Bedding Foam Core to Outer Skin

Discussion in 'Fiberglass and Composite Boat Building' started by weldandglass, Feb 5, 2012.

  1. weldandglass
    Joined: May 2010
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    Location: Gulf Coast of Texas

    weldandglass Junior Member

    I'm building a 17-ft boat out of divinycell/biaxial glass/epoxy. The hull is close to finished and was built off a wooden jib. For construction of the deck, however, I've built a temporary mold. I've laminated lots of divinycell but never in a mold and I've got some questions about bonding the core the outer laminate.

    I know that divinycell has some bedding compound for use with their cores, should I use this or can I use an epoxy/filler slurry? Is vacuum bagging absolutely necessary or can a good foam/laminate bond be achieved without bagging? I've vacuum bagged almost all my laminates tot his point but my deck mold has a bunch of sharp, raised edges which would make bagging difficult.

    Any and all advice would be appreciated.

    Thanks.
     
  2. CatBuilder

    CatBuilder Previous Member


    Any sharp edges should always be ground into rounded corners when glassing - especially hand laminating. That way, you get better adhesion. The glass will tend to lift off the surface if you have sharp, raised edges.

    So you used a true female mold for the deck, then laid up the outer skin of the deck in that mold (after mold release) and now are getting ready to stick the Divinycell core in?

    If so, thickened epoxy is fine - better even, but you really should bag this, most importantly of all.

    Getting core to stick to the inside of a female mold layup is probably one of the most difficult things to do. Bagging the core down to the airtight glass layup you have already done will ensure a much better bond. It would be quite iffy doing that bond by just laying the foam in there.

    Worst case, can you at least keep your core 1" off the edges and tape your bag down to the 1" glass border to get a seal, filling in the extra 1" strip later with clamps?
     
  3. weldandglass
    Joined: May 2010
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    Location: Gulf Coast of Texas

    weldandglass Junior Member

    The sharp edges are not in the mold. All transitions within the mold have been properly radiused using molding clay. This is a temporary deck mold, the outer portion of which was made by securing a 3" strip of HDPE to a my 20-ft 8-ft work table. This strip forms the down-turned sheer line of the deck. I used wooden blocks and screws to secure the strip to the table. The blocks are on the exterior of the mold (i.e., not within the mold surface) but the bag would have to fit over them if I were to bag the core.

    I appreciate the advice on bagging. I figured it would be very difficult to properly bed the core without bagging but wanted to be sure no one had any other recommendations.
     
  4. weldandglass
    Joined: May 2010
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    Location: Gulf Coast of Texas

    weldandglass Junior Member

    After thinking about it a little more, I can probably just drape strips of old towels or something over the wooden blocks so they don't puncutre the bag when I pull vaccuum.
     
  5. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    to do this correctly, you need to make sure there is no air trapped between the laminate and the core and that there is adquate bond of core to laminate - This is very important. The only sure fire way to do this, is to use vacuum and a perforated core material with excess resin mixture to allow trapped air to escape and the excess thickened resin to squeeze out/come thru. Details on the process are outlined in here;

    http://www.diabgroup.com/americas/u_literature/u_pdf_files/u_bul_pdf/Divil_TB.pdf

    Divilette is just a thickened PE resin, you can use your own resin mixture in the same way, just follow the step by step application guide.
     
  6. tunnels

    tunnels Previous Member

    Post some pictures of what ya got !!. Its a power boat ? what kinda speed you looking at ?
    Lets see some pictures
    True core bond is not only thickened but has a special formulation to make it stick and is semi flexable
    Just sucking epoxy into resin is not a good choice and to many things can and will go wrong !! any kind of slurry mix need to be able to hang on a angled surface at the correct thickness before you places the pre resin primed foam down . All the foam needs to be prefirated and have shanffered ground edges before you lay it in the boat !!:)

    Lots a Pictures please !!
     
  7. weldandglass
    Joined: May 2010
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    Location: Gulf Coast of Texas

    weldandglass Junior Member

    Groper:
    Thanks for the link. I had seen that publication from DIAB some time ago and had forgotten about it. That pretty much tells me everything I needed to know.

    Tunnels:
    It's an outboard powered boat but it won't be very fast as low horsepower and shallow draft are the objectives. I'll try and post some pictures after I get the hull and deck put together.
     
  8. CatBuilder

    CatBuilder Previous Member

    Any way you go, you really do have to bag foam onto glass. You can hand laminate glass onto a foam surface, but going the other way around requires bagging.

    The perforated foam is a good idea too, but I'm guessing you don't have that.

    If you really want to turn your Divinycell in to perforated, you can alway impale it on a board with a lot of nails in it. That's what people do in a pinch.
     
  9. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    Ive made my own 2mm grooves in core material with a circular saw to do the same job, this way the air and excess resin gets sucked out to the edges of the job rather than up thru the core. However, this is only effective on long/narrow jobs as otherwise, its just too far for the air/resin to travel and you will not suck it all out...
     

  10. tunnels

    tunnels Previous Member

    When is max vac not required ??

    Buy perfirated core ,simple !! if its not got holes to let the air and the surplus resin and core bonding out from under you are asking for trouble , believe me ! You can pull vacumn as hard as you like it could have huge voids under the core !!. Been there seen it all happen before and was done by experts , shook there heads in disbelief and could not believe what had happened !! Voids as big as dinner plates and lots others ranging in size down to as big as your little fingernail !!. And yes the vac was as high as possible to get !! And That was the problem so was discovered in the end !!

    SO I ASKED THE QUESTION "HOW MUCH VAC DO YOU ACTUALLY NEED TO PULL A CORE DOWN to make a perfect job "????? The answer my suprise many people !!:eek:

    If you use a cordless drill make sure the swarf from the drill does not block the holes !!
    If you are using core bond the swarf will not allow the core bond to come up to the surface or even the resin within the corebond ,It also slows the resin as well and in somecases can totally reblock the hole . We find it better to use a ice pick and push it through and made a perfect hole totally clear and clean . Lay the sheets on 50mm thick polystyrene and push all way through so the wee piece wont break out the underside !!

    I know "Catbuilder" is going to have a field day with what i have just written !!
     
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