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  1. #1
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    To vacuum bag, or not? That is the question.

    Hey guys, I'm getting closer to the point on being ready to start laying new glass in my Viking (I have a build thread posted here). I've decided to go with a balsa core based on the strength characteristics.

    My question is, should I vacuum bag the core in or not?

    When I reach the point of laying glass its going to go, repair holes with a few layers of 1.5oz CSM, layer of 1708 over repairs, full layer of 1708 over entire bottom, 1.5oz CSM, 1/2" balsa core, 1708, etc. (Was told it's going to be over built) Oh well, I want it to last.

    Jim Swanson from Express Composites said I shouldn't need to bag the core, just do an extra wet layup of the CSM and lay the core into it. Not that I don't trust Jim, I would feel a little more comfortable if I bag it in. I'm a beginner here and want it done right the first time.

    What is your input?

    I do have access to vacuum pump if I go that route, I'll just need the starter kit with the film. fittings, etc. I'm not worried about the cost of a kit, I want the best boat possible when finished.

    Thanks in advance for your input, Tony.

  2. #2
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    What resin are you using? And what kind of vacuum pump will you be using?

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  4. #3
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    I used west systems and their venturi pump they sell. Did the core in sections but wasn't that bad at all once you figure out what the hell you are doing. I got some aluminum pucks for the guage and vacuum connection. I put down 12 oz and wet the hell out of the balsa and put it under vac and its stong as hell. 1708 over the top of the balsa and good to go

    1973 Viper w/ V4 Crossflow.
    1978 Viking w/ 1978 175hp Merc, My first restoration in progress

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  6. #4
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    You need to lay more glass on your repair areas as you will have to also do those spots from the outside. I taped the repair spots with some good duct tape from the outside. Installed the core, bagged it. Now finish the inside and then repair the outside of the hull and prep for finish

    1973 Viper w/ V4 Crossflow.
    1978 Viking w/ 1978 175hp Merc, My first restoration in progress

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  8. #5
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    I dont think you need all that glass under the balsa, strength is needed on the inside of the boat to take the waves and whatnot. I did 12 oz of glass, maybe I should have done more, the pros will be here soon to tell us.

    1973 Viper w/ V4 Crossflow.
    1978 Viking w/ 1978 175hp Merc, My first restoration in progress

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  10. #6
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    Quote Originally Posted by outasite View Post
    What resin are you using? And what kind of vacuum pump will you be using?
    Polyester I believe. Told the guy at the composite shop what I was doing and this is what he set me up with.

    The pump I have access to is used for AC work in HVAC systems. Its an electric pump. I kinda figured vacuum is vacuum.

    I apologize for all the newbie questions.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  11. #7
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    That will work just fine, its General Purpose Poly resin that the boat was originally made with. Your issue will be doing all the work of the layup. Getting the glass wet and in place, getting the balsa pre wetted, getting it all under your peal ply, breather, the bag it self (envelope), and getting the core under a vacuum quick enough before the resin starts to kick. Is vacuum bagging really needed, NO. But it does work very well and makes a very strong, and lighter part as the breather will suck up extra resin off the top of the part (balsa).

    1973 Viper w/ V4 Crossflow.
    1978 Viking w/ 1978 175hp Merc, My first restoration in progress

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  13. #8
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    IMO poly or vinyl are both to fast setting for a first time bagger. It will start to gel in around twenty minutes,You'll have to haul ass to get it done.Most use epoxy when bagging,witch brings me to why I ask about a pump.Most HVAC AC pumps will overheat when left running for hours at a time.(for epoxy).Nothing wrong with a good old hand layup,use a good bedding compound and do a section you can handle.Weight it down I am using roofing shingles layed on bakers parchment paper.Others use bricks,batteries,propane tanks and any number of other things.

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  15. #9
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    Hmm I'd like to bag mine up too but dang it, Im worried my newbness will catch me short on cure time and end up in a mess. I will watch and see how you make out. Use the force
    1988 Hydrostream Valero V, 2.0L Mariner
    1985 Beretta, Evinrude 115 crossflow

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  17. #10
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    Quote Originally Posted by rjdubiel View Post
    Your issue will be doing all the work of the layup. Getting the glass wet and in place, getting the balsa pre wetted, getting it all under your peal ply, breather, the bag it self (envelope), and getting the core under a vacuum quick enough before the resin starts to kick. Is vacuum bagging really needed, NO. But it does work very well and makes a very strong, and lighter part as the breather will suck up extra resin off the top of the part (balsa).
    Wet Bagging something that big is not for newbies.

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  19. #11
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    Quote Originally Posted by outasite View Post
    IMO poly or vinyl are both to fast setting for a first time bagger. It will start to gel in around twenty minutes,You'll have to haul ass to get it done.Most use epoxy when bagging,witch brings me to why I ask about a pump.Most HVAC AC pumps will overheat when left running for hours at a time.(for epoxy).Nothing wrong with a good old hand layup,use a good bedding compound and do a section you can handle.
    Sounds like the voice of experience.

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  21. #12
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    Your primary goal when bonding a core, is zero voids between the outer skin and the core. The core is light weight so it needs to be held down, so that it conforms to the laminate, while the resin or core adhesive gels. If you want to bond it on to the wet laminate, you can hold it down with vacuum, or a LOT of weight spread EVENLY over the WHOLE panel. This is even the case for flat panels. You can get away with using weight if the mould is substantial ( it wont deform under the extra weight ) especially if you use a caul plate. If the laminate isn't in the mould - i.e. you are rebuilding the hull, then the then the thin outer skin will deform if you put enough weight in it to make sure you haven't got any voids. So your other option is too use a core adhesive. The core adhesive is designed specifically to a give void free bond. It is a sticky paste. If you put enough down on the laminate and push the core into it with your hands it won't move when you take your hand away. I have bonded a lot of cores. In the god ole days we used lots of core adhesive and it works! The moral of this story is .... I would NEVER sit a core on wet glass, without adequate clamping pressure, when my life depended on the quality of the bond. And in this situation I can't see how you could get adequate clamping pressure, using weight, without distorting the shape of the hull.

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  23. #13
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    When doing a hand layup just remember the core wants to flote. To little weight and you get a resin rich bond that will crack, and add unnecessary weight.Put to much weight and you will push to much resin out and have a dry bond with no strength.And possibly deform the hull.None of the hydro stream hulls were bagged when new,but they were also all built in a mold!

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  25. #14
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    Nice thing is he has the boat in a very supportive cradle. I would go the pad core up to where the stringers will stop. Then install the stringers. Now the core on the outside of the stringers will not slide when installing, the core and whatever weight is on it will basically rest against the stringer. I bagged mine all before the stringers were installed but the vacuum kept the core where I needed it. Either way, work in small sections at first, like a 4 foot area, then once you know the gel time you can work into bigger sections. If ya need help let me know, helps having a mixer and another person to roll and do othere things

    1973 Viper w/ V4 Crossflow.
    1978 Viking w/ 1978 175hp Merc, My first restoration in progress

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  27. #15
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    Quote Originally Posted by GregAdams View Post
    Wet Bagging something that big is not for newbies.
    Yep, I did small sections on the one side, then did the whole under bow in one section. You can see the 4 foot spacing on the left of the hull
    Click image for larger version. 

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    1973 Viper w/ V4 Crossflow.
    1978 Viking w/ 1978 175hp Merc, My first restoration in progress

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