What is difference between Epoxy & Polyester Resins

Hi Pamarine,

I wouldn't use polyester on wood either. If I used wood I would use epoxy. And it is not due to the fire hazard, epoxy loans itself better and does bond better to wood. If you choose to use the wood method then you would use epoxy.

The only time I would have wood on the boat is when there is a BBQ.

 

Sorry I got disconnected due to the weather here.

If you all agree with that there is such a big difference in performance between polyester and epoxy, then I would like to see some evidence.

Surely someone must have built two boats somewhere and the polyester boat btoke while the epoxy lasted, or the polyester whatever but the epoxy didn't.

You keep on hammering on the structures of the polyester vs epoxy, show me in real life that there is such a big difference.

All I see is people saying things but no hard evidence.

 

There are many polyester resin formulations as there are many epoxy resin formulations. Seems like the discussion is missing that. Early polyester boats which were built resin rich didn't blister. During the oil crunch, new resins started to have blistering problems. Also, companies like Uniflite, were building boats with milspec polyester resin. It is fire resistant, a good thing for the Vietnam era patrol boats. However, four or five years after launching they were getting blisters the size of watermelons.

 

Several posts have stated that selecting the proper resin for the intended use is key to good performance. IT really matters not if the resin is polyester, vinylester, or epoxy in this case.

What we are saying is pick any application and choose the best suited polyester resin and the best suited epoxy resin for that application, and with equal quality in the layup and curing processes, the epoxy resin will out-perform the polyester resin.

 

How many people here buy only "the best" product(s) for anything in life? Does anyone here live in the best house made with only the best materials and only drive the best car..... and on and on, its a compromise, we buy what fits the need, but you can always spend more and get better stuff.

Would it make a difference if my boats were made from epoxy instead of polyester, not really, except that I wouldn't be able to afford them. As far as how they get used and how they perform, it would have little affect.

I drive an F150 4X4, I could upgrade to a heavy duty diesel, because in almost every way its better, but would it make a difference in how I use it....not at all....it would only cost me more to buy it.

 

Your analogy would be better if you were comparing your 150 to a tundra or some other 1/2 ton. but anyway,

I always recommend someone buys the best they can afford, because in the long run it will save them money.

The OP was asking about making a repair to an existing FRP structure. Any epoxy that is available at a reputable Marine Supply Store will provide better mechanical adhesion of the repair to the existing hull.

 

The question was what should he use to do the repair, epoxy or polyester, in reality it will make no difference which one gets used, they are both up the job. You can under or over build with each one and as far as the bond, the prep work is the same for each product and while the bond with epoxy is better, the bond with Polyester isn't bad, its actually quite strong and durable.

 

Sorry to contradict you here,
that is just NOT TRUE! Not even the manufacturers of poly resins claim that it sticks well.

I really cannot understand why this idiotic statement pops up here ever and ever again.

Poly sticks good to nothing, absolutely nothing, not one single boatbuilding material, not even to cured poly, not to untreated glassfibre, just to nothing!

It does not stick!

And it is water permeable, no matter which one u use. Gelcoat is even worse than straight poly, it just looks nice (for a while).

Does anyone here assume we do our wood epoxy boats because we love epoxy? Anyone familiar with barrier coats? That´s epoxy. Why?

Please stop telling people which come here for serious advice, they could use poly for repairs. They could use plaster as well. (in fact that is done on wooden boats)

Regards
Richard

 

I have made many repairs with polyester resin. For example transom and stringer replacement in runabouts. It is the same way they were built. At one time we were doing maybe six or seven a week with no failures ever. They are not high performance, minimum weight hulls, so the repair is adequate.

 

Gonzo

would you say you are a novice?

 

I'm not sure how a Polyester Resin resin will adhere as well as an Epoxy resin.

For one, Polyester has a high shrinkage ratio during curing and will pull away from the repair, weakening the mechanical bond. (This is why Epoxy is used on aircraft)

The adhesion of epoxies (Maas. West, and System3 that you will find in marine supply stores) approaches 2,000psi or higher. Vinylesters are only around 500psi and polyesters are even less.

 

Polyester resin will not adhere as well as epoxy. The shrinkage, if any, is not significant in a resin rich repair. The styrene disolves some of the old resin and helps in the bond. The adhesion is adequate for some repairs. Epoxy has as much failures with amateurs as polyester. The wrong ratio or bad mix makes a gooey mess. I find polyester easier to work because the amount of hardener controls the work time. However, I would have to be really broke to do fiberglass work any more.

 

I agree with this completely

 

Richard, you seem to forget that time is marching on, and with it comes new technologies that makes things possible that were not possible before.

If I want to stick polyester resin to old polyester fiberglass then I can. Our local supplier sells a solution you wet the to be glassed fiberglass with. This makes the surface soft and it allows the new polyester to make a decent bond. I have not used it myself before but I was told by the supplier that it works so well it can be considered a permanent bond and will not delaminate. I don't know how many PSI's per whatever it will be.

Also, the boat I'm building will simply be painted. I don't see how water will seep into it. Even without paint a simple four layer glass only layup which is quite thin does not leak - from personal experience, one layer probably would, maybe even two layers, but I bet it's the same with epoxy.

A polyester repair does not have to be resin rich. For small layups I don't plaster the glass in place, I wet the glass then place it in place. There is no extra resin that is associated with the usual, well, I call it plaster where there is 100g glass and 400g resin. The resin does not add to the strength, only the glass does and the glass requires only so much resin to be at optimal strength.

The backyard mechanic that wants to fix his boat up buys a liter of polyester (any type that is the cheapest), some chop strand and sets off to replace the bulkhead in his boat or replace the rotten floor. He glasses over the old dry and when he hits the first wave the glass begins to delaminate. There's your problem. Polyester is crap and sticks to nothing.

I'm sorry you guys are so broke

 

Fanie,

You do need to realise that there is a minimum acceptable standard for a repair and that a properly chosen polyester resin will normally meet that standard. But we are talking about what is the best, not what is passable.

As far as the snide remarks, some of us have made careers out of composites, and the benefit of that accumulates knowledge should never be outweighed by anecdotal evidence.

When you start talking about "softening up" an existing laminate, you are then going beyond mechanical adhesion to a chemical bond. Chemical bonds will always out-perform mechnical ones with the same resin. But then again, you can only safely "soften" so much of the resin before the overall integrity of the structure is compromised.

And yes, I know that was addressed to Richard, but you attitude and post in general seems to be address many of us.