Epoxy vs Polyester, is it Euro vs US?

[JCAustralia]

Hi

Most of the european companies use epoxy resin fibreglass for their hulls and claim that they are superior than polyester (for example MHZUSA website).

On the other hand it seems that the US companies use polyester resin fibreglass for their hulls. I am also in gas boats and its the same story....

In Australia we tend to follow the americans.....

Why is that the case? Is it a cultural thing? Is epoxy really superior than polyester?

If that's the case why would the american companies not use epoxy resin fibreglass, or at least as an option on their premium boats? There would be a market for it if epoxy is better than polyester.... Or is is just a matter of keeping cost down? If I'm spending $$$$ on a boat and upgrades I would not mind paying a little extra if its made with epoxy, ......


Would love to hear about your opinions......

Cheers

JC

[Gerwin Brommer]

Yep, the cost plays a major role in it.

[Jeff Wohlt]

Most American boat builders/plants have been set up with tools long ago for poly/glass. All your guns and choppers, etc were built around poly. It is cheap, easy compared to epoxy. Certainly epoxy is far better in quality and durability.

[Cat-Boi]

No contest, epoxy is superior.

[NORMKRIS]

Epoxy

Epoxy is the way to go!

[yurkanip]

Polyester resins and catalyst...are cheaper than epoxy and hardener. Poly is also stiffer/more brittle than epoxy.

Epoxy is much stronger, can handle some flex and saturates different glass/fabric weaves easier. Thus, making it easier to use less resin and get the same if not more strength vs using polyester resins. BUT with my experience in plug and mold making for hulls, polyester resin only binds to tooling gel. Epoxy should not be used to make a mold if tooling gel is used.

this is from my experience, with both resins while building hulls.

[AndyKunz]

Polyester is just TOO SMELLY! I've used epoxy exclusively for years and expect to never change.

Andy

PS - I'm an American. Guess it's not a Euro/US thing.

[raptor347]

I've been building composite parts for many years (long before I started building hulls). I've always used epoxy because it makes a better part if it's done right. Building with epoxy takes more effort and slightly different mold design.

Most US hull bulders use poly for several reasons:
1. Cheaper
2. Faster
3. Works with cheap fiber mat

I make my molds with epoxy as well. There are epoxy specific tooling surface "gel" coats as well as epoxy specific tooling mat. Again, it goes back to the above reasons as to why people use poly.

[befu]

differences:

Repost of some information I posted earlier in different thread.

New information pertaining to post here:

Polyester is cheaper and easier to work with. Bonds to gelcoat very easily. You can also use glass mat which makes layups even cheaper.

Never noticed a difference in wet out due to resin type. resin quality - absolutely! You can get a wide range of laminating resins in epoxy or polyester that will wet out differently.

Strength: Epoxy is slightly stronger than polyester resin, by about 10%. But most of the strength comes from the composite. Epoxy allows you to use carbon fiber.

Epoxy is more expensive and mixing ratios are critical between resin and hardener. Polyester does not use a hardener, it uses a catalyst so it can be varied.

Polyester stinks!!!! If this is an issue, Epoxy is your only choice.

Both work, epoxy is better. The real question is how much better?

Old information if you wish to bore yourself and read:

http://forums.offshoreelectrics.com/...lyester+kevlar

Cloth to resin. This is another sore point with many people, how much resin they use. A composite is just that, made up of more than one thing. If you use carbon and epoxy, the resulting strength is a combination of both materials.

First a note on resins:
Now you hear people talk about how much better epoxy is than polyester. Made from real glass, not polyester. Well, neither is glass, they are both resins. Glass is a form of reinforcement. Polyester is usually in the low 9,000 psi tensile strength (TS) range. If I remember, it is 9200 to 9300, depending on quality, where epoxy is 9,800-10,000 psi TS? Epoxy is only about 10% stronger. Not bad and it is great stuff, but it is not like polyester is garbage! Epoxy does allow you to use carbon cloth as it is compatible with the binders in the cloth, this is the big payoff.
I am not sure if it is all epoxies though. Does anyone know the answer to this? Your laminating resins are formulated to work with the binder in the reinforcement. I have no idea if the cheaper epoxies sold under hobby use will work with the binder. Sure, it will set up and get hard, but it is not properly bonded together. This is complicated chemistry that I do not understand, that is for the manufacturers to know. Glass mats should never be used with epoxy, incompatible binders.

Composites:
Let’s say you are using carbon which is 170,000 psi TS. And you lay it up with epoxy which is 9,800 psi TS. People see that 170,000 and go WOW!
Carbon layups should be about 40% resin to 60% carbon by weight. Let’s go a little heavy on the resin and use 50/50. 9800 for epoxy, and 170,000 for carbon gets you a composite strength of 90,000 psi TS. (you have ½ epoxy, ½ carbon) Ever see those layups people do? Nice and shiny, like the resin was smoothed over the carbon! I would say people are using 3 to 5 times the epoxy to the carbon, which puts your strength down to 50,000 to 36,000 psi TS. Hmm, where did that sexy 170,000 go?
Think about this, if you use a 17” x 17” pc of 5 oz carbon to reinforce your cat, that cloth at 5 oz/ sq. yard should weigh in at 1.1 oz. That means you should use 1.1 oz of resin to saturate that cloth! How much resin have some people used in their boats? If you did 5 oz of resin resulting in a 5:1 ratio, that means you could have put down 3 properly saturated layers of carbon, or even two layers with a resin content of 67%!
Now, someone uses Kevlar at 49,000 psi TS and polyester at 9,000 psi TS and does a proper layup using 1:1 cloth to resin, they end up with a layup that has about 30,000 psi TS. Still below the wet carbon layup, I will give you that. But if the original hull is polyester, and it is unwaxed, it will make a VERY strong layup taking a lower skill level to pull it off. This used to be of great benefit due to cost. Well, lets look at that now….

