What is difference between Epoxy & Polyester Resins

[Fanie]

There is for sure no doubt, Epoxy is by far the superior choice in ANY case!

Polyester is water permeable, Epoxy not. Poly sticks to nearly nothing, Epoxy to almost everything. Poly has to be mixed in extremely narrow proportion, Epoxy is a bit more forgiving. Poly has a short shelve life, Epoxy not. Means your dealer can sell you old poly cr.p that does´nt cure properly.

BS Richard The samples Manie gave me delaminated as easy as the polyester did which was new on old. Polyester resin has the advantage that you can chemically 'melt' the surface to make a good bond. Imo not desirable, as a matter of principle I like my stuff in one piece, even if I was using epoxy I won't do it any differently.

As for boats out there Richard, for every old epoxy boat I can show you a polyester one. If I'm not mistaken then most boats are polyester, even old ones.

The ONLY reason epoxy is used is because of it's viscosity and prolonged gell time - hence you can vacuum inject easier with epoxy. As I said earlier the spec sheets I compared does not tell stories or thumb suck. I have never seen epoxy used in a mould. The method determine the choice of material.

Just because the price is more expensive does not mean it is a better product. Epoxy is used for it's properties as I mentioned above, not because it makes a better boat or because it will last longer, or because it holds water out better. The epoxy or resin is only the binder for the glass and neither epoxy or resin contributes much to the strength of the glass. Of the same ratio to glass resin and epoxy is applied the results will come out very much the same.

If you seal wood then epoxy should come out better, again because of it's viscosity, it should penetrate the wood deeper. Glass only I can tell you that the results will come out very much alike in all aspects.

Shelf life on polyester, if the conditions are not radical then months. As for the calculation of the resin hardner ration I haven't had a problem with that either.

Just becaus you guys are snobs doesn't mean your expensive epoxy boat is better

[Fanie]

Oh yeah, I forgot to mention another drawback with epoxy. If the lightning hits your boat directly, you will have a good chance of the epoxy being evaporated. They have this propblem in epoxy built earoplanes, hence the shield that gets glassed in between the layers

Fanie

sure you know I build in both materials. Yes you did.

And EP does´nt penetrate deeper than Poly. It just sticks twenty times better.

Regards
Richard

[wardd]

http://www.redrockstore.com/resin.htm

[Fanie]

You can use polyester resin only with glass, it does not work with carbon fiber. Epoxy work with other than glass materials.

Hi Wardd, I saw that article before. I am talking about my own experiences. There are things some critics mention that I do not always buy like 'resin is used where weight is not a concern'. If the glass vs resin and glass vs epoxy is the same the weight will be very little different. It is again, the method of application that makes the difference.

The other thing mentioned is the scrinkage. Tbh, if resin scrinks, I haven't noticed before, but then I haven't built things the size of a soccer field.

I have seen some pretty old resin boats, like in really before my time - and that said I may not be as old as some of you guys. They weren't disintigrating and they were probably what, 70 / 80 years old. May not be the best hull design I've seen, but nothing wrong with the material. If there was problems with the lifespan of the materials then we would know it and authorities would require hulls beyond a certain age be scrapped. This does not exist.

If I build a boat that will last only 50 years I won't have a worry in the world Btw, how old is your car

I wonder how old a boat can get.

If you ask me then the sales people all say epoxy is the better because it is more expensive. When do you make the most money - if you sell at $20/kg with a 40% markup or when you sell at $120/kg with a 40% markup ? I have yet to see a salesman unhappy when you pay more.

[gonzo]

Fanie: I was saying about polyester being a good material. Go fight with
apex1

[Fanie]

I have some samples Manie made up for me a while ago in epoxy. Looking at it and feeling it's stiffness and flexing it I can see very little difference. If I didn't know it was epoxy it could just as well have been resin.

Polyester attacks some materials like polistirene and certain plastics which epoxy doesn't.

Fanie could we be so nice and use a correct terminology?

Polyester is a resin and Epoxy is a resin too.

Thanks

[Fanie]

Fanie: I was saying about polyester being a good material. Go fight with apex1

Corrected. El typo there. And I'm not fighting with anyone, but lets get our facts streight

The pic is a layup Manie made with epoxy. The epoxy delaminates the same as polyester does. If I didn't know it was epoxy it could just as well have been polyester.

See, I even got my finger stuck in there

[Fanie]

Ok, one last thing. The guy who does my boat parts strength calculations does the calculations purely on the basis of the amount of glass I use. He has never asked if I used polyester or epoxy. If this was a factor in any way he would have mentioned it to me for sure. They are professional fiberglass builders and work with various materials, and since they do the calculations for me for free (cost me the phone calls though) they have no reason not to give the correct information.

