What is difference between Epoxy & Polyester Resins

Hi-

I'm a neophyte to any type of fiberglass repair. i have a couple of cracks in the hull below waterline. I started a thread about those recently. Some folks mention epoxy others polyester resin. I have no experience with either.

What I do know is that outside temperatures during the day are in the mid 50's currently and at night are dropping to the mid or low 30's. All the work on the boat fixing said cracks will be outside.

I kind of walked away from the reading that the Polyester resins might be better. Hoping some of you will expand on these and give me the positive and negatves of each.

Thank you.

Have a Great Day,
Jim

 

For the novice, epoxy is much easier to get good, reliable results. In these temperatures you'll have to warm the area and keep it warm for several hours. This is easy enough with an electric heater and a tarp taped to the hull.

Log onto www.westsystem.com or www.systemthree.com and check out their user's guides about filling cracks, mixing, using fillers, etc. You can also use the search tool here and go through previous posts about epoxy use to get the information you need.

 

Fully concur PAR. Might just add, rising the temperature is needed for both resins.

Richard

 

There are quite a few epoxy hardeners to choose from, each working best at a particular temperature range. West System must have four or five temp ranges at least.
Actually, slow hardening can be ideal because recoating requires sanding unless the previous coat is still green. In that case, a chemical bond can still be achieved.
In cold weather, it's possible to do a good sized area and to know that you can continue with another coat within 24 hours, for example. This slows the work enough for a one-man shop to keep up.
Sometimes, of course, it can seem to take forever, particularly on a small repair. Luckily, epoxy can sit for ages before hardening, and as long as the ratio was correctly mixed, when warmth eventually arrives, the epoxy kicks.
If you miuxed too much, in other words, stick it in the freezer.

 

My personal opinion.

Polyester is far less pleasant to work with than epoxy. It tends to set up much faster, and stinks so bad it will burn your nose hairs out.
It doesn't have the water resistance of epoxy, but has it's uses. I replaced the cockpit sole in a friend's sport fisherman, and used 2 coats of polyester on the underside of the plywood panels before cutting and installing - this saved some $ on epoxy costs. On the walking surface I used MAS epoxy and glass, and painted with a good enamel with non-skid additive. Ten years later it has held up well. After much use the boat itself is about shot, so the surgery was well worth it.
I just looked over your other thread.
From what I can see in the picture, the break has significant overlap. Your choice is to try to push it out, or to leave it and fair it as-is. That will be up to you, based on how difficult it is to push out.
After sanding all the paint away underneath (go well beyond the area of repair so you don't apply epoxy over paint), I would apply epoxy with Cabosil and chopped glass strands as a thickened paste, in the depressed area to bond the broken section. Be sure to work it into the crack. Apply this like a first coat of spackle with a 6' plastic spreader, nice and smooth, but not beyond the depressed area. I'd then apply a heavy glass cloth or glass mat, and 2 coats of plain epoxy, followed by a last coat of epoxy with microballons or other fairing compound so you can shape and sand it all to your liking.
If you can access the bilge above the repair, I would reinforce the fix from the inside as well. Rough up the surface well with a sander so the epoxy will bond, and apply glass cloth or mat as below. You probably don't have to be as fussy appearance wise, but a bit of paint here wouldn't hurt.

Read all you can about the use of epoxy - mixing, cure times, how to wet out cloth, chemical and exothermic hazards, etc. - it's not that complicated or difficult, but there are some rules to follow strictly. Avoided skin contact, especially with the hardener, and be sure to wear a dust mask and goggles.
Good luck.

 

Hi Jim,

There is nothing wrong with polyeaster resin or epoxy. The main difference is epoxy is 5 to 6 times more expensive and epoxy takes about 24 hours to gell properly.

Polyester cures much faster which is temperature dependant more than epoxy. If you can keep polyester below 15 deg C you have a longer work time than we have here. In hot conditions I have about 15 mins max before the polyester gells and you cannot shape it any more.

Polyester is more smelly, but you have to work in a ventilated area in any case. Epoxy irritates the skin and a lot of people develop an allergic for it. I have been working for 25 years plus with polyester and it burns your skin but no allergic reaction I know of. I actually like the smell, it is not unpleasant in a ventelated area.

Keep a solution of washing powder and cool water handy to wash your hands in often and a rag to dry with and you will be ok.

Performance wise there is little difference between epoxy and polyester, I personally prefer polyester. Stick to the required hardner to resin spec, mix small volumes at a time and you will be ok. Polyester resin cures much faster if you can put it in direct sunlight, I suspect it is the UV that cures it faster.

