For the 10,000th time... Polyester + plywood.

Discussion in 'Materials' started by AMCer, Sep 6, 2010.

  1. AMCer
    Joined: Sep 2010
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    AMCer New Member

    Okay, I need to replace the bunk/hull supports in a 70's North American. I have them cut (from marine ply) now I need to stick them in. I want to protect the lower few inches of the boards from soaking up water and rotting and I want to use polyester...

    What's the best way to get polyester to penetrate the wood and cure?

    (I'm only interested in polyester information, not epoxy.)
  2. gonzo
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    gonzo Senior Member

    The best way is to heat the wood to make sure most of the humidity is out. Also, the heat will thin the resin and make it penetrate more. Solvents are not good if you want water resistance.
  3. SamSam
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    SamSam Senior Member

    I read somewhere about the heat thing, where the wood is heated until the application starts and then stopped, so the wood as it cools draws the resin in.
  4. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Buy an infusion resin, it will have a very low viscosity to start with.
  5. tunnels

    tunnels Previous Member

    Simple dont use it !!!!But If you insist thin the resin 10% with STYRENE ,add cobalt to speed up the Gel/cure time .
    Remember it will only penetrate to the glue line so if you have a 7 ply the veneers are thin so wont go far !!. less plys thicker wood veneers so the further it will soak and penetrate . Let the first coat gel! Light sand and apply a second coat with some Parraphin wax to get rid of the sticky surface . :)
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Polyester will not water proof your plywood piece ends. It will make it water resistant, but not water proof, which is likely the key to the failures you saw, that required this repair. The only success you can hope for is film thickness, staving off moisture ingress before evaporation. This is what the manufactures bet on and it doesn't work in the long run, but they can make money off it in the short term.
  7. darr
    Joined: Nov 2004
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    darr Open Minded

    Oh My, Don't do it!

    Your boat will immediately sink, even if you are blocked up on the hard, you will come back the next day and the boat will be sunk below the ground level.

    Polyester will cause immediate catastrophic failure of all key components in the hull, the stern tube will immediately jump out of the hull, because you dared to put Polyester on it.

    The engine in horror and shame will immediately self destruct.

    Your mast(s) will jump off the hull so fast and with so much energy that they will be tracked into orbit.


    Relax, just having a little fun.

    Follow the advice of the cooler heads and bring the temp of the bulkheads up above ambient as far as you can safely go. Apply the resin, let it soak, after a couple of minutes, but before it gels, put on a second coat. Let the wood cool. After those coats are set, sand lightly, third coat.

    I do agree that it won't make it waterproof, but it sounds like the first attempt from the factory lasted 30+ years, so you should get 30++ from them this time around.
  8. apex1

    apex1 Guest

    These senseless attempts to save a penny at the wrong end of the task seem to be indestructable.

    Give me the best recipe to make apple pie, but leave the proven ingredients out! In particular apples.

    Every month again..........
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Come on Richard, you didn't consider marrying the pretty little thing with the brain of a 10 year old?
  10. troy2000
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    troy2000 Senior Member

    I used to have a friend in his fifties, whose third wife was seventeen years old. He told me, "the older I get, the younger and dumber I like them.":p
  11. apex1

    apex1 Guest

    Well, must confess, I did convince her about the need of daily measuring her core temperature in a very natural manner.
    But I did not consider marriage.:)


    my last was 30 years younger than me. But well educated and very intelligent. We had very, very interesting disputes, but never squarrel or conflicts. And never ever one harsh word. (she may rest in peace)

    I do not like them dumb. The dumber they are the better they nag, not sh@g.

  12. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Here's another way to look at the epoxy/polyester issue. OK, bondo (you know, the body filler used on cars) is based on polyester. Over the years before I started playing around in boats I used it to touch up my cars. It NEVER held up for more than one winter. Now I use use boat building epoxy and fiberglass/fillers on the cars when I want to repair a rust spot. THESE repairs, done with epoxy, last.

    So for the 10,001 time no polyester, no, no, no. Can't afford epoxy? Then get a second job and wait until you save enough to do the job right.

    BTW, Troy, you need a new friend:D

  13. gonzo
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    gonzo Senior Member

    It is hard to keep epoxy information off a thread when you say polyester ;)
  14. apex1

    apex1 Guest

    ....and vice versa..........:cool:

  15. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    The best way to seal wood would be to vacuum the wood in the heated EPOXY to suck all air out and then pressurise it, ie in a chamber to force epoxy in.

    Do not, I repeat :D, do not use polyester on wood, it works very poorly, and you will have to do it over again soon.

    Maybe Jeff can make it a big sticky on the forum.

    If you're hell bent on using polyester then use something other than wood. And off late I do not glass polyester to polyester parts I glue them. It makes a better bond and does not delaminate.

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