Gel coat additives

Discussion in 'Materials' started by jimn, Aug 30, 2014.

  1. jimn
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    jimn Junior Member

    I'm preparing to re gel coat my 25' fishing boat, my gel coat supplier told me I should mix a product called Simtec "super clear" to help it spray and level, my problem is I don't want a gloss finish The manufacture claims the product helps prevent the gel coat from orange peal and pin holes plus it air cures so no need for surfacing agent, I thought I would mix it at a 25% but the manufacturer said I would not get the air cure properties and doesn't recommend using a surfacing agent. So I guess my question is, what can I mix with my gel coat to help it spray and level? I don't need or want a high gloss perfect finish I just want a durable low maintenance finish that won't be to difficult to fix when someone bangs a 2# sinker against it.

    Thanks for any advice
     
  2. kapnD
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    kapnD Senior Member

    I have had good results with a product called Duratec, try a google on it.
     
  3. gonzo
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    gonzo Senior Member

    If you want a flatter more textured finish, spray from a longer distance. First coat enough for cover, let it almost cure and then give it the finish spray with a lot of air pressure and little material coming out.
     
  4. ondarvr
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    ondarvr Senior Member

    Anything you add to make it spray and level better compromises the weathering, water and crack resistance, the more you add the more it degrades the gel coat.

    These clear additives can be a problem because they don't have great UV or water resistance, and adding large amounts of them can change the color, then allow it to yellow much sooner than it normally would. Gel coat relies almost 100% on pigments for UV resistance, by adding a clear product you reduce the pigment loading a great deal.

    They do improve sprayability though, which can help speed up a refinish job.

    You don't need to add anything to it other than a surfacing agent, which help it to spray a little better itself, it will just take a bit longer to sand it down.
     
  5. jimn
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    jimn Junior Member

    Thanks for the replies,

    I was worried about that, It makes perfect sense that the pigment produces most of the UV protection, I bought a gallon of SimTec super clear, Have you ever heard of it? I wasn't excited about adding a product that would put a high gloss on the finish but the fact that it helps it spray and level is appealing, the cost is quite high as well. I don't want a gloss finish and I don't mind a slight stipple. so maybe I should just use straight white gel coat, what would be the max % of styrene monomer you would use to thin?
    I have a HVLP gun with a 2.0 tip
     
  6. ondarvr
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    ondarvr Senior Member

    Adding styrene is almost worse than adding the clear additive, at least in some ways. Styrene loves to turn yellow when exposed to sunlight, so adding it to gel coat increases the chance of premature yellowing. Styrene is a very important component of any polyester product, and does help with the cross linking (cure), but like almost everything in life, to much of a good thing can have negative consequences.

    Some people recommend adding large amount's of various solvents, these do help gel coat to spray better, but they tend to mess up the chemistry and cause long term problems. It's a trade off, easier spraying and sanding for long term weathering and durability, sometimes the trade off makes sense, other times it doesn't.

    If you use surfacing agent (wax dissolved in styrene), 2-4% works OK, This amount shouldn't cause too much of an issue.
     
  7. jimn
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    jimn Junior Member

    Has anyone tried DuraTec at less than the recommended 1:1? like maybe 25%?
     
  8. ondarvr
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    ondarvr Senior Member

    Yes, the less you use the better the weathering and the worse the leveling. Every gel coat will be different though.
     
  9. jimn
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    jimn Junior Member

    what about the lack of surface agent? will it eventually harden enough to sand?
     
  10. ondarvr
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    ondarvr Senior Member

    Probably, I only say that because I have never used that exact product and it will also depend on the exact gel coat you use. Some cure out and become tack free much better than others.
     
  11. jimn
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    jimn Junior Member

    I tried an experiment today on a panel, I thinned a small batch with aprox. 5% styrene and applied two light coats then mixed a small batch with 33% SimTec for the finish, it sprayed fantastic and gave me exactly what I was looking for. I guess I'll find out tomorrow if it cured properly.
    I talked with a supplier this afternoon and he told me boat builders here on the west cost have been using this product for many years and love it, he thinks it's far superior to Duratec. what is the procedure for finishing with PVA?
     
  12. ondarvr
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    ondarvr Senior Member

    Be careful when mixing different products for different layers, or even different ratios of the same product for different layers. Every time you change the mix the color and/or weathering of the product can change, this means if you sand through the top layer into a lower one the color may be different, or it may change color at a different rate leaving an odd blotchy look.

    PVA is applied right after you spray the gel coat, you spray a very light coat over the entire surface. This is easy on a small project, but is a little more difficult when doing an entire hull.
     
  13. jimn
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    jimn Junior Member

    Have you ever heard of using MEK to thin gel coat?
     
  14. ondarvr
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    ondarvr Senior Member

    Yes, it works, has the same problems as everything else though. If any of these ingredients were good to have in gel coat it would be added to start with. There is a huge amount of R&D testing that goes into formulating gel coat, they are made as well as they can be for the amount of money companies and their customers are willing to pay.

    99.99999% of all gel coat used is sprayed onto a mold, a small amount is used to re-spray existing fiberglass products, so that's were all the R&D money is spent. We have made and marketed coatings that far exceed gel coat or other paints for hulls and decks, it could be used in a mold or as a paint, cured tack free with no addition of any other product, held up great below the water and excellent UV and crack resistance.

    The problem was nobody wanted pay anymore for it than they did for their current gel coat so it was discontinued. And the few that would buy a product like this used so little it didn't make it profitable.
     

  15. jimn
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    jimn Junior Member

    There is lot's of product on the market to finish boats and it seem there is even more confusion. The custom boat builders in my area all use gel coat 90% of there builds are for the commercial urchin diver, the hulls are molded traditionally but from the deck up they're custom so they spray it. they say they like the gel coat because it's durable and easy to fix. what do the small boat builders use in pacific north west?
     
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