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Thread: how thick will two layers of fibreglass cloth be?

  1. #1
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    how thick will two layers of fibreglass cloth be?

    Hi all,

    I don't do a lot of working with fibreglass but I have a small project coming up that I have a question about which I was hoping someone could answer.

    The body on my truck is made with a steel frame, onto which plywood siding is glued, and the edges and corners protected with aluminium capping. The siding is made of 18mm plywood with a thin layer of GRP (fibreglass) laminated onto either side. On the back corner, water has got under the aluminium capping and has rotted a section of the siding behind the GRP.

    It is unnecessary and too much work to replace the whole panel, and so I plan to cut out and replace the rotten section, about 500 mm x 250 mm. Below is my rough plan of action, using a simple half lap joint and an overlapping layer of fibreglass.



    I could buy a small piece of the same laminated plywood, but getting the join to be seamless will be awkward, and I think that my plan is stronger as the fibreglass will tie the new to the old properly.

    My question regards how deep I should leave the rebate to glass up to. I have some 280g twill weave and some heavy 600g biaxial cloth, I plan to use one layer of each. If I rebate too far, I am happy to fill up to the level of the old plywood with resin and filler, but it would be a waste of material and would take longer to fair. If the fibreglass ends up being proud Iíll have to sand it down which is no fun at all.

    How thick do you think that the two layers of cloth will come out at? I can of course just do a tester piece but I thought it worth asking the question here first. Iím guessing 4 or 5mm looks about right,

    Many thanks,

    Nick

  2. #2
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    Depends on how thick your resin is. Does not really matter does it just layer up the material you have most of (ideally the 600) let it run proud and sand it down to a smooth finish. When you are talking in millimetres you would be best off just doing a tester?

  3. #3
    Super Moderator Alex's Avatar
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    That 600 biax is thick, approx 2- 2.5mm depending on how much resin you use but the 280g twill 0.5-1mm so, 3-3.5mm max? I cant see it being any thicker than that. But with all hand layups there is never a definitive answer.

  4. #4
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    Thanks both for your advice. I'll let you know how I get on when I get some good weather and free time on the same day.

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