Paralysis by Analysis... Release wax or PVA for Plug?

Discussion in 'Fiberglass and Composite Boat Building' started by itchyglass, Jan 17, 2023.

  1. itchyglass
    Joined: Aug 2022
    Posts: 14
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    Location: MA

    itchyglass Junior Member

    Hi all... Having read up on this subject in previous posts on this forum, other forums, websites, videos, ect.... I have never read the same thing twice in regards to this topic.

    I covered my 12 foot catamaran hull plug in gelcoat and polished it up to a nice shine. Its not a 100% perfect finish due to some micro scratches here and there but it is beyond acceptable for my case. It is noticeably shiny and reflective. There are more imperfections in the flange (also gelcoat).

    TR waxed and buffed it 8 times by hand.

    My original plan was just to use wax as I had read that in many places. However I have lost faith in getting a nice release from all the varying opinions out there. I spent a hell of a lot of time to get a nice reflection in the gelcoat and would hate to have to use PVA only to refinish the surface of the mold.

    This decision has been 4 days in the making and counting...!
     
  2. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    Either will give you a release,if the surface geometry is correct.Micro scratches become micro ridges in the mould and are easy to polish out provided you have good access.If the wax didn't fill most of the scratches then they aren't really that small and you may have trouble lurking.Scratches on the flanges tend to be of less importance as there is normally a section of flange to create the hull to deck joint that needs to be paid up on them.If you have doubts then use PVA because the amount of work to wash it off and polish the gelcoat is a lot less than building a new plug and mould.Don't go straight to using it on an important project,make a small test section first and observe closely what the effect on the surface is and then lay up a small section so you can see how the surface looks after having the PVA washed off and how easy it is to achieve a good finish.You can even wax over dry PVA for a further experiment.There are different aspects to a moulding situation;getting a great finish is one thing,applying a good release agent is another step,a clean and easy release is the next thing and then you can produce satisfactory components.There is no magic,but it can be a lot of work.Done badly it can be a lot of work wasted and then a major rebuild-its your choice and your work.
     
    ondarvr and fallguy like this.
  3. KD8NPB
    Joined: Mar 2018
    Posts: 137
    Likes: 28, Points: 28
    Location: South Carolina

    KD8NPB Senior Member

    Most sticking failures I've seen are caused by lack of precleaning prior to wax-up.

    For plugs, we do the following;
    Sand up
    Buff up
    Pressure wash / degreaser
    Solvent wipedown (usually a dedicated blended product such as Stoner Kantstik Mold Cleaner)
    Wax

    Buffing compounds tend to contain oils, kerosene, or silicone as carrier solvents for the grit, which will prevent the release agent from spreading and forming a homogenous release film.
     
  4. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    Broadly speaking,I agree with that process-the exception is the pressure washing.Much depends on the material used to construct the plug and if its machined from solid tooling block,it would be safe.If however there is any amount of MDF and the paint has been polished to the point where you can see through it,water is a no-no.In fact I would avoid it as far as possible after a final fine wet sanding.A simple wipe down with a cleaning agent would be enough before moving on to the chosen release agent,which could be wax,PVA or a semi-permanent.
     
  5. leaky
    Joined: Sep 2008
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    Location: nh

    leaky Senior Member

    I'm an amateur at best, take this for what it is.

    I think a major consideration w/ wax versus PVA is the environment you are working in.

    Wax can be applied in practically any temperature. It doesn't care about humidity in practical terms. You can wax something, leave it in a damp garage, a year later you very well might add another coat but you could probably pop a part off it just the same. PVA you can't do that.

    PVA needs particularly reasonable humidity and temperature swings can cause condensation that in a worst case scenario can damage your mold release surface. Even a high humidity period of time can leave it very tacky. It can't be applied in really cold conditions.

    At a minimum I wouldn't use PVA without wax under it. But I'm used to working in tents. Then even the professional boat builders I've met in person, they do not have good climate control where they mold hulls - heat yes but in the summer it's fans, potentially working at night to achieved room temperature, I can't see PVA would be a good option for those (small/custom) operations.

    And PVA adds a water component to the process. Are you setup to use water where the hull will be? Will there be exposed core you might not want to get wet involved?
     

  6. KD8NPB
    Joined: Mar 2018
    Posts: 137
    Likes: 28, Points: 28
    Location: South Carolina

    KD8NPB Senior Member

    In those cases, we use inexpensive aerosol glass cleaner to preclean the part.
     
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