Infusion - gelcoat pre-release

Discussion in 'Fiberglass and Composite Boat Building' started by bedfordd, Jul 23, 2019.

  1. bedfordd
    Joined: Apr 2013
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    Location: San Diego

    bedfordd DonnieB

    I build 8' sailing dinghies (prams) used mainly for teaching kids sailing but are also raced out here in California. I'm always concerned with hull weight (about 38lbs) and hull finish. I'm on boat #35 and still get some pre-release in the chines area in about 50% of my boats coming out of the mold.

    My process is:
    After waxing and PVA, I spray 5 16oz cups of gelcoat to about 15mil thickness using alternating passes of fore-aft and side-to-side. After curing, spray 1 16oz cup of VE primer. After curing I lay in a small strip of roving / VE in the chines and along the top of the hull to prevent voids. I then lay down a veil to help with print-through. Then lay in 1 layer 17oz stitched, 1/4 foam core (or 3mm Soric on sides), and a layer of 17oz stitched cloth.

    The layup usually goes in the day after the gelcoat and the infusion starts the day after. I use VE infusion resin, pull about 27 - 30Hg during my 40 minutes infusion (takes 3.25 gallons) and then I turn down to 25Hg for about 4-8 hours. I usually move the mold into the sun the next day and try to release the boat. My last boat had release over about 20% of the chine area (mostly the bottom) of about 1/8th inch deep by 1 inch wide.

    My question, what cases pre-release? I thought too much build-up of gelcoat, thus my spray pattern. I was thinking of laying is 3" CSM tape over the gelcoat in the chines but that is just guessing at a solution. I appreciate your ideas!

    PS, I'm also looking for suggestion of an adhesive I can use to adhere 1/2" foam or wood to my bow thwart (hand layup) for the mast partner. I've been using Duraglass but I often find the core/glass separate when I drill the hole for the mast. Thanks!
     
  2. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Typically the reason for prerelease is uneven gel coat thickness, with too much in one area. It can also be aggravated by the type of mold release.

    Try to get the gel coat on as even as possible, plus place a fan so it blows into the mold as it cures. This will help to achieve an even cure of the gel coat film.

    If the mold is in good shape you shouldn’t need PVA, just wax should be enough. It may have an affect on the prerelease too.
     
  3. bedfordd
    Joined: Apr 2013
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    Location: San Diego

    bedfordd DonnieB

    Thanks ondarvr, I like the fan idea to blow out the styrene from inside the female mold. I'll check again when I spray w/ the gauge but I've had good luck with measuring even sprays in the past. Yes, I usually only spray the PVA on non-race boats. I'll see if there's a correlational.

    -don
     
  4. rob denney
    Joined: Feb 2005
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    rob denney Senior Member

    I would look at the bag bridging the chine area.
     
  5. bedfordd
    Joined: Apr 2013
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    Location: San Diego

    bedfordd DonnieB

    Yeah, I try to tuck the bag into the chine to keep the weight down but I'll look at it again with my next infusion - thanks!
     
  6. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    Make sure the wax is thoroughly buffed of with a clean rag to avoid surplus gassing off the gelcoat.
    Don’t over wax, after the initial first 3 pulls you should get 3-4 parts before re waxing.
    Keep out of direct sunlight, avoid hotspots.
    If your using veil (tissue) what’s the primer coat for ?
    I’d put the veil in first and then the rovings in the chine etc
     
  7. bedfordd
    Joined: Apr 2013
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    Location: San Diego

    bedfordd DonnieB

    Thanks redreuben. Good point about excess wax. I'm a little gun-shy about release as I've had to trash a mold after a boat stuck and then had another boat stick in the current mold. After re-surfacing this mold, I've probably pulled six boats. I now lay down one layer of wax and polish. If not a race boat then I spray PVA just to be sure (no PVA to get a nicer finish).

    The veil and VE primer is just to reduce print-through. These dinghies are dry stored so I don't need any kind of barrier coat. My foam is grooved on both sides so the bottom can look like a waffle iron after infusion!

    For the boat I infused yesterday, I laid in 4" CSM tape in the chines, no veil nor VE primer. I just popped it out and no pre-release and very little print-through (so far). I do think it is my gelcoat spray technique that has the most to do with pre-release. I just have to be very conscientious about laying in a consistent layer with no extra in the chines..
     
  8. redreuben
    Joined: Jan 2009
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    Location: Beaconsfield Western Australia

    redreuben redreuben

    In my experience pre release is mostly from not giving wax time to dry hard. Same with sticking to mould, many people put the next coat of wax on as soon as they have buffed up the last one, doesn't work, you have to give it time to dry.
    4 coats of wax back to back is one coat of wax. Wax the mould, let it dry hard, then put another coat on, that way you get a build up.
    Print through; Whatever you use as a skin coat, tissue, 225gm csm or whatever the harder you cure it the less print through you'll get. You can always give it a wipe with acetone if your scared about bonding but its never been an issue for me.
    Building Farr 9.2's we skinned with 225 split strand csm and Vinylester, left over the weekend hot weather we got no print through from the contour foam. The main lay up was stitched biaxial.
     
  9. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    How you should apply the specific wax is written in the directions on the can, read them. Some say let it haze over then buff, others say “don’t let it dry” wipe off immediately. They will also let you know how long to wait between coats for that exact wax. I shouldn’t say just wax, any mold release will tell you how to use it.

    The rules aren’t universal, don’t assume you know how to use it.
     

  10. Steve Clark
    Joined: Jul 2004
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    Location: Narragansett Bay RI

    Steve Clark Charged Particle

    Tight bag, cloth or process materials bridging the chine.
    Change cloth cut so that one piece butts into the corner and the other overlaps.
    This will give the glass relief enough to go into the corner.
    When the vacuum is drawn, the reinforcement is pushed out to the tool surface, which means the patterns have to grow a bit, the only way to do that is to have slip joints ( overlaps).

    All the other stuff is also true, but my bet is tight material.
    SHC
     
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