Don't want to mess up a mold plug

Discussion in 'Fiberglass and Composite Boat Building' started by aaronhl, Oct 1, 2013.

  1. SukiSolo
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    SukiSolo Senior Member

    Well done, that has come out well for a first hit. I'd second SamSam's comments as epoxy sticks out way more than polyester. One other thing is that if there is a lot of return ie sides that are drafted but fairly vertical, the moulding shrinks on as it cures slightly. This can make it harder to release.

    Other ways of popping a moulding can be to try and float it of by injecting water or by putting a couple of tiny holes to allow compressed air in at the deepest points. PVA helps a lot, some use wax/PVA/wax again then PVA again and even then have 'stick out' problems. You can always make some small test pieces preferably well curved say like a can half to try out different waxes. I have had problems that were minimised by better waxes in the past.

    I prefer like SamSam to make plugs in the positive ie convex too. However I like a very solid material to work with usually jellutong, ureol or laminated other solid timber which is then epoxied to finalise shape and finish before taking the mould off. Probably personal but I have found working suitable pattern making timber easier than foam and better definition.
     
  2. SamSam
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    SamSam Senior Member

    PVA is such a flimsy film, I can't imagine waxing over it. Wax on and especially wax off is a fairly rugged procedure. I usually did 4-5 coats of wax and then PVA. If the PVA didn't go on right, I'd wet sponge it off, put on another coat of wax and try again.

    An old foam mattress or some upholstery foam is a good source for sponges.

    I don't know how many parts you are going to take off the mold, it seems you probably only need one, but until 4 or 5 parts are taken off a mold and it becomes seasoned, it's a good idea to use PVA as parts can stick in molds with the same ease and results of molds sticking on plugs.
     
  3. aaronhl
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    aaronhl Senior Member

    Could you guys recommend a good PVA spray can, I don't have a air compressor
     
  4. SamSam
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    SamSam Senior Member

  5. aaronhl
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    aaronhl Senior Member

    Cool, that's a really nice invention, wish I saw that before this project O Well will use it with PVA on the next.

    Does PVA need to be thinned? Or just put it in the jar and spray?

    You said thinned down gel coat, that would of helped give an even apply. Thin it with Acetone? Do you mix it after you have mixed the hardener or all three at once?

    CAN I SPRAY THINNED EPOXY WITH THIS??????????????

    How many OZ can you get until the compressed air is gone?
     
  6. SamSam
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    SamSam Senior Member

    You can thin the pva with water. I think tunnels posted his way of doing it and he thinned it 50/50.

    You thin the gelcoat with styrene first and then add hardener. It's not good for it though, brushing is better. I suppose you could thin the epoxy enough, but why? I'd just use it on the pva.

    I don't remember how long they last.
     
  7. aaronhl
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    aaronhl Senior Member

    I was thinking about spraying a few thinned epoxy coats over these, they are about 21" x 4" wood...from what I have read not many spray epoxy but this piece is so intricate.

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  8. SamSam
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    SamSam Senior Member

    To make a mold from them or are they to be the finished project?
     
  9. aaronhl
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    aaronhl Senior Member

    Finished project, sorry I wouldn't be molding with spray epoxy, just need to cover the wood and eliminate as many drips and runs as possible (if brushed or scraped). If I was to spray it, I could do it on two sides, one at a time, rather than 4. Cut down working time and like I previously mentioned no drips or runs
     
  10. SamSam
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    SamSam Senior Member

    Since the boat isn't in the water for long periods of time, can't you just paint it? What do others do for those things? Spraying epoxy resin or gelcoat never comes out smooth like paint, as paint 'flows' much better.
     
  11. aaronhl
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    aaronhl Senior Member

    You are right, the boat isn't in the water for very long at all, at least not sitting in the water...Most epoxy over the bare wood. Being smooth is the key, but maybe I could spray a few coats of epoxy and sand the last coat smooth at 1000?

    You guys are very nice tending to my thread. I feel like I have learned so much
     
  12. SamSam
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    SamSam Senior Member


  13. aaronhl
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    aaronhl Senior Member

    Good info on that site, I forget to go there, sometimes I just need reminding...Well here is the first piece out of the mold. Just used some fiberglass scraps and epoxy. Pulled it out of the mold while it was still a little soft but not wet. Fits really well all I need to do it paint it

    [​IMG]

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