laminating overhead

Discussion in 'Fiberglass and Composite Boat Building' started by nevilleh, Jan 2, 2009.

  1. nevilleh
    Joined: Sep 2008
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    Location: scotland

    nevilleh Junior Member

    Hopefully a simple question to answer :

    Is vacuum bagging a suitable method to aid core fitting & laminating in the overhead position . . i.e. upside down ?

    Never done it upside down before !

    Thanks in advance !


    Neville
     
  2. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Hi Neville,

    This sounds like it'll be a tricky job to do. And yes, I would say that if you want the core to actually bond to the fibreglass under these conditions, vacuum bagging is essential.

    But I don't think bagging alone will do it.... you'll need a suitable resin (something that doesn't flow too much, but can still soak into the fibreglass), for one thing. If your shapes are all convex, you might be able to stretch the cloth around the mould and secure it at the top.... or you might have to use little staples all over the place. Everything's going to want to come down on top of you the first chance it gets. Keep the resin usage to a minimum (high fibre/resin ratio) and the structural fabric might have a chance of not being pulled off by the weight of the resin.

    Perhaps some folks who have tried this can offer some tips?
     
  3. nevilleh
    Joined: Sep 2008
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    nevilleh Junior Member

    The project is actually a new cabin top. Most of it had the core applied the correct way up, but a little got missed and now its on the boat.

    There is also quite alot of core to bond on vertically , approx 6 feet long x 2 feet high. (cabin sides).

    I am thinking that vacuum bagging should work ok if I let it start to cure before letting the vacuum off.

    Maybe there will be some people who have done this before .

    I dont want a mess & a disaster on our hands !


    Neville
     
  4. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    You'll want to maintain full vacuum until it's cured to a solid state. That pressure is essential to get the core and skin to stay in contact throughout the curing process. No point in risking the integrity of the whole job so you can free up the pump a few hours earlier.

    Laminating vertically isn't too bad. If you don't mind the hassle of bagging, it really does take a lot of the risk out of the equation.

    For the overhead part, you might try trowelling a resin thickened with filler (colloidal silica, perhaps) into the surface of the exposed core foam, and stapling the cloth layers to the foam as you work them into place.

    Personally, I prefer to work with the surface the other way around..... no chance you can capsize the boat for a few hours while you do this? ;)
     
  5. nevilleh
    Joined: Sep 2008
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    nevilleh Junior Member

    Yes , i suppose the biggest problem will be assembling it all upside down and securing it before it is held by the pump. I had not thought of using staples !

    I was going to use a thixotropic additive. It is plain old polyester resin and csm on top of a 1/2" PU core.

    Neville
     
  6. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    If you are allready prepared for vacuum bagging why not take the obvious step and do with vacuum infusion.. neatest way..
     
  7. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    true, and the foam and cloths are glued on anyhow during the process
     
  8. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Indeed you can spray-glue the laminate stack to the cabin top, then infuse. When using staples, consider "Raptor Composite Nails and Staples" which are plastic, not metal.

    When wet bagging, use a thicker resin, or even use aerosil to thicken the resin. Also consider pre-wetting the fabric outside the boat, on a (covered) workbench. And get someone to help... Roll the fabric onto a spare cardboard tube, and unroll on the ceiling. (with 2 people).
     

  9. buckknekkid
    Joined: Oct 2005
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    Location: north of pompano

    buckknekkid Senior Member

    Ive done it

    Old trick, Lay up on wax paper on a door skin. You can use drywall poles sold in the big box stores to hold it in place until it cures.. Not very scientific but it works. I can post pics later.
     
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