Overhead void filling

Discussion in 'Boat Design' started by Jason Rodgers, Sep 21, 2022.

  1. Jason Rodgers
    Joined: Mar 2021
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    Location: Cruising

    Jason Rodgers Junior Member

    There are two overhead voids needing to be filled under the deck and directly beneath the bow cleats. These voids remained after prior deck repairs and need to be filled to create a level surface for the bow cleat backing plates to bear evenly on the underside of the deck.

    The voids are 10"L x 5"W and 1" to 1-1/2" deep.

    One idea floated was to progressively inject epoxy mixed with milled fibres from above deck through drill holes, using formwork under the deck to contain the required level, but this risks air bubbles being trapped at the primary bonding surface.

    Anyone filled overhead voids before with a better method?
     
  2. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    No.

    I'd just use a piece of really good hardwood, not teak or anything oily. Bed it in thickened resin. Then apply resin to the bottom edge to fill and probably some biax glass. Thickened resins will stick to hotcoat. So before adding thickened resins each time, paint the area with clear mixed epoxy and wait for it to gel before adding the thickened materials. I prefer fumed silica, never deeper than 3/8". If you really don't want a wood core; you can use coosa or corecell or marine foam of appropriate density. If the bow cleats are coming through here; the density cannot be less than say 24#, wood is best.

    Also, when you thicken resin, it has to stand in a pile for say 10 seconds or it'll sag out. I'd say about 2.2-1 by volume fumed silica to epoxy or so...

    All work from the bottom.

    If access is an issue; let me know.
     
    Jason Rodgers likes this.
  3. Jason Rodgers
    Joined: Mar 2021
    Posts: 10
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    Location: Cruising

    Jason Rodgers Junior Member

    Well all your advice makes perfect sense, especially as seen during my failed test runs. Much appreciated. I will use hardwood and over drill the timber to fill with thickened epoxy for the cleat bolt holes. .

    I did one test where I pushed up from below the thickened epoxy in place on a board covered in packaging tape. When I grinded the cured epoxy out I noticed a series of air bubbles all along the primary surface bond. I did not let the initial epoxy clear coat gel off before pushing up the thickened epoxy. I am getting lots of tiny air bubbles when mixing West systems resin and hardener.
     

  4. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Well, a wee bit of air entrainment is to be expected. It is kind of unavoidable. You can reduce it by making a thicker and thinner batch of thiickened resin. Just before putting up the board after it has been precoated and allowed to gel off; slather some thinner stuff on it like butter. The bottom side of the gunwhale should already have thickened resin butter into it. The thinner stuff will find the low areas.

    When you bed the board, make sure you precoat the wood on the bedding side and the edges. It will be sticky. You will want to wax or wrap those bolts in saran or take them out.

    keep plastic under the area and anticipate some mess; you may need to support the board for say 6 hours with a piece of wood

    the fillers and epoxy will shrink, so once the time has passed; you can do the filler under the board and a piece of glass..again, remember to precoat the wood with just epoxy

    wood likes to drysuck thickened resins, or rather dry wood has a tendency to pull resins into its open cells and leave the bond area of the thickened resins with less epoxy which can lead to joint failure..
     
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