wet, not rotten deck core

Discussion in 'Fiberglass and Composite Boat Building' started by RonHH, Nov 17, 2011.

  1. RonHH
    Joined: Nov 2011
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    Location: Birch Bay

    RonHH New Member

    I have a 1979 CheoyLee Trawler and the teak on the side decks and bow was unsalvageable. I removed it, drilled out all the hundreds of screw holes and cleaned off all the black tar. the wood core between the top and bottom layer of fiberglass is wet from the leaking screws. The wood core is not rotten in any of the screw holes. I even took a hole saw and cut out a 1 1/2 inch peace of the core and it is very hard but just wet. The core is not laminated plywood, It looks like a peace of chocolate fudge. Is this Balsa or what? It seems like a waste to remove all this good wood just because its wet. I want to fill in all the drilled out screw holes with epoxy and put down a nonskid finish. What is the best way to dry out this wood core or what are my options? Thanks
  2. rasorinc
    Joined: Nov 2007
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    Location: OREGON

    rasorinc Senior Member

    Consider putting 2-4 box fans 2' x2' in the hold blowing upward to take the moisture out of the boat not blowing it into the hold. LEAVE THEM ON FOR A FEW DAYS. If the wood then feels dryer put a soft cover over the surface with some old blankets over the cover and put a series of 100 watt to 200 watt light bulbs in the boat under the wet boards--heat rises-- leave them on a few days and then take a moisture reading guage and check it all out. You will probably spend $100.00 in electrical usage. Cheapist way I know to dry things out.
    2 people like this.
  3. pauloman
    Joined: Jun 2010
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    Location: New Hampshire

    pauloman Epoxy Vendor

    after drying out the core the common fix (not the best) is to inject a solvent free epoxy that will bond to wet or damp surfaces....

    progressive epoxy polymers
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I've seen plenty of wet balsa and never have I seen it dried sufficiently, without a lot of time (months) or an autoclave or other way over the top, for the average person system. If it's dark in color, you may not feel rot, but it's on it's way.

    You can wait months with heaters, blowers and some praying it'll dry, or you can rip out the soaked balsa and install a new core (which doesn't have to be balsa). I know this sounds harsh, but if you investigate a little further, you'll likely find the core that seems solid, actually just has a solid skin over it, but underneath this skin, it's going to mush.

    The simple check is to physically remove a square foot of core, all in one piece if possible, then chop it into 1/2" (or so) slices on a table saw or miter saw. You'll very likely see the core is soaked, the plastic skin is keeping the moisture inside the core material and this material is rotting (use you nose, it's generally obvious). If on the other hand, if you find the core is solid wood all the way through your sample, then you can hope it'll eventually dry out and you can spend a few weeks with a syringe, some goo and having fun offering insulin shots to diabetic fastener holes.
  5. CatBuilder

    CatBuilder Previous Member

    What PAR said. :)
    1 person likes this.
  6. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    Of the core is wood then it's probably rotting somewhere, you just gotta find it... Is it worth putting all the time and money on new teak knowing the core could be rotten somewhere and could give out some day, I'd find that hard to live with personally...

    But if your convinced the core is ok and you want to dry it out, consider this;
    Strip off the top layer of glass If possible orherwise put rip cuts 50% depth at 2" Spacing or similar, try going in a line betwenn all the old screw holes etc with a circular saw- this will later be filled with bog and reglassed over the affected area.
    Apply a layer of breather material like shade cloth or vacuum bag blanket etc then vacuum bag plastic over the entire area, sealed around the edge of affected area.
    Pull an absolute vacuum with a decent vacuum pump and make sure you get at least 28" vacuum, leave this for several days including a small heater below the affected area. The water boils off and is removed by the vacuum pump , (water will boil at room temp in a strong vacuum, the heater speeds the process faster again)
    After several days, check the moisture and you should be good to bog And reglass the deck...
  7. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    Black is not good. Did all the test holes drilled show black? The core should be replaced, I'm afraid. This is asuming it is balsa, which you identify as being end grain, meaning balsa alone of all cores has the grain oriented up and down.
    It's a lot of work but at least you won't have put a large amount of work/time into drying out the original core. Using epoxy to bed the new core you will actually improve on th original construction, which used polyester resin and which now allows lateral migration of water ingress, which epoxy can prevent.
  8. MJT
    Joined: Jul 2012
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    Location: North Kingstown, RI

    MJT Junior Member

    I'm replacing the core on my Cheoy Lee Offshore 40. The core is thoroughly wet and I'm cutting up the deck in sections, removing the core, cleaning up the laminates, replacing the core, then fairing the deck. It's a big, but once-in-a-lifetime, job.

  9. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    The following I've never tried myself because my boat doesn't have wet core materials, but it should work:

    Seal any screw holes where water may have seeped in with a marine sealant. Drill a hole in the center of the wet area and install a Schrader valve there (similar to the thing a car tire has, but with a threaded end.
    Connect the valve to a vacuum pump designed for evacuating air conditioners (I bought mine through Ebay for $120). The pump will pull high vacuum and whatever moisture there is will boil out at room temperature. That may take several hours or even days, depending on the surface area and the amount of water under it.
    When the sound of the pump has changed and no more damp air comes out, prepare a small amount of epoxy or polyester resin, close the ball valve, remove the vacuum hose from the pump, dip the end in the resin and open the ball valve again. The vacuum will pull the resin to where the laminate separated from the core.
    Remove and flush the vacuum hose with acetone if you wish to reuse it, discard it if not. Wait with the removal of the Schrader valve until the resin has cured.

    I use the same vacuum pump for drying mushrooms and figs, it is slow but very effective.

  10. the1much
    Joined: Jul 2007
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    Location: maine

    the1much hippie dreams

    my 1 cents worth is this. i had old old builder tell me that if we come across any core that has been we replace it.if you dont get totally dry before glassing over it will ALWAYS cause damage down the road.to this day the things he told me has never been wrong.
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