposed to diminish the great properties of epoxies, but the benefit is a slightly more rubbery resin so (I'M hoping) for less stress cracks at the joints. Some people don't thin but brush on a coat leave it set for 10 minutes and wipe as much as possible off, then heat it with a heat gun to get it to really penetrate. Most model boaters are looking at two coats to completely seal (some use three) hardwood ply. I then usually go to a couple coats of Klass Kote color. I don't use primer anymore, I prefer to use a color coat as primer (for durability). I do lightly sand the epoxy finishing coats between coats to flatten, knock off nibs and runs. I try to catch any big boo-boos before the second coat of epoxy and use a epoxy/microballoon filler putty to patch. During this phase of construction, hot weather is your friend. Slow hardener in this case is just tooooooooo slow. I like to be able to least get a step done a day, with things hardening overnight. Used to like Hobbypoxy Formula 2 but it's been out of production for decades. Rudy
Jun 30, 2010, 03:12 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
I wasn't understanding the chart earlier. At first I thought that some of the hardeners worked better with different additives, but now I see that they all work together.

So when applying glass, is it best to lay and let one (1) layer dry completely, or should you should lay them all at once?
Jun 30, 2010, 03:29 PM
Just fly it!
wyowindworks's Avatar
Is the glass being laid-up in a mold or being used to reinforce a wood hull?

Jun 30, 2010, 03:59 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
It would be a mold if I decide to actually do it.
Jun 30, 2010, 04:23 PM
Just fly it!
wyowindworks's Avatar
You would do all the layers, one after another, while the resin is still wet. This will give you the best inter-laminar bond.
Jun 30, 2010, 04:41 PM
Micro Boat Forum Founder
boredom.is.me's Avatar
And what would you have to do to prep a wooden mold? I am not completely sure about what I have seen/read/heard. You would varnish the wood after you get the desired shape, then apply a release agent to the mold surface... right?
Jun 30, 2010, 04:51 PM
Registered User
talonxracer's Avatar
I use the West 105/205 for laminating.
I use the 105/205 with 403 filler for wood construction, 404 filler for engine mounts and high stress areas, 408 for low stress fillets

For waterproofing I use the 105/207, the 207 special coatings hardner is great for waterproofing as it is alot thinner and responds very well to a little heat. I apply the 105/207 with a close cell foam roller very thinly, hit it with a little heat from a heat gun and you can watch it soak in. Wait for it to green up and then apply another thin coat with another closed cell foam roller. I also use the 105/207 for laminating small non load bearing stuff.
Jul 01, 2010, 03:05 PM
Rangers Lead the Way
Used West (and did glassing) for the first time two weeks ago. Small jobs. My observation is that the 105/205 pot time seems pretty short. The stuff gets to taffy real quick. My concern is that if I were doing a large surface, say glassing a wing, that (1) the 105/205 would not penetrate very well and (2) would set pretty fast.

I also experimented with thin CA dripped onto glass cloth over wood. Unlike the epoxy, it's capillary action (1) pulled the cloth down against the wood and (2) penetrated the wood, hardening it.

What can I do to get the West to do this? Basically I need it to be more like water in consistency and to be slower. Also, is there anything wrong with using CA to tack the cloth before I do my squeegied epoxy layer?.

Any help is appreciated as I am a total newbie here. I am very excited about the structures I can build with this and working with 105/205 and the pumps could not be easier. What a great product.

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