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Thread: Epoxy VS. Polyester

  1. #1
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    Epoxy VS. Polyester

    I've used West System epoxy extensively in, on and around Commander hull #215. In the five years I've had my boat I've gone through at least 5 gallons of resin and used all of the hardeners and fillers in that line. I've had nothing but good luck with West, and I think their literature is excellent and gave me the information required to get the most out of their high quality product.

    My remaining intrest in polyester is a result of the huge disparity in price and working properties of air inhibited resins. With West at about 100.00 a gallon for resin and hardner and laminating resin at $35.00 a gallon I'd like to see if I could get the same results with the less expensive product , after all, my Commander started it's nearly 40 year life as a polyester boat. Price aside, it would seem that for working overhead, repairing core and building laminates, that a resin that remained tacky on its surface would enable one to build layers up more easily and with a slower more complete mechanical bond the result. All this without having to wash the amine blush off and a frosty sanding. Less work!

    Does anyone know of a good technical guide for working with polyester resin? I have Paul Petricks book "Fiberglass Repairs", its pretty good but I'd like something along the lines of the Gougeon Bros. technical manuals. Can you use the same fillers for polyester as you can for epoxy? Anyone with info or experience, please weigh in on the relative merits of these two products, shared knowledge and saved money may be the result.
    Cheers B.
    Commander #215
    Last edited by Bill; 02-26-2003 at 08:47 AM.

  2. #2
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    exopy/poly

    i have heard that poly is good for above the waterline and epoxy below.

    probably because epoxy is more resistant to water, while poly forms a more complete bond (chemical and mechanical). the layers of epoxy only have an adherent mechanical bond, whereas a new poly layer will actually chemically bond with the old layer so that the two are one piece.

    there is an interesting aritcle on good old boat about this. i will try to find it or a web link. it also had to do with safety. the poly has fumes that are harmful, while the mixture isn't harmful to your skin, but the exopy is exactly opposite.

    i will follow up on the web address here soon.
    -km
    hull#3

  3. #3
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    I'm sure poly would work fine, but epoxy does have superior qualities.

    Here are a few articles I've collected:

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

    http://www.boats.com/content/default...contentid=2907

    West epoxy is overpriced. Raka or Mass epoxy is about $ 80 for 1.5 gallons.

    This guy sells epoxy for much less.

    http://www.epoxyproducts.com/marine.html

    I don't have any experience with his products.

    Mike will probably have a link to a good wholesale company.

  4. #4
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    sticky subject

    I have never heard that polyester chemically bonds to itself. Unless you are doing wet laminations with unwaxed poly.

    Polyester is NOT a glue.

    Epoxy is a glue. And if somebody wants to call dry layers of epoxy 'mechanical' so be it. My research says epoxy sticks a lot better to cured polyester than polyester does.

    The epoxy I used does not have a chemical smell. Has no solvents in it. Doesn't shrink, doesn't blush, cures at 40 degrees on up.

    Polyester styrene will kill you. You need 70 degrees for a successful cure. Acetone, your solvent of choice, and MEK will melt your brain cells. I would rather have a mechanical cure (what the hell is the matter with that?) than a chemical. What's that anyway?

    This is not to say that polyesters don't have their place in well ventilated work spaces for projects like seahoods, hatch covers and tanks.

    Please show us(me) where polyester is the prefered refit material.
    Polyester based vinylester is a better adhesive, used in molded boats as the first layer in the mold (I hear) But again, if it's a barrier coat after that fact you use an epoxy. It is more waterproof. Vinylester is used for handmade gas tanks, but it's because modern gasoline attacks epoxy.
    Last edited by ebb; 09-30-2015 at 07:36 AM.

  5. #5
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    Please, please use epoxy!!

    Please don't try to save a few bucks using polyester resin for boat repairs. You will very likely be sorry later! This is penny wise and pound foolish.

    Polyester may be fine for new construction, but for repairs to existing construction you need the "secondary bonding" capability of epoxy. Like Ebb said, epoxy is an adhesive resin, while polyester is not.

    Polyester works well only with primary bonds--that is, the chemical bond that forms when layers are added within the "green" working time. Once this brief window of opportunity has passed, the bonds will not be particularly strong. The same goes (especially) for bonding wooden pieces with polyester--wood and polyester do NOT like to stick together for any length of time.

