Pva separates when applied on mold

Discussion in 'Boat Design' started by Mahp, Apr 14, 2019.

  1. Mahp
    Joined: Apr 2019
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    Location: Tanzania

    Mahp New Member

    I apply wax on mold and buff it off. Then apply pva with a normal kitchen sponge. My pva separates. When i apply pva to unwaxed mold it doesn't. Does that mean wax is the only culprit separating pva. I tried to rub thoroughly the wax coats each at a time, yet pva separates. My instinct says traces of wax are there.
    Also sponge doesnt bring a uniform film when applied for both wax and unwaxed mold.

    Due to these confusion I want to seek advice here with years of experience you have.

    I am new to fiberglass. I love fiberglass!
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    There are some very experienced people here who will help. Your method of application may be part of the problem, some advise fine mist spraying, allowed to set-up for a short time, then re-spraying the whole thing. The key seems to be to get a little on to begin with, when that has dried then another application can be made, otherwise trying to go too heavy at the start leads to beading. I have heard of people putting washing up detergent in it to lessen the beading, but I'd wait for better advice from the moulding experts here, before trying that.
  3. Sparky568
    Joined: Jan 2017
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    Sparky568 Junior Member

    Everything has a purpose. If you are applying wax to a smooth mold i.e. your first coat of resin is gelcoat as a finished surface the PVA is unnecessary and will "bead up" when applied possibly making a rough surface. If the part you are making will be finished later or, you need to add glass later and you are just applying resin and fiberglass use PVA. It will wash off easily with warm water after pulling it from the mold. This will help with further lamination without worrying you got all the wax off.
  4. Doug Halsey
    Joined: Feb 2007
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    Doug Halsey Senior Member

  5. Mahp
    Joined: Apr 2019
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    Location: Tanzania

    Mahp New Member

    My mold is not 100% smooth. Some very light scratches are there, so wax alone is giving a hard time to release the part, I want to use pva too as a second barrier.
    My wax quality is intermediate. So pva can help along with wax. OR perhaps pva alone on unwaxed mold.
    If i apply wax and pva then pva separates, as I mentioned on my very first question I posted here.

  6. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    PVA works great, but can be difficult to apply correctly.

    If you don’t plan to spray it, then use a rag and wipe it on.
    Don’t put much on the rag and only do a small area at a time (1’x1’ ).

    Wipe until it starts to dry, and don’t overload the surface. You won’t see in on the surface, but it will leave a uniform smooth surface if done correctly.
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