gel coat problem

Discussion in 'Materials' started by harrier spiro, Aug 3, 2010.

  1. harrier spiro
    Joined: Aug 2010
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    Location: melbourne australia

    harrier spiro Junior Member

    heres a couple of pics of the problem it seems its flat in sanded mode but soon as you hit it with the buffer things appear...:confused:
    you can see in pic one the surface b4 its been touched up second one is light 2000grit wet it "talks to you" can see the highs coming off then after buffed and polished some thins reapear gone over it really deeply in places with heavier grits up to 2000 again and they still remain...divits, pits , creators.looks like the surface of the moon and deeper you go then other probs like pin holes very very tiny ones...not really bothered by them at this still has shine overall but surface wise far from what id call mirror..

    Attached Files:

  2. tunnels

    tunnels Previous Member

    Never listen to or trust a salesman !!!

    Those are really good pictures and show lots a detail !!, what we needed in the begining !who ever took them Thank you !!
    Your second heavy coat behind is the problem , Because of the splatter effect of the spray pattern it has drawn the thinner layer of the surface coat , For want of a better word its print through !!
    Try and sand a patch first with 400 grit sand paper then 600 grit , 800grit then 1200 and buff lightly and dont heat the surface with the buffing pad Because i also suspect the get coat is not that hard and heating with the buff pad could simply make the pattern reappear again !! tread very carefully .
    I would like to hear how it works for good or bad !!! need some feed back please!!!
    In one way you were very luck not to have ended up with aligators all over the moulds surface because of the second heavy coat that was sprayed over the uncured still gelled but soft first coat .
    Like some one has already said it should have been a one coat situation !!
    fine flick coats and then another fine flick coat finishing off with the final coat to get the required thickness all at the same time with very little delay between , all wet on wet .
    Understand the product and how it worksand what it does then you understand what is required to make it work like it should .
    Trying to replicate these problems on test samples is usually very hard to do !!. :confused:
    The sales man that gave you the low down should be made to roll up his sleeves and help you sand and polish and buff . Get a hold of his Boss and give him a earful of what has transpired because of the misleading information you were given by the companies representative .
    Think on the positve side it will be a good learning exsperiance for the saleman , his boss and the company !!
    Good luck :D
  3. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Thank you for your nice compliment.

    Sales manager at a composite distributor in the Netherlands.

    As for this poor guys mold:

    There is a gelcoat problem, and no-one can deny that. But tunnels is right about the buffing: On a green mold, and actually always, try and avoid bringing in any heat from buffing. This required a different approach then buffing a car. Cars are metal, heat is conducted away from the source. GRP is a completely different material, which does not conduct heat so nicely.

    As for gelcoat porosity: There is a lot of factors that can create that, application is one of them, and the situation can be improved by using a different MEKP curing agent (Syrgis Andonox MEC is one of them). Also check your MEKP for water content. (mix MEKP in a glass tube, with the same amount of styrene. Shake vigorously for 30 seconds. If the mix went hazy, there is too much water in the MEKP.)

    Has this mould been built in tooling gelcoat? What is the Tg of the gelcoat?
  4. harrier spiro
    Joined: Aug 2010
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    Location: melbourne australia

    harrier spiro Junior Member

    thanks mate i took the pics...hmmm doesnt seem so bad now...phew haha
    yes it was tooling gelcoat..the tg? i have no idea?...but im going to find out
    and we did use andonox mekp

    alwready going ahead with the sanding thank you and ill put more pics up of the results...
    gel does feel a little soft as well can mark with a fingernail
  5. tunnels

    tunnels Previous Member

    You can mark it with a fingernail !!!! wow that soft . :confused:
    Turn the mould upside down and put a plastic skirt from the mold to the foor and put a small blower heater in there and warm the whole thing The heat will hang inside the hull as it rises . Could need 24 hours or longer but you should not be able to even leave anykind of a fingernail mark on it . Do some back tracking and ask around about the catalyst and the ratio and triple check if what you got was what is should have been .
  6. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    I second that. Tooling gelcoat should be really hard. Even without a postcure. Do you have a barcol hardness tester? It really should read 40 or up.

    Do you still have gelcoat left? Could you make a test piece? Apply gelcoat thick enough (0,7mm) and apply a laminate. Do a barcol test on that as well.
  7. harrier spiro
    Joined: Aug 2010
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    Location: melbourne australia

    harrier spiro Junior Member

    yes getting a barcol tester in at the start of the week...after the post cure is done...turned the mould upside down and put a plastiv drop sheet over it to the floor and got a heater in there atm will prob leave it like that till sunday morning..heat inside the mould is 50 deg celcius at moment...
    and well be making a few other test peices some to try and replicate our mistakes and some to see if the gel tooling gel coat is within its shelf life also and finaly a few others to to see what works best we have andonox mekp and butenox mekp as well wich gels qicker from previous experiances

    this site is a wealth of tech knowledge thats invaluable..i like to get to the bottom of things and have the knowlege to do the best practices i can no matter how in depth i have to go.....
    at this stage it looks to be a few problems that you guys have reconfirmed
    in my mind i have a fair understanding of things grp but obviously ive only scratched the surface of what i should know...
    ive been a fabrication engineer for the last 10 or so years and the last year or so ive made the change to grp boat building its going to be a long road no doubt but ive got a thirst for knowledge and love boats and doing things the rite way...
    what ive ive found so far is alot of contradictory info out there and nothing beats test pieces lol this was an expensy lesson learned but in hindsite..ill prob make a peice out of this mould and use it as a plug for a new one..alot of work, time and money down the drain but nothing comes easy when your a reletive beginer ive produced a few articles wich have come out very nicely...but the deeper i dig i think they might have been flukes haha
  8. rxcomposite
    Joined: Jan 2005
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    Location: Philippines

    rxcomposite Senior Member

    Very accurate infotinhorn. You deserve some points.
  9. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    It looks nothing like alligatoring, its post cure in an under cured laminate and/or gel coat layer. One pic shows some actual small pits that could be air pockets or uncured droplets behind the gel coat.
  10. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    This is alligatoring, and some causes and remedies: (above indeed is not alligatoring)

    Alligatoring / Wrinkling
    Effect - Wrinkling of gelcoat in contact with the mould. Air or laminating resin may be trapped in ridges on the wrinkles.

    Cause Remedy
    Insufficient film thickness Apply recomended thickness (400 -600 micron)
    High humidity Install dehumidifiers or work in a less humid environment
    Low temperature Increase the room temperature
    Too low catalyst level Increase catalyst level
    Too long gel time Check catalyst level
    Insufficient cure time before back up Check catalyst type / level / temperature


  11. zerogara
    Joined: Aug 2004
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    Location: Preveza

    zerogara build it and sail it

    One wild guess, as nobody has talked about the plug. Was this an older hull?
    Is there a chance somewhere along the line of finishing the plug and waxing it the plug was contaminated with a silicon product? I don't allow anything containing silicon to come within a distance from my work area.

    What is the chance of the catalyst being bad? They are peroxides (hyper-oxides) meaning they release oxygen and if they get old or left uncapped for a while they lose this capacity and therefore act as less catalyst or no catalyst. Meaning your gel coat (as others have mentioned) is not fully cured. Test a small area and spray some thinned catalyst on, when it dries spray PVA on and give it some time. See if this area becomes harder and more stable to finish than the rest of the mold.
    If gel coat is not cured yet and it is exposed to air it will never cure until air is sealed off of it. If it takes a while to produce one piece make the sacrifice of having to do more work to refinish the first piece and redo the mold after the first run. The amount of time and heat released from the first run may help fully cure the tooling gel coat.
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