I had some gelcoat mixed by a local shop. When I asked how many drops of MEKP per ounce I should use he said it can vary. The label on the can states 1.5%. I'm not seeing any guides on mixing at various temperatures and conditions. Can anyone give me some guidance on this? The boat is stored indoors and temps are 80-90F.
Gelcoat Touch up
- Thread starter Project_Mayhem
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Go on line to gelcoat suppliers like Spectrum to confirm how many drops of mepk they recommend. Usually 12 drops per ounce of gelcoat or 1.8% at 77F. That is what target for. In the meantime, you might find this article helpful: Gel Coat Application Guide - How to apply gelcoat correctly (fiberglasssupply.com)
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This video might be helpful -
Around 11:30 he talks about mix ratios. It looks like the link he mentioned in the video is dead now, but if you Google MEK-P catalyst ratios you can find charts. Generally it looks like for those temperatures you’ll want no more, and maybe less.
Edit to add: It looks like the Spectrum chart and some other charts have relatively high concentrations for colored gelcoat. Always follow the manufacturer recommendations if you can find them. You could do a test batch to make sure.
Around 11:30 he talks about mix ratios. It looks like the link he mentioned in the video is dead now, but if you Google MEK-P catalyst ratios you can find charts. Generally it looks like for those temperatures you’ll want no more, and maybe less.
Edit to add: It looks like the Spectrum chart and some other charts have relatively high concentrations for colored gelcoat. Always follow the manufacturer recommendations if you can find them. You could do a test batch to make sure.
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Thickener or catalyst? I don’t think the catalyst should affect the color. The procedures I’ve seen for color matching involve mixing pigments to get the shade right, then only catalyzing it once the match is perfect. If you mean thickener I think it’s unusual to thicken gelcoat. You could thicken regular polyester as a substrate, then overcoat that with the neat gelcoat.
Mepk catalyst will not alter gelcoat color.
Are you talking about cutting Topcoat deck paint with converter, reducer and flattener?
Are you talking about cutting Topcoat deck paint with converter, reducer and flattener?
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I've seen a few articles that suggest adding thickener such as 404 or 406 which sounds logical if the repair is on a vertical surface. Is dripping an issue with gelcoat?
Never added thickener to gelcoat. Maybe a quick drying agent. Gelcoat is reatively thick. Just gelcoated a vertical section where I filled a chip and the gelcoat did not run.
Please post photos of where you want to apply gelcoat.
Please post photos of where you want to apply gelcoat.
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I forgot to grab a before shot but picture an oscillating tool going through the deck creating a jagged 1.5" line. I added 12 drops to an ounce of gelcoat. Mixed it up and then applied it with a resin syringe. An hour later it was still liquid but I'm happy to say that it had hardened enough overnight that I could sand it. It's far from perfect but it was much much easier to do this than I had expected
Thank you for the baseline of 12 drops. That was key to getting this project started. I was reading an article that stated that more hardener could be added to speed up cure times. It was humid and temps were upper 70's to low 80's at the time.
"TotalBoat gelcoat without wax has the same cure time as gelcoat with wax.The gel time (similar to working time) is 8-12 minutes at 77°F, when 2% MEKP is added. Warmer conditions, or increasing the percentage of MEKP, will shorten the gel time. Cooler conditions, or using less catalyst, will extend the working time."
https://support.jamestowndistributo...me-for-TotalBoat-Gelcoat-with-or-without-wax-
Correct - that flexibility is true of polyester resin in general, within limits. Note that it is not true of epoxy. For epoxy the chemical reaction relies on the appropriate mixture, and trying to vary the hardener amount will lead to improper curing and/or reduced strength.