Spraying Gel Coat

Discussion in 'Fiberglass and Composite Boat Building' started by dejavu89, Oct 24, 2009.

  1. BobBill
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    BobBill Senior Member

    Comments on gel vs selected paints?

    Yes, I figured to open up the cracks a bit and fill.

    Gel vs paint? In your view?
     
  2. ondarvr
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    ondarvr Senior Member

    If it actually has crazing, then more work is needed. Crazing is normally from far too thick gel coat, too much thinner and/or from being poorly catalyzed, this means it should be removed before re-coating.

    Cracks can be routed out and filled, but if the area continues to flex the cracks typically return.

    Duratec clear additive makes the work easier, but also reduces the UV and water resistance of the gel coat, it may change the color also.
     
  3. BobBill
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    BobBill Senior Member

    Crazing Cracks

    I honestly do not think the crazing is due to flex. Might be, but hull is quite stiff and very short at 11'7 x 5'.

    It is a 73 hull and likely sat out in hot CA sun for a time also.

    Either way, open and fill needs to be done.

    Then either gel coat or paint???
     
  4. ondarvr
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    ondarvr Senior Member

    Maybe you should post a pic so we can see if its crazing or cracking.

    To use gel coat or paint is up to you. Since the boat is only 11.7' the sanding won't be all that bad if you use gel coat.

    Look at it this way, the prep work is about the same, but when you pull the tape off when using paint, you're done (sort of), with gel coat the work is just starting at that point.
     
  5. BobBill
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    BobBill Senior Member

    Crazing Repair

    Here is one pic.

    Tried to get two spots here, bottom right and top left.
     

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  6. Fanie
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    Fanie Fanie

    That doesn't look like cracking to me. That looks like old paint coming off.

    You get what is called flow coat and is used on the outside where gell coat is used on the inside of moulds. I won't use gell coat or flow coat. Both are very heavy. I would use a high quality two part epoxy paint. It should last as long, save on some weight and is easier to apply. Any time in the future you need to touch up scrapes etc is also going to be much easier.

    Your prep is going to be important. I see lots of elbow grease required :D
     
  7. BobBill
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    BobBill Senior Member

    Crazing

    Fanie, Thanks.

    Another pic. Only in one spot, on deck section and looks worse than it is due to pic conditions and angle.

    I know lots of elbow work needed and the 2-part solution all over. Rub-a-dub ...

    I have some hull wear glass work needed near dagger board slot, but not bad, and have to add some inspection ports to remove the flotation inside.

    Still, not too bad a project for very abused old hull. New goodies are not available for it except at very high costs, (mast is $1000). Class is defunct.

    Am re rigging with Force 5 spars and sail 91 Sq Ft for slightly heavier hull), Laser II rudder assy (has about same surface area to replace barn door), adding flush oar locks (why not?) and removable thwart seat and small outboard bracket (2hp) for occasional need to get out of harbors.

    Should have done this years ago.
     

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  8. BobBill
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    BobBill Senior Member

    Crazing - posted wrong pic

    My dyslexsia at work.
     

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  9. Fanie
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    Fanie Fanie

    The last pic looks different from the top ones. If you could carefully file through the crack to see that it stops at the fiberglass... if the fiberglass broke there are other problems. You could then also determine the thickness of the glass under the gell coat. If it is very thin for the structure it would explain the cracks. If the glass is sufficiently thick then it may be the amount of hardner added to the gell coat initially. A lot of hardner will cure it faster and may cause those cracks. Just enough hardner will take longer to cure but be more flexable (rate of hardning). I also got the impression that the reaction between the hardner and the gell coat continues to spread as long as the mix has not gelled, meaning if you have applied a small area of gell coat (or resin for that matter) then the hardner will try to spread itself evenly through it.

    My one friend's brand new boat developed a crack like that a while ago. It had nothing to do structurally and was just fixed up.


    Have you a picture of the boat as a whole ?
     
  10. BobBill
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    BobBill Senior Member

    Epoxy Curing

    Good observation.

    Am sure the crazing is just through the gel, but no matter on this boat, going to open a epoxy with reinforcement anyway.

    I might add one thing.

    I have been boat refurbishing with glass and epoxy and long crafted lengthy custom spin and fly rods, often employing paste epoxy.

    Sometime back I learned (through some advice) that if you use just a wee bit more resin than hardener, a solid cure is assured, not necessarily faster, but using more hardener usually meant tacky , uncured bond, that might cure in time, but inconvenient. (I did have a local composite materials pal and on-line composite fellow take issue with the idea, but it does work and no failures after 30 plus years.)

    Your advice is well put and will apply it.

    Here is pic of hull.
     

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  11. Herman
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    Herman Senior Member

    Basicly:

    Exact mixing ratio: You get what is stated in the data sheets.
    More resin: More brittle, harder material
    More hardener: More flexible, tougher material

    Unless you go way off in mixing ratio, the curing time is not affected. If it is curing time that you want to change, there are other options. (temperature, amount mixed, different hardener)

    In both options the heat resistance is impaired. Keep that in mind. Some manufacturers have data on this in their datasheets.

    Anyhow, I cannot recommend more then 15% drift, which means a mixing ratio of 100:30 turns into a mixing ratio of 100:25,5 to 100:34,5.

    Do proper testing, and do not use this info if you are not prepared to live with the consequences. Not all epoxy behaves the same. And do not complain to me if things go bad.
     
  12. BobBill
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    BobBill Senior Member

    Epoxy

    I am with you Herman.

    If I strayed it was less than 1% on the resin side and was definitely a function of the application.

    If doing structural repairs, I stay with the formula. This fish rod thingy was to be sure of a hard bond to continue the work. Strength was not significant factor.

    I never complain, when I am responsible, which I are, 99% of the time.

    Good advice, and thanks.
     
  13. Fanie
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    Fanie Fanie

    I apologise - I was assuming polyester resin !
     
  14. BobBill
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    BobBill Senior Member

    Resin

    Fanie, No problem.

    With poly I try to follow, but usually make the stuff a little hot with too many drips, but it is close. I once made a bucket that was smoking after five minutes and learned accordingly. I had to play around a bit to get the feel if it.

    I have had no problems yet. Am using poly for the hull bottom work and may use epoxy for the crazing and will apply paint over. Then again, may just go with poly top and bottom, as easier and the bottom will suffer some beaching-wear that will remove any paint in a short time.

    I appreciate the advice and it was good advice.

    I might add that I use various forms of epoxy resins on my house exterior and some interior sills.

    The paste makes for great repairing of Downy woodpecker holes, with the added pleasure of seeing them try to go back in (stuff is clear) and suffering a bent beak, so to speak...
     

  15. Cobra1
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    Cobra1 Junior Member

    x2 I use it all the time, never did like the BS with wax it in. And it will last for years, my gallon is going on 22, it doesn't take much to put a film on, small touch up gun or fine tip paint gun. Washes out with water, it's the best.
     
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