Gel coat

Discussion in 'Materials' started by nrodes, Jan 22, 2009.

  1. nrodes
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    nrodes New Member

    Is there a way to make a smooth gel coat without a female mold? I know surfboard makers do that alot but im just wondering if its practical on a 25 footer and how you would do it if it is.

    thanks
     
  2. ondarvr
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    ondarvr Senior Member

    There are products you can add to gel coat that will allow it to level and flow better, the problem is they tend to degrade the gel coat, reducing it's water and UV resistance. For the most part it's a spray it on as smooth as possible, then sand it down until you're either pleased with the finish or tired of sanding type of job.
     
  3. mark775

    mark775 Guest

    You have to be willing to go through the grits. I´ve done it, it´s a pain but worth the effort. You can roll it on, as well, but even more of a pain fighting stipple. Don´t stop until 600grit, min., thousand, or more, is better - stop sanding before you go through (easily said). Buff out, WAX! Good luck
     
  4. Cobra1
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    Cobra1 Junior Member

    If you thin it out use styrene, acetone will work but it makes it softer. The softer it is the esier it is to sand out, but it scratch's easy.
     
  5. ondarvr
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    ondarvr Senior Member

    Styrene can cause premature yellowing, less water resistance and possible cracking. The best products are from the gel coat suppliers, most have some type of a patchaid that will improve the sprayability and cure with fewer negative affects.
     
  6. Cobra1
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    Cobra1 Junior Member

  7. mark775

    mark775 Guest

    I agree with Ondarvr and styrene is bad for everything from the environment to you to your un-conceived kids. (I sometimes use it tho)
     
  8. ondarvr
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    ondarvr Senior Member

    Maybe 40 years in F/G and working for a company that formulates and manufactures gel coat and resin trumps second hand information from a retail supplier that talked with some unknown person.

    Sorry for that, but adding styrene, and 75% at that, is stupid, being smooth means little, it should be when there’s almost no base resin left in the mix. Styrene is the main ingredient that yellows in gel coat, removing styrene and adding MMA typically improves weathering, adding more styrene almost always speeds the yellowing and I'm talking about just a small add (3-5%), at 75% you just applied a bunch of junk. Many of the negative affects of adding high levels of solvents or monomers to polyesters don't show up right away, but the physical properties will be degraded and it will fail far sooner than unaltered products.
     
  9. mark775

    mark775 Guest

    Ondarvr, I just have practical experience in this area (no chemistry)...What is MMA?
     
  10. ondarvr
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    ondarvr Senior Member

    Methyl Methacrylate.
     
  11. mark775

    mark775 Guest

    Thanks. Don´t see that on the store´s shelves...
     
  12. Cobra1
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    Cobra1 Junior Member

    And you will find styrene in resin as well.
     
  13. ondarvr
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    ondarvr Senior Member

    Yes, styrene is a very important component in both resin and gel coat, but there's been a great deal of research done to find the right level. Before the federal "MACT" (Maximum Achievable Control Technology) and "HAP" (Hazardous Air Pollutants) regulations were put in place styrene levels in resin and gel coat ranged from around 38% to 50%, now depending on the industry, gel coat is either 30% or 33% and resin is 35%, this is for open molding. If you're a small user, or need to use Specialty products you can still use the older, higher HAP% products.

    Before these regulations were put in place nobody found higher levels of styrene to be good for polyesters, if they had found 65% to work better than 48% it would have been used because styrene is far less costly than base resin.

    Without styrene polyesters wouldn't be usable, because at room temperature un-catalyzed resin would be considered a solid without it. Styrene also aids in the crosslinking to achieve a better cure, but when you pass the point of better cure and usability (spraying and/or wetting out glass) the limitations of styrene become evident. The down side of more styrene is less UV and water resistance and lower physical properties that typically result in a weaker, more brittle laminate.

    So if the gel coat started at 40% styrene (small user) and you add another 75%, the styrene % in the final product would be around 65% and the base resin would be reduced by about the same amount. What you end up with is a much lower pigment % and pigment content is used to achieve the correct color and 90% of the UV resistance, at this lower pigment % gel coat will be more translucent and yellow sooner even if the lower % wasn’t due to the added styrene. You also replaced base resin (strong, resilient, water resistant and somewhat good UV resistance) with styrene (weak, brittle, poor water and UV resistance), so you tell me which repair will be better and last longer.

    Now if you have a few decades of formulation and lab testing data to show this isn’t the case, please let the rest of the industry know about it.
     

  14. ondarvr
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    ondarvr Senior Member

    You won't find it anywhere, but it is used in some patchaid type products to help reduce the viscosty and keep some of the UV resistance, high end gel coats may have MMA in them already. If you're in Homer AK even the patchaid products will be difficult to find, Anchorage would be the closest place.
     
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