ready to jump in this week and patch some ugly spots on my C34. I have ground them out as little as possible but the gel coat must be "piled up" approximately 1/16" (maybe slightlly more in places) to look right. Question.....I am worried the gel coat will be too thin to fill up to 1/16". Do you thicken gel coat as you do epoxy to keep it from running? Or will the gel coat be thick enough so as to build up to the level necessary? I am ok with the wet sanding and compounding which will follow....just worried about the "build up". Any help very much appreciated.
Need gelcoat repair advice....Please! (picture)
- Thread starter gwp
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I had a similar problem, they were caused by voids... I dried them out cleaned with acetone then filled them with PC-7 two part epoxy. I waited til' the epoxy cured, (24 hours) then sanded them fair to match the hull. Then I put the gel coat stuff over the epoxy. Has lasted for over 17 years.
Good Luck
Weasel
Good Luck
Weasel
You can use either thickened gelcoat or epoxy and cover with gelcoat. However, I've learned a little about doing this. Matching the gelcoat is not that hard. Wet sand and polish the local area prior to matching the color.
I've found that thickened gelcoat is great but it shrinks all at once about 5 days later. If you sand it flush and spray gelcoat over it the repairs will show up in about a week or so as hollow spots. Wait for a week or two before finishing it, or put a heat lamp and heat it for a few days. Don't get it too hot. I mix Duratec with the gelcoat, add hardener then add the thickener. You can spray gelcoat on it after that.
If you go the epoxy route, make sure it is fully cured. IMHO 24 hours is not long enough. It is my understanding that it is the amines in the epoxy that react with the gelcoat so a full cure, 7 days at 70F is a full cure. I’ve actually wait months before spraying gelcoat over epoxy. I've covered it with primer and waited until fall to spray the gel. That way I know it’s cured. Your mileage may differ.
I've found that thickened gelcoat is great but it shrinks all at once about 5 days later. If you sand it flush and spray gelcoat over it the repairs will show up in about a week or so as hollow spots. Wait for a week or two before finishing it, or put a heat lamp and heat it for a few days. Don't get it too hot. I mix Duratec with the gelcoat, add hardener then add the thickener. You can spray gelcoat on it after that.
If you go the epoxy route, make sure it is fully cured. IMHO 24 hours is not long enough. It is my understanding that it is the amines in the epoxy that react with the gelcoat so a full cure, 7 days at 70F is a full cure. I’ve actually wait months before spraying gelcoat over epoxy. I've covered it with primer and waited until fall to spray the gel. That way I know it’s cured. Your mileage may differ.
I don’t think epoxy should be used.:naughty: Unless it is the final product applied and then it cannot be polished. Some basic truths epoxy can be used with certainty over polyester however the reverse is not true. Cabosil will work as a thickening agent but when you sand it it will be pores. So my suggestion would be to prep with a good sanding using 120grit ,clean with acetone and apply gel coat thickened with cabosil but only to a point that will leave it below your finished level sand clean and apply your finial coats with out the cabosil also topcoats should have styrene to set the product. Sand with 600 wet or dry then compound. The tricky part is blending old and new and that is up to the artist/mechanic.
Good luck
Bill
Good luck
Bill
Please also consider joining us at our C34 Message Board: http://c34.org/bbs/index.php/board,11.0.html
You might want to check out the CRITICAL UPGRADES topic which is a sticky on that board.
You might want to check out the CRITICAL UPGRADES topic which is a sticky on that board.
I've used Marine-Tex for some above water drill and fill projects. Works great for me. It's a 2 part thing (not sure off the top of my head if it's epoxy based or not) Can you use it below the water line? If so, you could fair it out, like spackling, let it cure, sand it flush, then use gel-coat.
Actually that is not true. West Systems has addressed this in a white paper article, that polyester can't be used over epoxy. Considering I have done this many times, and never once had an ounce of issues, I know it to not be true. Gelcoat sticks just fine to properly prepped epoxy. If you feel like using polyester that will work too, and will cure faster.
If you read the article you will see that the gelcoat is still bonding at well over 500 PSI or better even when submitted to 100% humidity in a 100F room, for many weeks. In most cases it is bonding at over 1000 PSI.
West Systems Polyester Over Epoxy
"Our test clearly demonstrates that polyester
gelcoat will bond to a properly prepared
WEST SYSTEM® epoxy as well as to a cured
polyester laminate. This test confirms that
polyester gelcoats can be applied over cured
WEST SYSTEM epoxy on repairs below the
waterline."
Yes, you DO NOT want cabosil in the final layer but it does help with the build up layer and prevents crazing. You also do not want micro-baloons as it can bleed through a white gelcoat in time. You can also add Waxsol to the gelcoat or buy your gelcoat pre-waxed. If using only waxed let it kick about 15-20 minutes between coats so the wax will still rise off to the surface for cure. If you let it fully kick off then you'll have to de-wax and sand between coats of gelcoat. You can also use un-waxed gel then use waxed for the final coat.
I prefer to shave the high spots with a sharp edge of a razor blade, sharp chisel or a set of jewelers files. One thing many are not aware of is that the surrounding gelcoat will sand away at a rate that is MUCH faster than the new gelcoat. I have seen many folks patch an area only to then sand through the surrounding area and wind up with a much larger job. This is why I prefer to take down the high spots of the new gel coat with tools before busting out the sand paper.Sand with 600 wet or dry then compound. The tricky part is blending old and new and that is up to the artist/mechanic.
Good luck
Bill
"Our test clearly demonstrates that polyester
gelcoat will bond to a properly prepared
WEST SYSTEM® epoxy as well as to a cured
polyester laminate. This test confirms that
polyester gelcoats can be applied over cured
WEST SYSTEM epoxy on repairs below the
waterline."
This is a first time hearing this for me and It is very timely and welcome info as I have a project boat and I’m not to sure what was done before it came to me. Hopefully the PO had this info as well and used west system or comparable epoxy.
And I agree with using other tools on the built up area prior to finish coats although most folks idea of a sharp tool is inadequate for the job and it might do more for frustration and to add damage then to do good.
Thanks
Bill
gelcoat will bond to a properly prepared
WEST SYSTEM® epoxy as well as to a cured
polyester laminate. This test confirms that
polyester gelcoats can be applied over cured
WEST SYSTEM epoxy on repairs below the
waterline."
This is a first time hearing this for me and It is very timely and welcome info as I have a project boat and I’m not to sure what was done before it came to me. Hopefully the PO had this info as well and used west system or comparable epoxy.
And I agree with using other tools on the built up area prior to finish coats although most folks idea of a sharp tool is inadequate for the job and it might do more for frustration and to add damage then to do good.
Thanks
Bill
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