Resin thickness contribution

Discussion in 'Materials' started by dmend, Sep 13, 2016.

  1. dmend
    Joined: Sep 2016
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    dmend New Member

    Hello, This is my first post to your forum and although I'm not building a boat your forum looks to have very experienced fiberglass users. I am replacing a wood engine cover that is 11.5mm thick. I can find info on ounces of resin to apply to the fiberglass sheeting, but nothing on how it contributes to the thickness. Based on the table below, with 9.67mm of fiberglass sheets (no resin)what can I expect the resin contribution to the thickness be?

    layers fabric thickness net thickness
    2 coremat 4 8mm
    1 1708 Biaxial 0.044 0.044mm
    2 1-1/2 oz CSM 0.045 0.09mm
    2 18 oz Woven Roven 0.635 1.27mm
    1 10 oz e-glass 0.0154 0.0154mm
    1 Surfacing veil 0.254 0.254mm
    Total Fabric Thickness 9.6734mm
    less Target thickness 11.5mm
    Net difference/resin contribution 1.8266mm

    Thank you,
  2. groper
    Joined: Jun 2011
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    groper Senior Member

    some of your numbers dont look right to me - 1 layer of 1708 = 0.044mm???? 10oz e-glass 0.0154mm????

    As a guide, finished laminate thickness of hand layed e-glass and resin is approx 1mm per 30oz. Thinner if vacuum bagged or infused...

    To wet it out youll use approx the same weight in resin, as the glass matt your impregnating.
    so if you have a glass matt that is 30oz/ft, and you have 1sqft area, then youll need 30oz resin to wet it out... 10sqft area youll mix up 300oz and so on...
  3. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Most 'normal' layups aim at around 40% maybe 45% (for hand layup) resin to fabric. As Groper says, those thicknesses certainly look on the 'thin' side! Maybe a decimal point issue?

    Why not test a small bit of fabric layup? Including a built up bit with core, then you can have pretty good confidence. It's pretty quick too with polyester. I'd concur that a hand layup will be thicker than a vacuum bagged or compressed layup, but not by an enormous margin if reasonably done.
  4. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    The choppy will be significantly thirstier(x 2-2.5) than the stitched & woven.... & the laminate bulker/coremat/upica very resin hungry at from memory around .65kg per mmthickness x M2 with laying into chop & overlaying with chop required.
    I'd question the target thickness as needing to be equal to the timber it's replacing, maybe very heavy in a replacement sense over the timber.
    I think the decimals moved also in some cases
    No indication of gelcoat or flowcoat use also which adds some 1mm or so .65/.45
    6ozchop(1800gm) used to equal approx 1/8"(3.2mm) laid up back whenever depending on consolidation.. tight or juicey!!
  5. dmend
    Joined: Sep 2016
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    dmend New Member

    Thank you for your comments.
    I sure made a mess of those numbers. I mixed up decimals and millimeters on my spreadsheet. I got it straightened out. I am trying attaching a spreadsheet with the new numbers instead of copying the numbers which won't hold formatting in the post. I got my thickness down to just over 1/4 inch and if my resin thickness calculation is off there is plenty of room for error at this thickness.

    Lay-up plan: surface veil, csm, coremat, csm, woven roven, surface veil, gelcoat

    I plan on using a polyester resin without wax and for the final layer on the surface veil I'll add wax to the resin, then after trimming and drilling for hardware attachment I'll apply the gelcoat.

    Question: Using a no-wax resin and applying the final layer with waxed resin to seal the resin so it hardens, will the first layer which is un-waxed resin harden up because there is no air in contact with it, or after removing it from the buck do I need to apply a layer of waxed resin on the inside to seal the inside?


    Attached Files:

  6. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    I've never needed to use a waxed resin to then bond gelcoat to. It will cure hard anyway, without the wax. You only need wax in the gelcoat. Ideally you would apply the gelcoat (with wax) onto a still slightly tacky resin. This will give a chemical bond.

    If you use wax in the resin you will need to let it cure and abrade every part of the surface and ensure it is whistle clean prior to applying the gelcoat. Why make this extra work, is it going to be really rough? It (polyester resin) will still cure hard without the wax.

    Think of how you make a mould off a plug, which is the reverse of what you are doing. The gelcoat would have no wax, then laminate (cloth, csm, whatever) then maybe a sealing coat of resin with no wax. This will cure hard and dry. You are doing the opposite and require wax in the final gelcoat to seal the surface. I assume the last layer of your layup is open to air, ie gelcoat.
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