What does make a big difference in stiffness and weight is the type of material you use, carbon is lighter than glass (I felt that , and it makes your pocket a lot lighter too) and the orientation of the glass (or other materials) does determine the stiffness in a direction.

So, if I am to patch a piece of glass in somewhere, like Par said in the first post, I would firstly consider polyester. If I want to make something in a mould hand layup, I would use polyester. If I was to use a vacuum injection process, I would use epoxy.

Some people want to use epoxy, fine. Others prefer polyester - like me and I'm stingy so I want to pay less for the same thing - also fine. The thing is going to be the same in any case and like cars, the best one is the one you have and use.

Fanie
that was most probably glass with a silan treatment in Manies example! Thats good for Poly (`cos poly sticks to nothing, not to glass either if not prepared), but it makes a bad surface for Epoxy!
A perfect designed and executed Epoxy layup cannot delaminate, no matter on glass, Kevlar, carbon or wood.
Before the next contradiction pops up: PERFECT I said! Nothing less you shoul expect from your builder. (so, do´nt buy mass produced Poly boats, that is not even near to good, let alone perfect)

And I do´nt argue with your building method! I do´nt say that Poly is weaker then Epoxy, but it IS water permeable, there is absolutely no doubt possible! And when your gelcoat gets cracked, you have issues, there is no doubt also.
The fact that there are 50 years old boats still afloat does´nt make it a better material. (older than 50 are just 5 or 15, the method is´nt much older)
There are wooden boats out there which are over 100 years old! But thats a completely different topic. Until the late 70ies Polyester boats were so extremely heavy overbuilt (most of them), with a "fear factor" of 3 to 5 that it was hard to destroy tem.
And of course you CAN build a boat from EP in a mould, and it is done when other materials as Kevlar or Carbon are involved. Because then the price difference in EP to Poly is not much a factor anymore.
We will never see EP in mass production, its just the price what makes poly a material of choice.
But for sure it is the inferior in every case.

Regards
Richard

[Fanie]

I can accept that. Each one have their 'rules' to work by, ignoring them would be stupid. My wife doesn't like the almond smell of polyester, I do.

Just the mention of fiberglass makes some of my 'friends' itch, no wonder none of them want to help me build the friggen boat. The pictures of guys catching fish from boats does excite them though I bet they won't be late or have urgent stuff to attend to when the time comes.

A bit like you have lots of friends when you have booze in the house and few when you don't.

Reminds me I think it's time for the old witch to bake an almond cake for a change

[PAR]

Doesn't arsenic smell like you've cooked up some almonds? No wonder your wife doesn't want anything to do with it. She's afraid of you Fanie!

Just to get into the mix, all the polyester resins including vinyl are weaker then epoxy. When you look at elongation, compression, tensile, peel strength, hardness, etc., epoxy is far better. There's no debate over this, it's well documented. From a mechanical point of view it's fairly simple to understand once seen at a molecular level.

Think of the polyesters as a plate of spaghetti, some intertwining, but most of it just laying on top of other long polymer chains, it's this very thing, a two dimensional cross link, that limits it's peel strength. Epoxy on the other hand looks like the same plate of spaghetti, except the strands of pasta are all intertwined and better still, they have more then just two ends. They have many ends, all intertwined or bonded to other spider like molecules. This 3 dimensional linkage makes it much stronger, resist separation and penetration to a greater degree, etc.

Polyester is used in situations where strength to weight ratios aren't that critical. You can just bulk it up until it's strong enough for the tasks. When strength becomes more important and/or more chemical resistance and bond elongation are required, vinylester is a economic option that will fairly closely match some of the high tech fabrics available today. When interested in more strength to weight ability and matching resin to fabric physical properties, then you don't have a much of a choice, epoxy is the answer.

From a novice user's view, I think epoxy is a much easier product to get a handle on. You can screw up over a wider range of conditions and situations, with some level of success, which pretty much describes the usual novice's repair attempts.

Thanks Paul,

as always, you brought it to the point.
But you have it easier to express it clear. I´m not so familiar with the typical Spaghetti pattern.

cheers
Richard

[Fanie]

Can someone give me an indication of the difference in strengths between say 10 layers of glass, one with polyester and one with epoxy, applied same ratio and same glass. Also indicate the grade of polyester and that of epoxy.

Thank you.

I wonder why a layup's trength is determined by the glass and not wether you use polyester or epoxy.