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WHICH RESIN TO USE?? EPOXY vs. POLYESTER vs. VINYLESTER

More than 95% of all boats, truck & car bodies made of fiberglass are made primarily of E-glass, an orthothalic polyester resin and isothalic polyester gelcoat.

Therefore, items constructed with these materials should be repaired with the same or compatible material. LBI’s 301 orthothalic polyester resin is a good choice for most repairs. It provides a chemical bond to the existing laminate with similar strength & flexural characteristics.

Ortho polyester, isothalic polyester and vinylester resins are compatible, they all have styrene (commonly known as the “fiberglass smell”) and chemically bond to one another.

When higher strength, bond and water resistance is required (such as keel, rudder repair, or out-board transom replacement) use LBI’s 302 Isothalic Polyester Resin.
To achieve the highest bond strength and water resistance use LBI’s 901 Vinylester Resin.

Vinylester is essentially a styrene modified epoxy resin. It adds excellent strength, rigidity, adhesion, water and chemical resistance.

KEEP IN MIND

  • Epoxy adheres to wood much better than polyester does. To cover wood, a laminate using epoxy resin and 10 oz, cloth will yield a much better job than 10 oz. cloth and polyester resin. The epoxy/cloth laminate is comparable to using polyester resin with 3/4 oz. mat and 10 oz. cloth however the epoxy laminate requires much less labor to fair.
  • A polyester laminate job is somewhat less expensive in material costs than an epoxy laminate project of the same size.

REMEMBER

  • Fiberglass mat should not be used with epoxy because the binding material in the mat will NOT dissolve in epoxy resin.
  • Either mat, cloth or woven roving may be used with polyester or vinyester resin.
  • Since mat sticks much better to wood than does cloth, always make mat your first layer against the wood to be covered in a polyester laminate project.
  • We recommend using a layer of mat between layers of cloth for maximum adhesion between layers.
This Post Has 8 Comments
    1. Usually color, as the resins can come in different colors. Our poly resin is green, and our vinylester is orangish when cured.

  1. Hi there,
    I am currently building a 9mt power catamaran.
    I was thinking to lay down 2layers of 1000gr/m2 with epoxy in and out!
    Do you guys think it will be strong enough???
    Cheers
    Mark

    1. Hi Mark,

      We’d like to get a little more information regarding your catamaran. What are you going to be using as coring/framework? When building boats the coring does sometimes determine how thick you want to make your laminate.

  2. Hello. I just want to know. I have some polyester fruit decorations that sit on tables outside. So far, they haven’t cracked, chafed or split. Nor have their surfaces become weathered and dull. To prevent that from happening, what is the best spray on sealant??? I always like to find the “secret stuff” and the old “lost knowledge” when it comes to the products I buy. I once tried feldspar coating on a quatrz crystal. “The Kid” at Home Depot said it would work “fine.” NO IT DIDN’T!!!! Where have all the “Tool Time era “EXPERTS” gone!??! Man, we need those knowledgeable guys BACK again!!! Oh yeah, that’s right.. most of them are retired, and a good 70 percent of them are now living in assisted living facilities, today. Those were they guys who had the KNOWLEDGE!!! Today’s so-called “sales reps” don’t know NOTHIN!!! The feldspar turned my crystal BROWN, and it never did lose it’s stickiness!!! Good old “South Park style” stupidity strikes again!!! I also have a polyester Jedi light stone pyramid ( it’s better than calling it “orgonite” folks!*** ) on my front patio. I’d like to coat it, too. But I’m not about to ask another “college kid” what to spray on it to help protect it from the elements. Should I use Scotchgard? Sunguard ( which has sketchy reviews )? Castin’ craft’s polyester resin spray? ( If it, too, is made out of polyester, it may not provide very much protection! )? Or should I use that Aerospace 260 ( ? ) spray? The only downside to the Aerospace sealant is that it gives you a not-shiny ( matte ) surface, which is not at all desirable. I’ve heard that epoxy doesn’t adhere well, at all, to polyester or fiberglass. That’s unfortunate, because that would be a perfect shield for outdoor items made with polyester or fiberglass. There are also coatings that are used on automobiles, as well. Then, there are all of those “forgotten gems” that no one’s heard of in years. Boiled pine sap? Ol’ Timer Silicone Seal? Smith’s “Bond-aide?” “Plasta Bond Seal?” You know,.. the kind of stuff that was used on old aquariums 50 years ago that is STILL shiny and hasn’t yellowed or oxidized!!! As the country song says,.. “That’s The GOOD STUFF!!!”
    Any input or product references would be greatly appreciated. Thank you.

  3. I have a repair to make on the bottom of my 1997 38’ Chris Craft. The keel has been damaged (my friend actually thinks that the boat at one time might of been dropped , I’m not entirely convinced as it looks like the previous owner hit something) and the hull shows signs of vertical and round stress cracks. I am wondering what my best choice of resins and cloth would be. Not a big job but working lying down makes it difficult.
    Dimensions: area of keel 14” – 24” length by 1” – 2” wide x 1” x 2” high. Area of hull 3’ x 3’ x 2
    Plus’s Gel Coat and what ever else you suggest.
    My experience working with fiberglass – some above the waterline.
    Thank you in advance!
    Rick Senokosoff

  4. Ve resin or epoxy. Which one can not long lasting and become yellowis when expose to much under sunlight?

    Some epoxy have UV protection added into it. It is work to avoid yellowis?

    1. VE resin is generally formulated to be UV resistant. Epoxy resin will yellow in sunlight unless it has UV protection added to it, or is protected with a UV resistant coating.

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