Gelcoat as non-skid on Deck

Discussion in 'Boatbuilding' started by Klink Sanford, Dec 10, 2021.

  1. Rumars
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    Rumars Senior Member

    I was just trying to save him having to carve the pattern in a linoleum sheet. On wax he can simply press the pattern in with a textured roller. The wax can be reused, if it's mangled from demolding just level it with hot air and imprint the pattern again.
     
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  2. Klink Sanford
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    Klink Sanford Junior Member

    In the 12 tests I used PVA on the first 6 and I used wax from there on, on the last 6 tests. The three final tests were on the epoxy deck of the boat and in all of them I used wax additive and it stayed wet for days. Two of those I removed while still wet after 2 days.. The third is still on the boat now like 7 days and it was wet for days and yesterday had 90% of the area hard and 10% rubbery, but not wet anymore.
     
  3. rxcomposite
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    rxcomposite Senior Member

    Have you tried side by side testing? Same mixture of poly with wax and apply it to one polyester surface and one to epoxy surface? Both fully cured, dewaxed, and sanded. That is the only way to test if it is your mixture or the substrate that is at fault.
     
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  4. Klink Sanford
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    Klink Sanford Junior Member

    I applied waxed gelcoat to a 10 year old deck locker board that was made of plywood covered with CSM and gelcoat. I only cleaned it and did not sand it. The gelcoat dried fine and is hard.
     
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  5. Klink Sanford
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    Klink Sanford Junior Member

    That was one of the 12 tests.
     
  6. ondarvr
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    ondarvr Senior Member

    While in general this can work, not all epoxies and gel coats use formulations that are compatible, and it is not possible to test every combination of the two. Then you run into mix ratios that may not leave a substrate fully cured.
     
  7. Klink Sanford
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    Klink Sanford Junior Member

    That's what I kinda thought since people said you could put gelcoat over epoxy but I was not able to do it AND this gelcoat did not harden over shellac/varnish and plywood where the adhesive was exposed. This gelcoat brand must be sensitive. The epoxy floor was 4 years old, the shellac/varnish pine baord 20 years old, and the plywood board with exposed adhesive was 2 years old. The Gelcoat was fresh, a little over 30 days old, it was from Fiberglass Supply Depot. The epoxy was from Raka.
     
  8. Klink Sanford
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    Klink Sanford Junior Member

    I went back and looked at my last test plywood board (12th test) , where I duplicated exactly what I had done on the last unsuccessful test on the epoxy boat deck (Test #11). The 6 dime sized spots on the plywood board that did not dry, still have not dried, now 3 days later, and they have a more cream like color to them, like the gelcoat absorbed something. I easily scraped the gummy gelcoat off on the six small spots and found they are all knots in the plywood. So, the gelcoat will not harden over pine knots.

    Add to that what I wrote about an earlier test, that the gelcoat did not harden over a pine board that had 20 year old shellac or varnish on it.
     
  9. rxcomposite
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    rxcomposite Senior Member

    You must have stumbled into some "sticky" situation here and should give a heads up to builders on applying gelcoat to any surface. Something is inhibiting the gelcoat from curing properly. It is supposed to consume the MEKP to cure properly and at the same time be inhibited from air which contains moisture. Perhaps Ondarvr has some explanation how a gelcoat cannot cure properly.

    I suggested sanding before carrying out the test. That is to remove surface contaminants that might affect gelcoat cure.

    Below is high grade ISO resin laminated over Epon epoxy mold some 20 years ago and was exposed to the elements. The poly resin cured properly. The epoxy mold is still solid as ever but the poly resin is delaminating. Epoxy is supposed to be 1:1 per molecule and bonds to itself well. It should be inert after cure and should not add anything to the poly resin to cause it to cure improperly. But, that is my experience.
     

    Attached Files:

  10. ondarvr
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    ondarvr Senior Member

    Not hardening over knots in wood is common.
     
  11. ondarvr
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    ondarvr Senior Member

    Normal gel coat won't harden over cured methacrylate adhesives and other substrates either.

    I haven't experienced it not curing over epoxy unless the epoxy isn't fully cured. While the longer it sits the more thoroughly cured it should be, time isn't a guarantee that it was actually mixed close enough to the correct ratio to not leave unreacted chemicals that could affect the cure of the polyester.
     
  12. Blueknarr
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    Blueknarr Senior Member

    I have had non-curing gelcoat where acid was splashed.
     
  13. Klink Sanford
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    Klink Sanford Junior Member

    On the first test (1 sq ft) on the actual boat epoxy deck, I sanded with dry 80 grit, vacuumed the dust, and then wiped it with a wet towel, it turned out that what I thought was water that I put on the towel, was vinegar (an acid), so I went back and wipoed the area real well with a water wet rag, and let it dry, then wiped everything with 92% strength Iso propyl alcohol, let it all dry, then applied the gelcoat. 24 hours later it had not dried over the epoxy, so I scraped it off with a metal spatula. It was like a fresh thickened gelcoat (I only used un-thickened gelcoat). Then I wiped it off with paper towels. Then wiped it with green Scotbright and acetone, and finally with a toothbrush to get the little crevices. All that was left was a very light haze which I sanded again with 80 grit.
    Then over the same 1 sq ft spot, I did the test described in an earlier posting: "The third test is still on the boat now like 7 days and it was wet for days and yesterday had 90% of the area hard and 10% rubbery, but not wet anymore".

    Hard to believe that the vinegar would have still been present, even two times after all of the cleaning. What do you think?
     
  14. Blueknarr
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    Blueknarr Senior Member

    It takes a mild base solution to neutralize the acid.
    Wash with a bit of baking soda or a few antacid tablets in water. Then rinse with lots of clean water.
     
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  15. Klink Sanford
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    Klink Sanford Junior Member

    If I have the time and the curiosity, I may do a test elsewhere on the boat to see if the vinegar was the problem but cleaning up the last gelcoat test off the deck was a hassle I don't feel too keen about having to repeat. I had to use acetone, SS wool scrubbing pads, Scotchbrite pads, scrapers and sandpaper to remove all the sticky gummy parts. Attached is what was left that did harden of the 1 sq ft area that I gelcoated over the epoxy deck.

    (P.S. - the wood boards are epoxied on, to later attach the center console to them without drilling into the Boston Whaler foam deck.)
     

    Attached Files:

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