Gelcoat crocodile

Discussion in 'Boatbuilding' started by codename, May 9, 2012.

  1. codename
    Joined: Mar 2012
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    Location: Latvia

    codename New Member

    Hi everybody!

    We are having a problem with gelcoat AGAIN. After taking the boat out of the mold it always has a crocodile in the laminate.

    What could be the problem?


    Best regards,
  2. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Gelcoat too thin. Gelcoat wasn't cured before laminating. Or it could be other things, it's touchy stuff. Tell us how you catalyse it, apply it, how long you wait before laminating, temperature, etc.

    At the bottom of this page other threads are listed about gelcoat problems. And you can search. We call it 'alligatoring' here.
  3. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    Can't really see picture clearly. Can you give more details as to process you are using? Right now it could be anything.
  4. tinhorn
    Joined: Jan 2008
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    Location: Massachusetts South Shore.

    tinhorn Senior Member

    The gelcoat isn't curing enough before the fiberglass is applied. There are a few possible fixes:

    1. Increase the catalyst level of your gelcoat. I always mix mine as hot as possible.

    2. Gelcoat in the afternoon so that it can cure overnight.

    3. Make sure the styrene fumes can "pour" out of the mold. They are heavier than air. If you can't tip a mold on its side, set up a fan to blow the fumes out of the mold.

    4. Make your first resin layup as hot as possible also. If it hasn't started to gel within 10-15 minutes, you risk the resin attacking the gelcoat. If your resin isn't curing, get it into the sunlight (UV) or set up some heat lamps to start the process.

    Me, I do all four. (And I presume your materials are fresh.)

    EDIT: SamSam is right--the gelcoat could be too thin, preventing a good cure. Your supplier should be able to provide you with a gauge.
    Last edited: May 9, 2012
  5. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    2 & 3 are big culprits. People think there is no time to waste between laminations, but there is a window of time that eliminates a lot of problems. #3 is exactly right.

    Brushing on gelcoat for me has never worked, there were always random thin spots resulting in random alligatoring as in the OP. It works fine for some people though.
  6. frantik
    Joined: May 2012
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    Location: New Zealand

    frantik New Member

    Hi guys im new here and my first post.

    I disagree with hot brew, But agree with gell coat the afternoon before the day of laminating so that the gel coat has 20-24hr to cure.

    I usualy use minimun catylist ratio for me was 1%, but thick layers. I always avoid applying with brush and perfer large 4mm nossel spray gun with gelcoat thin around 10%.

    Also first resin coat minimum catalyst too, @ 1%... But agree temperature and moisture play big role.
  7. tunnels

    tunnels Previous Member

    Bad workmanship is the biggest problem !! Please Dont feel bad !!! 90% of probems with gel coating are human error !!!!.
    Thin gel coat is the first problem
    (the picture i posted was taken of the side of a mould and was thin gell and had slow resin over the top !! i saved it as a perfect sample of aligator or crocodile skin patterns !! ).
    The following are some of the potentual problems that can cause the same thing !!
    under catalysed gel coat and not curing after gel properly !!
    also a slow brew of resin for the first skin !! !
    These are potentually the most common problems but there are many more !!
    Gel coat thickness is very important !! if its thin it will not cure properly!!
    Do you have a special catalyst for gel coating only???? usually there is a special that has long gel time and a short cure time and produces less gasing off during its approach to gel time
    The catalyst ratio should never come below 1.5 % !!
    And if you second coat it should be 2.0 % nothing lower !!!very important .
    another thing thats very important to know is the temprature and the humidity at the time of spraying !!!
    Temprature should never be below 15c and the humidity not above 75% !!
    if the temprature is 20c and the humidity 90% its a killer and you will have slow cure . the same 20c temprature with 65% humidity it will gel much quicker !!
    All are important !!!.
    Tell me what is your spray equipment for applying the gel coat ?? send me a picture please .
    Pressure pot ?? or bigger unit ??
    What the size of the air line hoses you use and do you have water traps and pressure regulators in the system ??
    If you are using a pressure pot then the air to the gun needs to be completely dry !!
    The problem you have could simply be one drop of water come through an airline and through the gun !! its that simple !!! .
    I have lots other pictures and the causes as well just have to find them and post for everyone to see !!.

    Gel coating is an art form and the person gel coating needs to have totall concentration on the job at hand !! no cell phones , no people coming and talking !! if they are not a part of the gel coating team they should not be there !!!.
    One blemish can cause hours and hours of re-work and is really annoying !!!.

