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Thread: Mono-component polyurethane enamel problem

  1. #1
    Join Date
    Dec 1999
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    Matera, Italy
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    Default Mono-component polyurethane enamel problem

    We are now ready for painting the plywood/epoxy trimaran Seaclipper 20. The boat is made with marine plywood covered with fiberglass/epoxy resin. All the surfaces have been cleaned, sanded with increasing grit (up to 320), cleaned again and perfectly dried. We are using Boero Altura TC mono-component polyurethane enamel (specified for marine environment), Boero Giano primer and the recommended thinner (Boero 703). The building instructions for our boat say that mono-component polyurethane enamel sticks "like crazy" on dry epoxy, neverthless we have made some tests also using a first coat of primer. We used a foam roller in all cases.
    Regardless, we find that the enamel is still somehow soft after two weeks: a little pressure with a nail leaves a dent. What we did wrong? The only explanation to me seems the low temperature: being anxious to start and since the weather had been miserable for many months, most probably we painted at a lower temperature than recommended (below 15C). What should we expect? Is reticulation simply taking longer, or we messed up the whole thing (experiments have been done on the daggerboard only)? Any ideas?

    http://seaclipper20.blogspot.com
    Last edited by pippo; 06-10-2019 at 06:15 AM.

  2. #2
    Join Date
    Oct 2005
    Location
    seattle
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    17,100

    Default Re: Mono-component polyurethane enamel problem

    In addition to sanding, did you wash with water to rid the amine blush? I had a similar problem once thinking sanding was good enough but sanding alone didn’t get rid of the blush.
    Last edited by ron ll; 06-10-2019 at 10:04 AM.

  3. #3
    Join Date
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    South Puget Sound/summer Eastern carib./winter
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    Default Re: Mono-component polyurethane enamel problem

    This is a fairly common problem. Not always, but I see it over and over.

    Avoid it by using an epoxy barrier coat between the epoxy resin and top coat.
    In the states ,this would be a product like Interlux 404/414.

  4. #4
    Join Date
    Jan 2006
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    Oslofjorden
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    Default Re: Mono-component polyurethane enamel problem

    Epoxy must be washed with water
    Ragnar B.

  5. #5
    Join Date
    Dec 1999
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    Matera, Italy
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    Default Re: Mono-component polyurethane enamel problem

    Of course every surface has been cleaned with running water, brushes and Scotchbrites to get rid of the blush

    Quote Originally Posted by mizzenman View Post
    Epoxy must be washed with water

  6. #6
    Join Date
    Dec 1999
    Location
    Matera, Italy
    Posts
    276

    Default Re: Mono-component polyurethane enamel problem

    Is a specific primer of any help?

    Quote Originally Posted by wizbang 13 View Post
    This is a fairly common problem. Not always, but I see it over and over.

    Avoid it by using an epoxy barrier coat between the epoxy resin and top coat.
    In the states ,this would be a product like Interlux 404/414.

  7. #7
    Join Date
    Nov 2011
    Location
    Salt Spring Island, BC
    Posts
    6,502

    Default Re: Mono-component polyurethane enamel problem

    Try warming the daggerboard for a couple of days. A heat lamp should do it.

    Good for you experimenting on a small sample area.

  8. #8
    Join Date
    Jan 2009
    Posts
    331

    Default Re: Mono-component polyurethane enamel problem

    Quote Originally Posted by pippo View Post
    We are now ready for painting the plywood/epoxy trimaran Seaclipper 20. The boat is made with marine plywood covered with fiberglass/epoxy resin. All the surfaces have been cleaned, sanded with increasing grit (up to 320), cleaned again and perfectly dried. We are using Boero Altura TC mono-component polyurethane enamel (specified for marine environment), Boero Giano primer and the recommended thinner (Boero 703). The building instructions for our boat say that mono-component polyurethane enamel sticks "like crazy" on dry epoxy, neverthless we have made some tests also using a first coat of primer. We used a foam roller in all cases.
    Regardless, we find that the enamel is still somehow soft after two weeks: a little pressure with a nail leaves a dent. What we did wrong? The only explanation to me seems the low temperature: being anxious to start and since the weather had been miserable for many months, most probably we painted at a lower temperature than recommended (below 15C). What should we expect? Is reticulation simply taking longer, or we messed up the whole thing (experiments have been done on the daggerboard only)? Any ideas?


    http://seaclipper20.blogspot.com
    Here's a wild idea. Contact the manufacturer of the product. They know it better than anyone.

  9. #9
    Join Date
    Dec 1999
    Location
    Matera, Italy
    Posts
    276

    Default Re: Mono-component polyurethane enamel problem

    Come on... Did that already, waiting for an answer...

    Quote Originally Posted by cbcc View Post
    Here's a wild idea. Contact the manufacturer of the product. They know it better than anyone.

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