 

An interesting thread. As a fiberglass dilletante, I have found polyester easier to use in many of the little repairs I have done. Epoxy seems better on paper but polyester done with modest care has worked out quite well in the field.

I find it easier to wet out poly and for me, for the little things I do, that is a critical component of a successful application. Cost is of little matter as I have sufficient quantities of either on hand in "ships stores" to tackle my modest projects.

I am interested in the tips and techniques mentioned regarding epoxy. I'm all for using superior products and respect the views and the experience of several who have posted here. I find the quicker curing times of polyester to be helpful, yet cheerfully acknowledge my relative inexperience with epoxy.
I'm not sure if this post is worth the customary two cents but there you go. Perhaps I may glean a few new arrows for my boat tending quiver.

 

You can talk to Manie if you want tips on epoxy, he has done a lot of experiments to get layups on one another right. Resin does not have the same 'isolation' trend, but you have to make layups in one go and before the resin or epoxy cured. I never trust any job especially big parts that gets done in multiple sessions. Any part should be one integral glassed part, no joins after it has cured if you can help it.

There is no superiority between epoxy and polyester. I checked some spec sheets recently and I was quite happy to see that polyester can actually outperform resin. That said, remember both epoxy and polyester come in different grades. So I won't put my head on a block as to which is the superior.

The deciding factor what you want to use is probably the method you are going to use and what it is you are about to do.

 

It makes little sense to lay up a hull using epoxy. Polyester sticks very well to itself. The cost is substantially less and the physical properties of polyester allow for light and strong structures to be built.
Epoxy is an amazing water barrier, and also an amazing adhesive. Because of this, there are places aboard a polyester hull for epoxy, especially as a barrier coat to prevent blistering of the underwater hull, something that can pretty much destroy susceptible layups if not caught in time.
Stringers and webbing/tabbing and bulkheads (particularly down in the often wet bilge area) do a lot better over time if they are sealed in epoxy prior to being installed.
It's not necessarily a choice between the two resins, but a selective use of both that makes the most sense. Rather than competitors, they are really different products for different jobs. Sometimes the two can be interchangable, depending on many factors such as level of familiarity, budget, expectation of longevity, and whether or not it is already on the workshop shelf.
Only experience and the study of available information over time can hone one's ability to choose right each time. Otherwise, asking here on the forum is great for doing projects on a case by case basis.

 

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.
Both resins Poly and EP should (no MUST) be applied in one go, to form a mono - molecular structure. And only that has the max. technical properties. Letting one layer cure before laying the next, produces a onion, not a boat hull! No matter how much and good you sand it.

From a pure technical point of view Poly is NOT a boatbuilding material! It is barely sufficient, thats it!
The reason for the industry to use poly instead of Epoxy is simply the price difference. Period

Alan

the statement that your matrix will cure month after mixing is not valid in any case! Some mixtures do not cure thoroughly after sitting cold for a long time, once curing had begun.

Jim
For the intended use there is only ONE choice, Epoxy. And the cheaper way it is too. If a novice makes a mess and has to do the job twice, he pays several times the price difference between Poly and EP. Which btw. is´nt 5 to 6 times Fanie, and both are resin!

Regards
Richard

 

Jim - the above has been my experience as well.

This can all be rather confusing, especially in light of the fact that all of the statements presented here concerning both products are true in certain circumstances.
This is why I recommend reading up on it.
Glen-L published a book many years ago, which instructed on the use of epoxy in boat construction. It was my first guide, and a good one. Apparently it is now available on a free online page, containing at least the salient points. They are naturally promoting their own products, Poxy Shield and Poxy Grip, which are fine products, but if you substitute that name for whatever brand you choose the directions are the same: http://www.glen-l.com/supplies/pxman-content.html

 

Come on polyester not a boatbuilding material. What are the millions of floating objects with a high percentage of them decades old?

 

Crap........






ok, ok, maybe I´m a bit biased........

not much though. Have you ever seen a demand for this?....http://www.gelplane.co.uk/
on a Epoxy surface?

 

I have seen them used a couple of times. I use an industrial sandblaster to take care of blisters. With the planer you still have to go back with a grinder to clean the holes. There is some myth going around for years that the sand will cut the glass fibers when the hull "works'. Glass fibers are silica like the sand. And whatever little dust is left behind gets mixed with the resin.

 

Hähähh.................
I do´nt care of blisters..............