    Its quite funny but if you try to replicate gel coat problems its almost impossible to do !!!! i carry a camera with me always when i am in the workshop for just such occassions !!.
    Good luck !! i want to help you !! and give you as much imformation is i can !!:D

    After having a really long close look at the picture you posted it looks like you use a spray gun because you look to have orange peel effect with the coloured pigment !! am i correct of not ?? this could be to higher air pressure at the gun or the gel coat is to thick to come through the gun properly !!.
    Once i see what equipment you have i maybe able to make som suggestions for you to try to improve things for you !!.

    Attached Files:

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  8. tunnels

    tunnels Previous Member

    All on one job !!

    All these pictures were taken on one deck all on one side !! can any one explain why ?? The answers are real easy !!! come on think about it !!look at the product and then think about the mould they are all in hollows or parts of hollows !!

    No its nothing to do with the gel coat and even when it was really thin in most places it still did not aligator so it was cured !!
    Answers !!
    Styrene is heavyer than air so lingers and hangs on in low places and hollows for a long time even all over night !!
    The problems all on one side were because the operaters arm was tired after an hour of holding the gun spraying ! operater error !!!!!
    On decks they use a fine nozzle in the gun to slow the amount coming out so takes longer !!!

    Theres thin gel, there s aligators , theres all kinds of things and some of you have seen ever before . :?::D:p
    WE always spray late afternoon and close up and go home so the gelcoat has roughly more than 12 hours to do its thing !! THere is something about closing up and going home ! any one get the hint ?? Will wait till thursday !!
    This particular problem dosent happen very often and surprisingly there are comanies that never even heard of it . The first time i saw it was vertually the whole side of a 24 foor yacht i had gel coated the afternoon before . it was possible to see what was doing it and all had to do was tip the mould completely upside down ! it was completely hard in less than a hour and we glassed it with out any problems , Did any one get what was happenng ???

    I have lots of picture to do with gel coat so will add them as i find them !! I hope some of it will rub off and some one learns something from it all !!

    Attached Files:

    Last edited: May 17, 2012
  9. tunnels

    tunnels Previous Member

    More gelcoating problems

    My guns bigger than yours !!
    Well it might be and in the hands of someone that dosent listen !! thinks they Know it all ,this is some of the probelms you will encounter along the way !! simply because of lack of understanding and not using a wet film thickness gauge !! It looks like a comb and has teeth set as differant deeths and a number along side !! A absolute must for big jobs
    Top left was just about right and perfect till the gun got to close and the air blew the surface !!
    second top is part of the same hatch cover and you can see the patchs where the gun was held to close !!
    The right side is the side of a hull and a big drift cause by to much gel coat in one area and not using a thickness gauge
    the centre photos the same side just in s diffenat place !!
    The bottom picture was when the mould was rolled over the ends of the drift dripped off the high side and fell onto the botton side and so more problems
    The trouble with drifts is the movment of the gel coat sliding can and does cause the pigment to seperate from the clear gel its mixed into at the factory and gives a strange looking pattern on the finished surface when the hull comes out of the mould Its called Veiling and used to happen a lot a long time ago !! not so much these days !!. The other problems is the excessive thickness shrinks and causes pre-release .
    So know the area !
    know the thickness to spray to
    Know how much to use per sqr metre !
    then you will know how much you will need to cover that area !!
    if all is correct and you have done you sums you should a little left over in the pail !!
    This is so the pump dosent suck air when its being used . and if you are really clever you will have digital 0.00 scales and your gel coat pail on top ! set the quantity and do a count down and when you finished should be on Zero !!
    You will be amazed that in a very short time a good skilled operater dosent even have to watch the scales because he knows instnktively how much is on there !! . He is worth his weigh in Gold and needs a pay rise !!!