    No one ever said boat repairs were cheap. You still have to use the right product for the job. For most boat repairs, the right resin is epoxy. It doesn't have to be West System--many of the other epoxies are also excellent. Each system has its own unique qualities, strengths and weaknesses, however, and each is slightly different to work with. West System is an excellent epoxy, but my no means the only one out there. Amine blush is, to my way of thinking, an extremely minor thing to worry about--it's very simple to scrub with water and Scotchbrite pad, and once it's a habit you don't even think twice about it.

    Unless you are laminating on green resin of any kind, you are getting only a secondary bond. Once the green stage is passed, you need to choose the product that will give you the strongest mechanical, or secondary (adhesive) bond.

    Don't mess with this. There is a difference between poly and epoxy, and it's a very important one for this application.

    Personally, I didn't like MAS epoxies when I tried them--I had trouble with incomplete curing, among other things. I have never experienced a single problem with West System--it always works exactly as intended. Also try System 3 or Raka. Buying the small cannisters of West System filler products will break your budget in a hurry--you can buy any filler in bulk from Raka or System 3. They are the same thing, and also work with polyester (not that you should be using poly!)

    Tim

  6. #6
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    For one thing , it's not polyester resin anymore , it's vinylester resin , it looks and smells like poly and uses the same hardener.
    You can still get poly , but why would you . Even Gougeon admits that vinylester is more waterproof than epoxy .
    I have worked with the 'esters' for 40 years now .
    Epoxy is no better than poly , as beer is no better than wine .
    The library is full of books about poly resin construction .
    There are at least 5 varieties of the poly group with vinylester at the top , the $15 a gallon poly at the bottom .
    Epoxies are so divided by hardner ratios , from 1:1 to 1:7 . 1:1 is the cheapest and least toxic , 1:7 the priciest and most toxic . Strength and waterproofness varies greatly (the most waterproof is not always the best or what you need ) . Almost all brands of epoxy use the same basic resin , it is the hardners that make the difference .

    Good workable epoxy & poly can be purchased from;

    fgci.com

    I pay $65 fo 2 gallons of 1:1 , for a barrier coat you want 1:3 to 1:5 . 1:1 is fine for laminating , sheathing a wood boat with glass or interior and deck work .

    There is nothing wrong with WEST System except the price , it is like CocaCola ,marketing and name recognition .

    With epoxy you can get real bad dermatitis and some lung disease .
    I am living proof of what can happen from long exposure to 'poly', 2 bouts of chemical blood poisoning , the last nearly killed me .

    A good ( $$$ ) respirator is necessary and always work out doors or if you are in the cabin with 2 fans , one in & one out .

  7. #7
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    Tim,

    I covered a dinghy with poly and glass , it lasted for 21 years of constant exposure to the southern sun & saltwater .It may have lasted longer , but was brought to an abrupt end when a trawler pinched it between itself and a dock .
    Poly is not a glue and should not be used as such , but as a laminating layer is is equal to epoxy , now that epoxied boats have been around for 25 years people see that it is not the panacea we thought it was in the late 70's . Good boatbuilders and repair yards use both .
    Epoxy has one fault that poly doesn't suffer , thermal breakdown when used topsides under dark colors .

  8. #8
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    Great cautionarys here from guys who have used this stuff. One more bit from ebb on epoxy. I have not used West System. The reason is that the System uses cheap carcingenic extenders. (nonyl phenol - MDA) These extenders cause the blushes. A blush is a WAXy film. These extenders cause cancer. OK? Why put up with washing your work when you can buy a better product?

    The epoxy you use should ONLY have a FAINT toasty smell (from the amines) I too became allergic years ago to the amines where it attacked the fingers at the nails. Gee! I learned to use latex gloves.

    The key words for epoxy is:

    100% solids.

    If it don't say that it's not good, No matter who told you or how well you have aclimatized your poor self to some corporation's (profit) system. Really! DO NOT USE IT, even if it's made by cocacoli.

    If you had epoxy shipped to you and they had to hazmat, you bought the wrong stuff. See ya! (hope so)
    Last edited by ebb; 02-26-2003 at 02:14 PM.

  9. #9
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    poly/epoxy

    i found the website. oddly enough it was buried inside an article about building tanks for sanitation.

    http://www.boatus.com/goodoldboat/sanitation.htm
    you have to scroll down a bit, but there is a side bar by an ER doc about poly/epoxy, safety and chemistry.

    but i plan on using epoxy when repairing any hull dings during my hull refurb.

