Difficult to release (small mold) - recommendations

Discussion in 'Fiberglass and Composite Boat Building' started by mrdebian, Sep 5, 2021.

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  1. mrdebian
    Joined: Apr 2021
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    Location: Greece

    mrdebian Junior Member

    Hi all,

    I've got a small mold for a kayak hatch which has space of around 15 litres to get an idea about its size.
    I guess due to its shape is very difficult to release when creating an item from it.
    I released from it so far 20 items but each time is a pain to release it.
    Each time I'm using 4 layers of wax and sometimes even more.
    I tried also 4 layers of wax and PVA but more or less the result is the same. Difficult to release.

    Any recommendations are more than welcome.

    Kind regards,
     

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  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    That looks like an item that was not made with precision in mind. I think if there are constant difficulties, it might be easier to start again, than to persist with it, it is after all a pretty small thing with no great complexity to it.
     
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  3. ondarvr
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    ondarvr Senior Member

    What is the mold surface and what wax are you using?
     
  4. jehardiman
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    jehardiman Senior Member

    Yeah, it doesn't look very fair. Any little dips and imperfections in the surface are going to cause problems.
     
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  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    You need to fair and sort of finish the mold surface.

    Duratec primer works nice.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I have to say, it looked so much like the old tin stump caps off the old wooden stumps I switched out under the house, I thought "that is where they got to" !
     
  7. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    @ondarvr it is just fiberglass (chopped mat with resin) as the final product is also from it.
    Do you believe that if I clean it well with acetone to remove the wax and paint it with gelcoat (sand, polish afterwards) will be easier to release?

    I'm adding directly to it resin with the chopped mat, no gelcoat as I don't want the product I'm getting out of it to have gelcoat.

    Thanks
     
  8. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    You'll need to clean and sand it before putting gel coat on it.

    A mold surface like that tends to not release well, and a part made without gel coat doesn't release the well either, so it's a double whammy.
     
  9. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Initially I thought the picture was of the back of the component on the mould.If that really is the mould surface,its hard to believe it was ever made to serve as a mould.The OP states that he doesn't want a gelcoat finish and this seems odd.What is the perceived advantage that comes from a resin/mat surface?Beyond the need for a better surface it would be wise to either extend the flanges to make releasing the part easier or to include a blow hole to get the central area free.
    With a decent surface that has been well prepared with wax I wouldn't expect to use more than one coat of wax per component after the first two or three parts have been made.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    My hat blew off a while ago when I was walking across the road, it got ran over by a semi-trailer (an 18-wheeler in US -speak), it still looked better than that mould !
     
  11. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    @wet feet I don't want to use gelcoat on the item that I will release from the mold but on the mold itself is fine to use gelcoat.
    I released another item from it, used some epoxy putty to fix it a little bit and a primer afterwards (like the Duratec that is been recommended here).
    I will have to sand it and polish it and maybe I will have to use more putty to make it smoother in some areas.
    Anyway, assuming that is done, my question is if I can use the mold as it looks now (without gelcoat) to produce items; that means that I will appply the resin/mat direct to that surface with the primer.
    Would that cause a problem or I will have to use the mold I got in the picture (after finilizing it) as a plug and make a mold out of it (with gelcoat).
    Even if I do the latter then would it be fine to apply resin/mat direct to the gelcoat surface without adding gelcoat to the item that I want to release?

    Thanks
     

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  12. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Primers work well enough for a few parts, but the primer won't hold its gloss very long. The dull surface won't release as easily as a high gloss finish.

    Not using gel coat on the part will work, but again, the part won't release as easily and it will tend to form a dull scum on the mold surface. The part will also have noticeable strands of glass on the surface, not a good look if anyone can see it.

    If you are only making a few parts it may not matter much though.
     
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  13. mrdebian
    Joined: Apr 2021
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    mrdebian Junior Member

    Thanks a lot @ondarvr for the detailed answer.
     
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  14. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Buy a gold pan and use that for a mould, that is just junk
     

  15. Kayakmarathon
    Joined: Sep 2014
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    Kayakmarathon Junior Member

    It might be simpler to build a box from flat pieces of multilayered fiberglass than to risk getting the product stuck in the mold.
     
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