General Infusion Strategies

Discussion in 'Fiberglass and Composite Boat Building' started by weldandglass, Apr 17, 2017.

  1. weldandglass
    Joined: May 2010
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    weldandglass Junior Member

    Per my other post about IMC’s, I’m about to start an 18ft skiff built from a mold of my design utilizing cored laminate and epoxy resin. The last skiff I built was a one off and everything was bagged. I’d like to move onto resin infusion but I’d also like to mitigate the risk of failure on any large, infused pieces.

    I’ve studied enough of other people’s infusion projects to understand the general process. However, I have questions about infusion particulars, especially when infusing a mold and trying to keep weight to an absolute minimum. Weight is a primary concern on this build and if I were to bag it I would have to bag the outer skin into the mold, let cure, bag the core with bonding putty in place, let cure, then bag the inner skin in place.

    First, the core bonding putty adds quite a bit of weight and so I’d like to avoid this. However, it seems like the highest potential for failure would occur if I try to infuse the entire core-laminate stack in one shot. If I don’t, however, I assume I’m back to bagging the core in place with bonding putty regardless of whether I bag or infuse. Is there a method that would provide less resulting weight (i.e., some way to avoid infusing an entire core-laminate stack at one that would also alleviate bonding the core with putty to the outer laminate)?

    Second, if I pursue trying to infuse the core-laminate stack in one shot in the mold, it’s my understanding that I need to use a perforated foam with perforations every 1-2 inches. Flow media of some kind would be necessary to transfer resin across the visible laminate surface and the perforations would transfer resin to the underside (mold-side) laminate surface. It’s my understanding that the scored core isn’t necessary for successful infusion and that it’s only necessary to get the core to conform to curvature in the mold and that these scored channels add significant weight to the core due to resin uptake. Do I have all of this right or are other options available? My assumption is that if one were trying to minimize weight they would use perforated, non-scored core in the flat areas of the mold and scored, scrim-backed core in the curved areas. However, I’m guessing that these materials would infuse very differently and this would render this strategy infeasible.

    I have more questions that I will ask under this thread but any preliminary advice is much appreciated.
  2. abourgault
    Joined: Jul 2014
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    abourgault Junior Member

    You can heat the core to make it conform to the curvature. If the core is of the plastic kind.
  3. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    I've only done small flat pieces and I'm no expert on infusion, scouring the core say 1mm X1mm every sq/in rely helped the resin flow so much that there was no need for flow media which pending on what your using can eat up a lot of resin which you just end up throwing away.
  4. weldandglass
    Joined: May 2010
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    Location: Gulf Coast of Texas

    weldandglass Junior Member

    So, after looking around I've seen that Proset epoxies have an "extended open time" laminating resin that is supposed to give you 8 to 9 hours working time at 85 degrees F.

    This should be enough time to hand-laminate the pre-cut outer skins with directional glass, install the pre-cut core pieces into place, and bag the outer skin laminate and core all at once.

    I would utilize non-scored core in the flat parts of the mold and scored core in the curved parts.

    If I use a resin rich 1.5 oz mat layer as the inner ply within the outer laminate skin, I'm thinking this will provide enough resin for bonding the core and filling the scores in the core.

    I can then infuse the flat parts such as bulkheads and stringers and tab them into the hull.

    Does anyone see any problem with this plan?
  5. AusShipwright
    Joined: Aug 2016
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    AusShipwright Junior Member

    Having done a few infusions and some vacuum bagging, it does sound a bit complicated. All that hand laminating sounds counter-productive when at first you mention the need to save weight. How come you don't want to infuse all at once?
  6. weldandglass
    Joined: May 2010
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    Location: Gulf Coast of Texas

    weldandglass Junior Member

    As stated previously, I'm working under the assumption that the use of grid-scored core is inescapable in the curved parts of the mold. I want to use as little grid-scored core as possible to minimize resin uptake by the core and resulting weight the finished panels. I know it's been suggested that plain, flat core could be heated to make it conform to the curvature of the mold but this doesn't sound ideal.

    For now, I'm stuck on the idea that bagging the outer laminate and core in one shot and only using scored core in the curved parts of the mold will result in the lightest weight finished panels. I would readily welcome any detailed advice to the contrary.
  7. groper
    Joined: Jun 2011
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    groper Senior Member

    You can infuse the whole thing in 1 shot. However you should have experience before trying it.

    How much curve is there ? Got any pics?
    It's normal practice to use "double cut" foam for for infusing curved areas in molds. Don't use scrim backed contour foam - too much resin uptake and tends to print bad too. Double cut foam works nicely.

    Once your out of the curved area, go back to infusion perforated only foam with a resin flow media over the whole lot.... Double cut (knife cuts not scored) foam acts as a transfer media itself and will add a little weight but it's minimal unless the curvature is extreme which will open up the cuts and hold more resin in the resulting void of each cut.

    Regarding mitigating risk , you probably should simply practice on flat panels and cut your bulkheads from them. Once you've got it down, move onto your full hull infusion. You'll know when your ready... And ask lots of questions and put up pics when your ready as you'll get plenty of help here before pulling the trigger ...

  8. rob denney
    Joined: Feb 2005
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    rob denney Senior Member

    What Groper said, particularly re experience and practice. An alternative to double cut foam is to use strips in the curved areas. If the curves are not extreme, it will be lighter to put the cuts in the core on the inside of the curve, not the outside. Whatever you do, for minimum weight there must be as few (ie none) gaps in the core as possible. The best way to ensure this is a lip around the mould that forces the foam tightly into position against the glass and mould. Care at this stage will pay big dividends when you weigh it.

    Resin rich mat would add a lot of weight for no gain.
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