    -km
    Hull#3

  10. #10
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    With 3-M vinylester putty , you can be sanding those ding repairs in less than 15 minutes of application . That is what most pro marine paint shops use . You can use epoxy if you want and you can marinate hamburgers with a $300 bottle of Merlot if you really want to . I'd save if for sipping with my lady .

  11. #11
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    how rumors get started

    Not quite sure if this is worth the time here but....
    Doc Parker in mrgnstrn's ref gets his info on the epoxy he talks about from who? Gougeon Bros. He briefly says "epoxy dust is toxic if inhaled."
    As a reader of this your only assumption can be: it's Gougeon Bros epoxy dust that is toxic. Right?
    First off: the good doc presents no evidence for this statement, and it is therefor, hearsay.
    Second: inhaling any dust (while it might not be exactly toxic) is bad for your lungs - you should always wear a dust mask when sanding or grinding, even the fuzz off a peach.
    Third: if epoxy when cured is great for potable water and all manner of food containment, what is toxic? If the good doc's info comes from Gougeon Bros - who do use 'toxics' in their epoxy formulas- don't use Gougeon Bros epoxy for your water tanks. THAT IS THE MESSAGE.
    Fourth: beware of advice from masked men in blue pajamas.

    Paul Oman's epoxyproducts site is IMCO the premier source for info the subject. There's just the right formulation of non-toxic erascibility, honesty, and intellect for unpredjudiced information. In the past he has returned email questions of mine. It's a good site. IMCO
    Last edited by ebb; 02-27-2003 at 08:33 AM.

  12. #12
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    As far as I'm concerned, all of this stuff should be treated as toxic.

    Acetone is probably the worst. It eats through regular gloves and makes your eyes water even with a respirator on. Must be real bad.

    I'm curious about Dr. Mark's statement that poly adheres better to poly than epoxy does. I'm not so sure about that.

  13. #13
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    From the latest BoatUS flyer
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  14. #14
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    poxy

    Yeach, I think it's this guy what has a project book published that uses polyester for everything inside and out on an existing boat.

    You can do it to save money (blub blub blub) and to assure adhesion you have to grind with 36 grit (gee, 24 and maybe 16 grit will be even better!)

    The cheapskate drowned and/or the grinder died from polyesterosis.

    What he describes in the first paragraph for polyester is even more true for an epoxy 'lay-up.' You can get yer bloody 'chemical bond' just as easy, in fact much more easy and safely, with 100% solids epoxy. Just put one layer on top of the other, wet it out with epoxy - wow, and no waxey top coat. Epoxy you probably should create some tooth between layers if it sets up. That's right, but you don't need to grind.

    Use Epoxy. Use the best epoxy you can get. At least Mr C. sort of implys there is a guarantee with the pricey stuff. But you'll always be wondering about the cheap stuff. IMCO


    Years ago a planked 8 X 29' gaff rig sailboat I had was glassed with cloth & polyester. I must have let it go overnight or maybe even days between layers. It never failed so far as I know. So I will defer to the experts here - I don't know modern polyesters - as long as you don't put the finsh coat on you can come back to it later. How much later I don't know. The project is 'wet.' With epoxy, you can repair things, smooth and fillet, cut and shape, come back and add more layers. Much more versatile and forgiving.
    Last edited by ebb; 03-15-2003 at 07:58 PM.

  15. #15
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    Exclamation Danger! Danger! Danger! Will Robinson!

    While working on my dingy Sunday, I came upon a particularly difficult substance to remove. I was coating a piece of ply in epoxy and mounting it to the transom for the motor, and there was a 'goo' that acetone would not remove.

    I went to MEK, that I found in a rusty can in the flam locker, and it worked.

    I remember years ago, that I had decided MEK was a substance I would no longer use, (something about being absorbed through the skin and there being no means for the body to excrete it) so I went online this morning to refresh my memory.

    Came upon an unrelated piece of information about MEKP

    Methyl Ethyl Ketone Peroxide that is used to cure polyester.

    Apparently, if it is exposed to acetone, the results can be drastic. Kinda scary considering the two chemicals are regularly used, and stored together.



    Note to self. Don't store poly catalyst and acetone together.


    Here is where I found this, fwiw
    Link to discussion of hazzards of MEKP



    Any thoughts Ebb?....

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