Building parts with a flat (not glossy) finish from mold

Discussion in 'Boat Design' started by Hatfield32804, Nov 8, 2021.

  1. Hatfield32804
    Joined: Sep 2018
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    Hatfield32804 Junior Member

    Starting a new project.

    The goal is to build 12' fiberglass duck boats using molds we are building. Visually the finished product will look similar to a kayak.

    Since it will be used for hunting, I would like to be able to be able to pull parts that have a flat (not glossy) finish from my mold.

    At this time, my plan is to construct boats using hand layout method with gelcoat against mold surface.

    My molds were build from a plug with a highly refined surface (wet sanded to 3000, compounded and polished before waxing).

    What is the best way to go about making this happen?

    Obviously there are a few possibilities that come to mind. However, I'm a big believer in following in the footsteps of those who have gone before - and most likely know way more about industry standard practices than I do.

    Attached a photo of mold for bottom half of boat for reference.
     

    Attached Files:

  2. wet feet
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    wet feet Senior Member

    It would cause me great anguish to destroy a nicely finished surface on a nearly new tool.The simple solution might be to ask a local supplier of car paint for a sample of clear 2 pack lacquer with enough flatting agent added to give the low level of gloss that would satisfy your needs.Long term you would have to abrade the surface of the mould to break down the smooth surface.You could attack the surface of the boat with a sander,but would have to be careful not to wear through the gel and allow water to penetrate,which is why I would advocate the flat lacquer approach.For any future parts you might consider not polishing the plug to a high gloss,textured surfaces will normally release if there is ample draft on the component.You may have seen the imitation old time beams that go into new buildings-they came out of a mould of some sort.
     
  3. Hatfield32804
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    Hatfield32804 Junior Member

    Regarding the 2 pack lacquer option, this would be applied after part is pulled from mold, correct?
     
  4. wet feet
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    wet feet Senior Member

    That's the way I would do it.I recommend trying the technique on a small test piece first.
     
  5. fallguy
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    fallguy Senior Member

    @ondarvr is the local expert

    don't touch your molds until you have a chance to hear his opinion

    There are others here knowledgeable as well.
     
  6. fallguy
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    fallguy Senior Member

  7. Hatfield32804
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    Hatfield32804 Junior Member

    Understood and agreed.
     
  8. Hatfield32804
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    Hatfield32804 Junior Member

    Sounds good.

    I am not looking to rush into action until there's a solid plan in place.

    I seem to recall hearing that cabosil mixed with PVA then sprayed on mold would produce parts with a flat finish. Can someone speak to this as a possible system to use in my application?
     
  9. wet feet
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    wet feet Senior Member

    As before,try a small test piece first and any shiny surface will be good enough to experiment with.You don't even need to produce a part since the shine you see will be a part of the finished object.Which doesn't mean you can't try a section when you have a promising surface prepared.
     
  10. rxcomposite
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    rxcomposite Senior Member

    Spray a heavy coat of Partall (PVA) before laminating. Partall may still be smooth to your liking but it will lose some shine of the polished mold. If you still don't like it, sand the finish part to give it a dull finish. You can omit the gelcoat and just spray paint it with automotive mat finish.
     
  11. rxcomposite
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    rxcomposite Senior Member

    It will give you a textured surface but it might still be glossy to your liking. Try scotch bright to dull.
     
  12. Hatfield32804
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    Hatfield32804 Junior Member

    Any thoughts on a good ratio of pva to cabosil I could use to start test pieces?
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    I seem to recall there was another thread on this very subject, how to find it might be the problem, but as mentioned, ondarvr is definitely the source to seek the opinion of, he has a wealth of knowledge in such matters.
     
  14. ondarvr
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    ondarvr Senior Member

    You can buy a Teflon mold release that will give you a flat finish on the part. Some of my military parts manufacturers use it. It's not exactly a cheap or easy process for a low cost hunting boat though.

    A low or no gross finish out of the mold can be achieved in a couple of ways, but doing any repairs or touch ups to the part means it needs to be completely resprayed. And a resprayed non gloss part won't match an inmold non gloss part.

    If you really want a non gloss finish, sometimes painting is the easiest way.

    I think they changed the product designation a while ago and I don't know the new code. You may need to contact them.

    https://miller-stephenson.com/chemicals/mold-release-agents/
     
    Skyak and Hatfield32804 like this.

  15. Hatfield32804
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    Hatfield32804 Junior Member

    Thank you sir, I appreciate the info. I will contact Miller Stephenson tomorrow to determine the specific product.

    I understand there are challenges associated with touch up/repairs to both the tool and any parts that might be built with a flat finish.

    It’s nice to be able to quickly buff out imperfections to restore a high gloss finish.

    IF I did decide to paint each part, would you agree with poster above that using a 2 pack clear over colored gel presents the best option? (As opposed to a colored 2 pack poly or similar).
     
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