PVA Mold Release Required or Not?

Discussion in 'Fiberglass and Composite Boat Building' started by fly186, Dec 12, 2016.

  1. fly186
    Joined: Nov 2016
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    fly186 Junior Member

    Hey folks, first post here on this forum.. most likely the first of many.
    I'm preparing to build a hardtop for my center console. I'm making a male mold using some 4'x8' whiteboard material available pretty cheap from Home Depot.
    It''s called "Thrifty White Tile Board". This will be a one-time mold and the surface area is about 50 ft sq with a slight side-to-side camber.

    I'm planning to vacuum bag this thing but the question is about whether I should spray that smooth non-porous whiteboard surface with PVA or if it will be sufficient to just wax it really well.

    Full disclosure... I've never made anything close to this size and also have never vacuum bagged anything.
     
  2. ondarvr
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    ondarvr Senior Member

    I haven’t looked at that product, but if it’s the typical plastic coated wood (or something), then it normally doesn’t require PVA, the surface works with just being waxed, but….

    PVA is an insurance policy that helps if the surface hasn’t been waxed just right, or for some reason it just wants to stick, so people that feel lucky may not use it, others won’t go without it. Anytime you have body filler or some other type of soft, non-tooling type product surface, PVA may be the only way to keep it from sticking.

    You can wipe PVA on and it works well, plus doesn’t make a mess.
     
    Last edited: Dec 14, 2016
  3. fly186
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    fly186 Junior Member

    Thanks for the quick response. The areas that concern me are the three seams that will exist between the panels. I was going to use clear packing tape over them and then wax the whole thing with a few coats but it might be less work to give it one coat of wax then spray on the PVA and not worry about it.
     
  4. ondarvr
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    ondarvr Senior Member

    You need more than one coat of wax, PVA doesn't really replace wax.

    The packing tape is fine, it should work well.
     
  5. Jim Caldwell
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    Jim Caldwell Senior Member

    If it is beaded Styrofoam, don't do it.
     
  6. SamSam
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    SamSam Senior Member

    I made a female 16' jonboat mold out of the stuff with Bondo in all the corners. I waxed it and wiped a coat of pva on it, the boat came out easier than most made in a fiberglass mold. You could probably get by with just wax, but why try? It's not much effort to apply the pva.

    As always you could try a test piece, I'd try one section waxed, one waxed plus pva and one with nothing at all, just to see what happens.

    Why are you making a male mold? I'd rather have the top smooth so it won't get so dirty.
     
  7. fly186
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    fly186 Junior Member

    Good question about why the male mold. Mainly because that's how I've seen it done a few times. I also want the bottom to be smooth. I expect to do some fairing on the top after 1708 and then 10oz glass. Hoping it won't be too bad if using peel ply.
    Top and bottom will be primed then painted with Awlcraft.
     
  8. SamSam
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    SamSam Senior Member

    I was going to ask in your other thread (about sanding ridges etc) but it;'s probably best here. How did the tile board work? What did you do for release?
     
  9. fly186
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    fly186 Junior Member

    The tile board or white dry erase board stuff from Home Depot worked great. I gave it two coats of wax and had no problems at all with releasing the part after vacuum bagging. The packing tape on the seams worked well also. The bottom surface on my top that was against this stuff is perfectly smooth and will be ready to paint after some light sanding on the seams. Cost is about $12 for a 4'x8' sheet.
    Here's a picture of the mold and then one of the vaccum bagging underway.

    TopMold.jpg

    TopInTheBag.jpg
     
    Last edited: Jan 4, 2017
  10. jorgepease
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    jorgepease Senior Member

    what's the pvc pipe for, is that your vacuum? You only need a single point to bag that part. That pipe will cause ridges.
     
  11. fly186
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    fly186 Junior Member

    Where were you a week ago? :D
    Yes, I had a lot of ridges to contend with but didn't know that a single point for the vacuum port would work but it definitely would have. Live and learn.
    Thanks.
     

  12. jorgepease
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    jorgepease Senior Member

    Sorry )) ... I did the same thing long ago!! lol
     
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