Problem - and solution?

Discussion in 'Boatbuilding' started by caribmon, Jul 14, 2006.

  1. caribmon
    Joined: Nov 2001
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    Location: Netherlands - Brazil

    caribmon Junior Member

    Scenario...

    First layer of cloth and vinylester about to go on below-the-waterline foam... strongback straight, good start.....

    Problem.

    Builder has never used vinylester before, runs no tests, and lays up glass.

    Vinylester does not set (no cobalt for a start). His supplier gave him shoddy directions on the use.

    In a panic, builder starts spraying activator directly on with spray bottles. Still soft....

    Solution of builder is to lay a coat of polyester resin over soft uncured two day old vinylester resin and cloth.

    It finally hardens.

    Finishes job with Vinyester over Poly.

    How long do you think it will take before the skin pops from the foam?

    I give it three years tops. Could happen anytime in rough weather. This is an 'offshore' boat.

    Opines?
     
  2. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    The solution is to quit pouring good money into a bad boat. The first layer of vinylester never hardened. Mistakes happen, about the only thing there is left to learn from this one is when to quit. Sam
     
  3. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    I give it two, maybe three months if it's being used offshore like that.

    When something goes this bad, there comes a point where you have to scrap it and start fresh. The resin was mixed wrong, it didn't set, so there's essentially no core/skin bond. This hull is probably not safe to take out on the water.
     
  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You can take a coupon and make a delamination test.
     
  5. JR-Shine
    Joined: May 2004
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    JR-Shine SHINE

    Try testing it against a properly done panel as a control
     
  6. mobhaid
    Joined: Feb 2014
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    mobhaid Junior Member

    There exists the polyester resin and the polyester hardener and not well known is the accelerator chemical
    If you mix the accelerator chemical and the polyester hardener together first you risk to get an explosion from the high heat chemical mix .
    To reduce the risk of this type of accident it has been common practice since the 1980s era to only sell polyester with or without accelerator mixed in . The term is when purchasing polyester is to request slow set or fast set polyester .The slow set polyester is often hard to get will have little or no accelerator in it and is best suited for large molding such as large boat hull molding .Fast set polyester is the majority sold and suits small molding and repairs. The polyester will often set in to rubber state in about 30 minutes and hard set in few hours where its hard to cut off the rough edges and very hard after 24 hours .Many boat molders these days even use high speed polyester in molding hulls
    Some how i suspect you got polyester that has no accelerator pre mixed in often if the polyester is purple type color it often is rapid set polyester .If in dought ask the shop to sell you accelerator separately. In cold weather add more accelerator . Polyester shrinks 5% so many repairs will peel off due the shrink problem .Epoxy doesn't shrink .However there are times when epoxy is too soft and flexible compared to polyester so I have often done sandwich of the two materials .I might do thin layer of epoxy glass or carbon to be the sticky agent and then layers of polyester with some thin layers of epoxy in between .I find that reduces the risk of the repair peeling off and keeping the more rigid qualities of the polyester .The problem with epoxy is is unless the material is under pressure to squeeze out excess material in woven glass or carbon tows it tends to be too soft and then you have use lots more of it to get the needed strength.As a rough rule the slow set polyester risks to never set if the molding is small as there isn't enough heat made to set of the polyester .High level accelerated polyester isn't to critical to mix the hardener as slow set polyester .Unless you're doing some large molding i can think of no advantage to ever use slow set polyester .However the shops will try to sell it as its much cheaper .

    David
     
  7. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Good summary of problems.

    But I have a question about the statement

    "there are times when epoxy is too soft and flexible compared to polyester "

    That has to be a result of poor usage.


    eg.

    http://www.netcomposites.com/guide/strength-stiffness/13
    "After a cure period of seven days at room temperature it can be seen that a typical epoxy will have higher properties than a typical polyester and vinylester for both strength and stiffness."
     
  8. mobhaid
    Joined: Feb 2014
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    mobhaid Junior Member

    The problem with epoxy versus polyester is mostly for the amateurs and weekend boat fixers .If something will go wrong it more likely to be with epoxy than with Polyester .
    It often revolves around the fact that polyester will dry into a hard plastic pretty well every time as most modern kits are accelerated polyester often purple in color .Add some hardener and 20 minutes later chances are very high it will have set off and a few hour later the plastic will be rock solid . Even if they use unwoven mat glass strands for the job which uses on average 50% more polyester than woven mat does the job often works out with throwing lots of polyester at the problem .The people who often use polyester will often try the same stunt with epoxy and that is where the problem lies

    Epoxy resin is really more of glue than a ridged material .If you take some few grams of epoxy put it on the sheet of metal or plastic set it off after few hours you will peel of a piece of plastic that is not a ridged or as hard as polyester .Epoxy only really gets it rigidity when it it is combined with glass like woven glass and carbon fibers. The amateurs will often put extra layers of epoxy on top of the work much as they did with polyester giving the work a softer covering than polyester would and realistically not adding any strength.
    It the fact that epoxy resin will often not kick off when its cold and the fact that amateurs will throw too much epoxy at the problem that makes the epoxy soft .Professionals wont suffer these problems they will use woven mats and use pressure to squeeze out excesses epoxy and most important they remove excess epoxy and they make sure they work in hot conditions or suitable heat is there to kick the epoxy off

    David forever paddling against the wind in a rubber duck :D
     
  9. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    I challenge you to prove that strange statement. Lets see - does the chance of adding 2 or 3 extra drops of catalyst that cause premature poly hardening seem more likely than adding up to two extra cupfulls of part B of epoxy ruin the job ? i dont think so.

    That doesnt make sense to me at all. There is a lot more to getting successful jobs than the 'goo' setting. Its got to wet the fibre material totally, adhere to the substrate, and provide a fully waterproof solution. Epoxy gives even amateurs a much greater chance of that happening than Poly ever did.

    You really need to read more. After a weeks cure, especially if you use advanced curing techniques on epoxy - epoxy is a lot better than poly in all areas - see attachment.
    http://www.amtcomposites.co.za/site.../howto/Advantages of Epoxy over Polyester.pdf



    The resin of either sort does not give the strength - its the fibres. Adding extra layers of epoxy is not a structural thing - its a waterproof thing. Something Polyester cant do no matter how many layers you use.


    This makes little sense if you are arguing Poly V Epoxy. It takes proper engineering to create successful jobs in either material, and the fact that Poly seems to go harder, easier, more quickly is the very least of a builder problems.
     

    Attached Files:

  10. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member


    I have never seen a laminate peel off due to shrinking, I guess you could possibly make it happen, but is a non issue if the materials are used even close to the correct way.

    Alternating layers of epoxy and polyester sounds like a recipe for failure.

    There is no price difference between long and short gel time resins unless they only stock one style and need to special order a small amount of the other one.
     
  11. ondarvr
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    ondarvr Senior Member

    Now to the OP.

    The chance of the VE curing even close to correctly is almost non existent, although it may get hard the physical properties would be low.

    Like suggested, do a core sample so you can see for yourself how well it cured.
     

  12. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    I recently got an unpromoted pail of vinylester from the local supplier, so the OP is not alone in this. It had three stickers on the label and one on the top that stated that it had been promoted, however it took days to go off, in which time it took on a kind of dried up appearance, totally unacceptable, and it will have to be removed and redone.
    The supplier finally coughed up another pail, it works like it is supposed to, however he will not even talk about any compensation for the ruined work...
    He says it was a bad batch, but the batch number is the same, more likely poorly trained employees who botched adding/mixing the promoter.
     
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