Now cost.
Gotta admit, much of my thunder from above is gone when you look at modern pricing. OK, when I got into this carbon was pricey, about $50 a yard. If you go to the major supply houses, it is still in that range. Kevlar used to be much cheaper. I would buy a partial roll that was “seconds”. What that meant was that a strand in the fabric got tweaked or pulled so it wasn’t a perfect weave. Anyone ever try to cut Kevlar and see what it looks like when you’re done cutting it? It was perfect for me and I think I used to buy it for like $10 a yard. Built quite a few gas and scale warship hulls from that stuff in the past.
Now days, with Ebay and end of cuts for carbon, I do not think the cost difference is their anymore, or as great. I have to admit that I am kind of shocked at what I found on ebay. It seems you can find better deals on small pieces of carbon than you can on Kevlar. Hmm, maybe I need to go sexy…..
OK, seriously, sorry for putting that image in your mind. If you can find a deal, go for it. But two major things. First, do NOT use too much resin. And use a good resin. Two places that I know of and have used, is US composites and Fibreglast, both great places with good products. Second, do not discount polyester and Kevlar. Polyester on a polyester hull with carbon mat and Kevlar cloth can work fantastic. I am looking at making a little mystic cat at 20” this winter, I think I will start watching Ebay for some bargains.
Oh, just to add. Try multiple layers of lighter fabrics also. With the high strength of carbon, try a 5 oz layer of Kevlar topped with a 2 oz layer of carbon. Get the strength as well as the impact resistance.
Good luck, do your research and do not be afraid to step outside of the “sexy” box!

[NativePaul]

Epoxy is better and polyester is just cheaping out.

Tensile strength is only part of the story the flexibility of Epoxy is a large part of its strength, it may only be 10% stronger in tension but if it flexes and absorbs an impact and polyester cracks that figure has changed vastly in the favour of epoxy.

As to the wetness of lay ups I've skinned a few wings in my time and I will agree that without vacuum baging its neigh impossible to get the ideal 60% fibre 40% resin but it is relatively easy to get better than 50/50 just with a good squeegeeing with a credit card and dabbing with paper towel, but even those very wet lay ups (yeah I've seen them too) with 5 parts resin to 1 part cloth you cant just divide the cloth strength by the resin amount, in reality 1 part cloth 5 parts resin will actually be ever so slightly stronger than the same single layer with perfect 60/40, although it will be a HELL of a lot weaker than 3 layers of well wetted cloth that would weigh the same as the single layer that's too wet.

I have used 3 different epoxy laminating resins all bought in small amounts 1litre or 1kg from model shops and all have performed admirably with both glass and carbon, I only tried 2 of them with kevlar as to be honest I found cutting it too much of a hastle and stopped using it a while ago, only buying 1 batch and not even finishing that

[befu]

Yep

I do not think I disagree with anything you said. I love kevlar for its toughness, but working with it can be a pain! Once you get scissors that cut it, it isn't as bad.

It depends on what you want I guess. Epoxy is better. Heck I would love to drive a suburban like my wife, but I drive a small pickup because it fills the need. For many, polyester will work just fine. To be honest, the average hobby person will not do a layup correctly to see the true benefit of epoxy. Epoxy is my choice also. I just do not like people spouting that polyester isn't any good or it is garbage. Just because it isn't as good, doesn't mean it will not work. Epoxy is just better, not magical.

Brian

Epoxy is better and polyester is just cheaping out.

Tensile strength is only part of the story the flexibility of Epoxy is a large part of its strength, it may only be 10% stronger in tension but if it flexes and absorbs an impact and polyester cracks that figure has changed vastly in the favour of epoxy.

As to the wetness of lay ups I've skinned a few wings in my time and I will agree that without vacuum baging its neigh impossible to get the ideal 60% fibre 40% resin but it is relatively easy to get better than 50/50 just with a good squeegeeing with a credit card and dabbing with paper towel, but even those very wet lay ups (yeah I've seen them too) with 5 parts resin to 1 part cloth you cant just divide the cloth strength by the resin amount, in reality 1 part cloth 5 parts resin will actually be ever so slightly stronger than the same single layer with perfect 60/40, although it will be a HELL of a lot weaker than 3 layers of well wetted cloth that would weigh the same as the single layer that's too wet.

I have used 3 different epoxy laminating resins all bought in small amounts 1litre or 1kg from model shops and all have performed admirably with both glass and carbon, I only tried 2 of them with kevlar as to be honest I found cutting it too much of a hastle and stopped using it a while ago, only buying 1 batch and not even finishing that