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Thread: Resin selection...

  1. #11
    Senior Member LP700-4's Avatar
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    Quote Originally Posted by bartman View Post
    There are only two types of bonds in composites. Cross link and mechanical. The reason to use the same kind of resin is to achieve a cross link bond. Polyester is fully cured and will not cross link after a few days. So, all that is left is a mechanical bond. Unmodified polyester resin has a very, very poor mechanical bond. That is why when you look at a boat for instance, even though the boat is made of polyester, they do not use polyester to bond in the stingers, or the upper deck to the hull. All of these have "lock up tight" and there are no free molecules to cross link with the new polyester. Epoxy has a very high mechanical bond strength but will require higher temps than what you are talking about. Like I said there will be a lot of opinions but there is no valid reason to use the same resin system unless you are looking to cross link to the previous resin which would have to occur within 48-72 hours, max. A lot of my parts are built with ISO/DCPC hybrid (isophthalic polyester/dicyclopentadiene) and it will not bond to itself the next day. Sure it looks like it does but the joint will fail within months.

    Bartman,
    Thanks again for your recommendation. I am picking up some West System epoxy this week.

    Here is a link from the manufacture discussing this for those who still dont think you should use Exoxy over Poly...

    http://www.westsystem.com/ss/west-sy...rglass-repair/
    -Glenn

    "One day I had a bit of an argument with my friend Enzo Ferrari, who reckoned I wasnít able to drive a Ferrari, only tractors. Thatís when I got the idea into my head and told myself Ė Iíll make the cars myself from now on!" - Ferruccio Lamborghini

  2. #12
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    My advice would be best to stay with Poly, it's easy to use and the bond if done properly will be fine. Epoxy resin can be tricky to use and not really novice friendly.


    Don't get me wrong I'm not saying that Bartman is not correct and he is giving good advice just not sure it's best for your application. Anyway have a go and lets see the results in due time.

  3. #13
    Senior Member newtomm's Avatar
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    Let's remember what the repair is for ! It is merely a cosmetic fix, It most likely will not be submerged under 30 feet of water for prolonged periods of time , unless I missed something in the post ! I have been producing and repairing fiberglass with vinylester resin for 25 years and have never had any problems with bonding on any of my repairs. Make sure that the area is ground out and back in a wide V and use different layers of matt getting larger as you proceed. Then Grind the top side the same way , repair the same way and you will be good. I first used some epoxy after having about 10 years experience with Vinylester and found the epoxy difficult to work with.
    I would not recommend epoxy for a beginner or novice . Just my 2 cents

  4. #14
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    Sounds like Bartman really knows his stuff and is giving some good advice. Composites really are a huge subject. Polyester would be fine for unstressed FG panels, if you took it to a pro shop they would still use Polyester and it would be perfectly fine. Something to keep in mind too is don't use too much hardener, if it goes off too quick you won't get good wetting of the mat and it will end up brittle. Also regardless of what you use don't use more than you need, you only need enough resin to effectively transfer load from one fiber to the next, any more and it's just weight. Anyway your question was answered long ago but it's an interesting subject

    Oh and before I forget, epoxy over Poly is fine, Poly over epoxy is not such a good idea. The area in contact with the epoxy won't completely cure so keep that in mind for future repairs if you want to use poly again.
    Last edited by justincosgrove; 02-02-2016 at 10:53 PM.

  5. #15
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    Quote Originally Posted by newtomm View Post
    Let's remember what the repair is for ! It is merely a cosmetic fix, It most likely will not be submerged under 30 feet of water for prolonged periods of time , unless I missed something in the post ! I have been producing and repairing fiberglass with vinylester resin for 25 years and have never had any problems with bonding on any of my repairs. Make sure that the area is ground out and back in a wide V and use different layers of matt getting larger as you proceed. Then Grind the top side the same way , repair the same way and you will be good. I first used some epoxy after having about 10 years experience with Vinylester and found the epoxy difficult to work with.
    I would not recommend epoxy for a beginner or novice . Just my 2 cents
    Vinylester is not the same as polyester. I use AME5000 for some molds and some AME6000 for a few infusion parts I make for another industry. Vinylester does have good bond strength compared to polyester and adheres to itself really well and part of that is because it does not lock up at tight or fast as poly. Vinylester and polyester are two very different resins even though they both are catalyzed the same. If he has access to vinylester, it is a good choice but to non composite shops, small quantities may be hard to get, I don't know, I've never tried. I get 55 gal drums.
    Last edited by bartman; 02-03-2016 at 01:08 PM.

  6. #16
    Senior Member newtomm's Avatar
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    I am NOT a chemist or an expert in fiberglass resins

    Quote Originally Posted by bartman View Post
    Vinylester is not the same as polyester. I use AME5000 for some molds and some AME6000 for a few infusion parts I make for another industry. Vinylester does have good bond strength compared to polyester and adheres to itself really well and part of that is because it does not lock up at tight or fast as poly. Vinylester and polyester are two very different resins even though they both are catalyzed the same. If he has access to vinylester, it is a good choice but to non composite shops, small quantities may be hard to get, I don't know, I've never tried. I get 55 gal drums.
    I have been dealing with the following company for 15 years, and they have experts in their field of Resins and fiberglass. http://www.fiberglasssupply.com/Prod...er_resins.html
    Listed in their selection of polyester resin is Vinylester resin !
    I buy resin in 55gal drums , specialty resins in 5 gallon pales and others on quarts. This company sells 2 oz. bottles of MEKP catalyst. This company will take your questions, evaluate them and suggest what they have many years experience of what will work best.
    I would give them a call, They will ship you anything, BUT they are more concerned with getting you the correct product for Your application. They will not steer you wrong. Check them out on line and then give them a call. They are on the west coast, so they are open a little later in the day if you are in the east.
    Phone 509-493-3464

  7. #17
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    Out gassing from Vinylester resin is a lot nastier than poly it can make you feel nauseous and sick, you must have ventilation. Would also need a slow release MEK that gives you about 45minutes @ 25 degC. Always look at the safety data any of the resins that are to be used, composites can be very dangerous to your health, also storage must be safe, keep MEK or any catalyst away from the resins at all times if they mix it could start a fire very fast. Know and understand how to put a fire out using these types of resins.

    Have a register of what you have in storage even if its in small quantities you should know what you have in the shed just in case something happens you can let the fire department know what's in the shed.
    Last edited by racecomp; 02-03-2016 at 04:05 PM.

  8. #18
    I have a lot of experience with resins. you can't do a repair with epoxy on a polyester part unless you add a layer of vinyl Ester first then cotton flox and the you still might have problems with getting the epoxy to adhere. if it's a poly part you must use poly or vinyl and Don't think because it's odorless you can use its safely in your home. that was horrible advice so please do not do this in your home unless you don't mind having a coat of epoxy all over your walls and skin at all time. epoxy is more dangerous in different ways than polyester or vinyl Ester. It fools you with its odorless strength but it's more dangerous to inhale or get on your skin which doesn't mean it has to physically touch your skin. there is enough in the air when working with it that it will seep into your skin especially when its hot from the fumes floating through the air.

  9. #19
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    hel;o gello

  10. #20
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    You are going to get a lot of opinions. Beware of those that "read" something and think they're an expert. If you are repairing or modifying, the most important issue is bond strength. Use epoxy.

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