First layer in making a new mold.

Discussion in 'Fiberglass and Composite Boat Building' started by Fgayford, Feb 7, 2012.

  1. tunnels

    tunnels Previous Member

    i have worked many countries and used gel coat from many differant manufactures and suppliers and they all recomend 1.5 % as a minimum
    Just have to check on the type of catalyst they recomend !!:D
     
  2. Fgayford
    Joined: Nov 2011
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    Location: Cambridge Ontario Canada

    Fgayford Junior Member

    Thanks Herman
    It was on the suppliers label but they aren't the manufacturer of the resin.
    I will ask them about that ratio.
    I have noticed that you have vast knowledge in composites. How did you get this, from schooling, first hand experience or what?
    Everything I know about the subject is from asking people questions and then trying it.
    Thanks Again
     
  3. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    A light buffing of the new mold might take out the possible print through.

    The lower the catalyst ratio, the less shrinkage of the laminate and the less chance of print through. I had enough troubles with alligatoring of gelcoats that I would let it cure over night or more before laminating. Maybe that's why you get print through, the gel is too soft. I would also use resin rich 3/4 ounce mat for the first layer and let that cure for a day, then a 1 1/2 oz mat and let that cure for a day. Then maybe a 3 oz layer of mat and so on until it was done. All of those with the lower end of catalyst ratio. I wanted an adequate but slow cure with no exotherm heat buildup or stressing of the mold. I wanted it stable while it was being made and continuing after it was made.

    Possibly your gelcoat is too thin, allowing print through. Some people use two layers of gel, the second of a different color so as to help show where you are as to depth when doing repairs, buffing etc.

    Not to do with print through, but in molds and products where there are sharp inside corners, like on a flange I would have a sharp edge of mat (as opposed to torn or ragged) butt into the corner from one side and another piece then butt into that mat from the other side. That carried solid glass into the corner instead of the glass bridging the corner and leaving a brittle, resin rich corner prone to chipping. After 1 or two layers of that, a strand or two of roving laid lengthwise in the corner filled it in enough to where the mat had no problem draping the corner. The butted mat and roving made very durable corners.
     
  4. idkfa
    Joined: Sep 2005
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    idkfa Senior Member

    About having the layer cure for a day (shrink) then another, is there a possibility of them behaving like bimetallic strip and inducing a bend into the mould. Infusing moulds seems to be gaining popularity. Maybe if after the first 0.75oz, might be a better idea???? Only asking not suggesting.
     
  5. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    What brand of tooling gel did you buy, or do you know? I ask that because if you purchased it from a retail repackager the instructions they give may not be from the actual manufacturer. It may just be something they came up with.

    There is at least one manufacturer that recommended 1% on tooling gel though, I was a little surprised when I saw it, but it worked for their product. For all others 1.5% is the minimum.

    What resin are you using to skin the part? You need to use a resin formulated to be used in a thin laminate, otherwise it won't cure properly and print is the likely outcome.

    There are also VE barrier coats that are applied before the first laminate to help prevent print through.
     
  6. tunnels

    tunnels Previous Member

    The catalyst regulates the speed at which it goes hard so exsperiment on your own ! mix some at 1% and some at 1.5 % and see what the differance is i could only be a small amount of time differance so go with the higher rather than the lowerand spray a bit quicker or use smaller brews !:D!!.:D
     
  7. SamSam
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    SamSam Senior Member

    In my mind, using the lesser amount of catalyst required for a complete cure reduced possible shrinkage to minimal. Using thin layers reduced the power of a layer of the shrinking glass to deform the mold. As in 1 layer of shrinking stuff has 1/3 the power as 3 layers all shrinking at the same time. So that was my theory on any possible "bimetallic" effect. The first layer of glass had only the resistance of the gelcoat from pulling away from the plug to prevent deformity, which of course was intentionally rendered minimal by wax and pva release to keep the mold from sticking to the plug. The second layer of glass then had the gelcoat and the first layer of glass to overcome, the third then had the gelcoat and two layers to overcome, etc.

    After all the time spent in fairing and finishing a plug to "perfection", I was never in any hurry to rush the relatively unskilled drudge work of making the mold. Or in taking it off the plug or in post curing. I would gradually raise the temperature to the 90s over a week, let it cool for a few days and then I figured if that wasn't good enough, too bad.

    As for infusing, I never did any (just some wet layup vacuum bagging, roughly the same). I would think that until there was a base built up, the pressure of one or two thousand pounds per square foot might be a good way to produce print through, if that was wanted for some reason.

    I'd be interested in hearing what effect infusion or vacuum bagging might have on the stability of a finished piece. Does infusion overcome any tendencies to shrink and warp on the way to full cure?
     
  8. tunnels

    tunnels Previous Member

    There is a required thickness and and a correct catalyst type and ratio they are designed by the manufacture and it is strongly recomended that you use them . Any kind of print through is caused by the person doing the laminating and the schedual of the glass stack .
    Im glad you and i dont work together !,thin gel coat, low catalyst and you are asking for trouble !!,so dont bring your lunch because you will be gone by morning tea time !!:confused:
     
  9. waikikin
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    waikikin Senior Member

    Tunnels, what are you referencing in that quote to come up with that?. All the best from Jeff
     
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  10. SamSam
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    SamSam Senior Member

    Did I say I didn't use the recommended type or amounts of catalyst? Where did I say I used a thin gelcoat? I don't believe I'd work with you anyways, your shop has got to be littered with way too many exclamation points.
     
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  11. tunnels

    tunnels Previous Member

    I spent 2 hours in a meeting talking about poor workmanship and people not doing there jobs properly ,Light, thin or not enough gell coat undercatalysed and so on and so on !!.
    Do what the manufacture recommends ,thickness and the correct catayst ratio and all the problems are history . The place i worked in Korea had the rep tearing his hair out because the company was blaming the product ! introduce a thinkess gauge and ooops problem solved .nothing wrong with the product !!
    Print through then lay a little more csm and use ve resin let it cure and you are far less likely to get print through !Keep those heavy wwoven products awll away from the surface !!
    The other conclussion of the meeting was we get some young new staff and move the older guys sideways Because they have all the answers and the exsperiance but all the bad habits and short cuts that dont work and they want listen and wont learn from there mistakes . Its why the dinosours died out !!They couldnt and wouldnt adapt to change . every day is a new day !! what new thing did you learn yesterday ??
    :p
     
  12. waikikin
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    waikikin Senior Member

    In green is great practice, this was shown to me as an apprentice & would apply it to any "sharp" edge even dagger board edges etc by a top Shipwright, very uncompromising, we worked together in a climate controlled workshop back in 84 on Defense work. I'm so glad to have had great mentors & teachers though out my career. Jeff.
     
  13. Fgayford
    Joined: Nov 2011
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    Fgayford Junior Member

    I just contacted my supplier about the cat %. He said that yes 1% is a starting off point and that yes up to 2.7% is also Ok.for gelcoat.

    General layup polyester is 1% up to 3%
    You guys are the pro's
    Thanks
    Fred
     

  14. tunnels

    tunnels Previous Member

    Test !!I use the bottom of coca cola cans to do all my samples in !! they are shallow and all same size , the sample when its hardened will drop put next day !!start at 1% then go to 1.5% and then 1.75% and take the time . the highter the temprature the quicker it iwll go hard but dont dismiss the humidity level as well . If you glass id damp then the time you had at 1.5% will increase and take longer to harden , you eventual hardeness will never be reached because of the moisture content of the glass !! so keep you rolls of glass in a dry warm place and avoid any problems !!:)
     
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