    Attached Files:

  10. tunnels

    tunnels Previous Member

    You are sort of on the right path with everything you said just a little extreme !!
    Most manufactures have made there gelcoats to be catalysed at 1.5 % !! dosent Mater where in the world i have worked this is rule of thumb and you can depend on it !! ,
    When you say as hot as possible THAT has no meaning !! you have to specify a % to the kilogram so people will know what you ARE TALKING ABOUT !! .
    Anything over 2.5% and you will get into trouble ! the gelcoat will turn rubbery and will never change no mater how much heat you put on it it will always stay that way !!Beware !!! Good idea to do late afternoon gel coating so no one is likely to put there fingers on it !! just bugs usually !!
    Congratulations you are the first person i have seen that understands about styrene fumes !!
    Now the first layer of resin and glass behind the get coat !! 1.5 % of catalyst in any resin is usualy quite a but quicker than normal ,be carefull ! the shrinkage rate is higher so pre release is something to watch out for !! The other thing to be aware of also is the actual wetting ot of the fibre bundles if the resin is to fast the glass never wets 100% and the dry strands sit till water finds its waY through the gel coat and YOU WILL GET osmosis !!! So dothings in moderation and make a better job . Do you understand the diffeance with P matt csm and Ematt csm ?? Pmatt wets much beter and quicker than most Ematts . The emulssion binder takes time to desolve in the resin and if the gel time is to short from a fast brew then you solve one issue and creat another, thats another set of problems and osmosis !! all done correctly the resin should be thickening in 15 to 20 minutes ! this is a safe zone if it gets to 30 to 40 minutes take the % up a little !! Temprature and humidity play a important role !!! :p

    Quite some tme ago i discovered if you mix a little laminating resin with the gelcoat for a second touch up or whole coat it almost never ever gets alligators ever . easyer to apply and gives a smoother finish . if you suspect there is thin gel drop some gel coat in the laminating resin and colour it when you are laminating hides a multitude of sins !!.
  11. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Some peeps may not know what it is so I'll post this. They are just a piece of plastic or metal around the size of a credit card. Dirt cheap, like a dollar or two. My first one I made myself using a file and feeler gauges, and it worked as good as any. Mark it as thousandths or microns or dime, penny, nickel or like the three bears, too thick, too thin, just right. Whatever works. They can save weeks of work and wads of money.

  12. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Yes styrene sinks AND stinks. You need a fan for curing gelcoat and laminations if it pools in the mold. It rids the shop of some bugs and mice though.

    Styrene is industrial weird. I kind of like the smell, it triggers thoughts that relate to building things, but it can't be healthy. My small shop would get so thick with fumes (I usually wore a respirator) it became impossible to see because my eyes would pour too much water to wipe away. I don't know if it's explosive or not, but I would open the door and stand outside, out of the doorway, and reach my arm around to turn on the lights. Safety First! :rolleyes:
    It saturates your body, my wife would complain of the smell of it at night from my breath while sleeping. I've heard of someone who kept their rabbits in the shop for warmth, when they butchered them they were inedible because of the taste of styrene which saturated them.
  13. tunnels

    tunnels Previous Member

    Been there done that and everything you say is true !! :)
    I remember working inside a boat bonding a hull and deck and dragging my female co worker out into the fresh air and sunshine once !!. :eek:
    Body odor dosent come close when you are styrene saturated and get into the shower , !! Its a good excuse to drink lots a beer but !!Milk is better but not as much fun as lots a beer !! :D
  14. tunnels

    tunnels Previous Member

    I found a wet film gel coat thickness gauge !! this is what the guy dont us !!

    The gel coat pressure pot i made from bits !! it can use the 4.5 litre pot or the smaller 1 litre pot Just simply unclip the airline from one and fit to the other and unscrew the supply hose and fit to the other unit plug in and ready to go .
    The small plastic container will fit inside the pot so cut the top off and mixthe gel coat and place inside ,much easyer and cleaner and can spray multipal colours vertually one after the other just with a quick flush between each colour .
    Pressure pots are a gelcoaters best friend if set up and used properly and most important KEPT CLEAN inside and out !!

    Attached Files:

  15. tinhorn
    Joined: Jan 2008
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    Location: Massachusetts South Shore.

    tinhorn Senior Member

    Forgive me for my lack of precision. As you point out, the recommended percentage of catalyst will vary with temperature (unless, like I was, you're able to control the shop temperature). Hot as possible simply means to use 1/4% more than a reasonable gelcoater would use.

    Same with the first layup of 2-ounce mat. (Yes, I used e-glass.) Use just enough resin to wet out the 'glass, then use a paint roller to mop up any excess. I've only experienced prerelease when I had a thick coating adjacent to a thin coating of gelcoat. (I strive for 18 mils in three passes.)

    Once the gelcoat has properly cured and the skin coat is in, you can complete the layup in a little more relaxed fashion.
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