Gelcoat not fully hardened

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Gelcoat not fully hardened

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LaxFriedrichs	LaxFriedrichs posted 12 Years Ago HOT Topic Details
Group: Forum Members Posts: 58, Visits: 450	I started a second mould (Unimould system) a few days ago, and the gelcoat is not hardening as it did the first time. The second coat's surface area seems to be 95+% hardened, however there are little patches where it hasn't. In these places the gelcoat is no longer a shiny 'gooey' fluid, it's matte and some what pliable. Is there any way of recovering this? Tomorrow is going to peak at 27 Deg C, could I put it in the sun and use the exotherm of the coupling coat and tooling resin coat to harden it?
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Matt (Staff)	Matt (Staff) posted 12 Years Ago HOT Post Details
Group: Forum Members Posts: 680, Visits: 1.9K	Hi, It sounds like it's just under-cured (at this point). This is most likely to be a result of incomplete mixing of the MEKP catalyst into the gelcoat but I'd have to see exactly the location of these undercured areas in order to see whether they're consistant with this cause. If the gelcoat that's not fully cured is feeling a bit rubbery and part cured and you've already got a first layer of gelcoat underneath it (providing a hard surface for the mould) then I think I would take the chance and go ahead with the coupling layers and backing layers. If you've got 27'C ambient plus you run a decent catalyst level (but don't overdo it on the catalyst for the tooling resin otherwise you'll run out of time for the layup!) then I hope and expect there's a good chance that the exotherm from the main reinforcement will cure finish the cure off but I can't guarantee it. The only worrying thing is that it's not cured after a couple of days which might mean that it's 'stalled' altogether and won't get finished off by the exotherm from the reaction. However, I think I'd be tempted to give it a go! If you don't want to risk it then the easiest method of removing the gelcoat from the mould is to put a single layer of Chopped Strand Mat and standard GP polyester laminating resin on, wait for it to cure and then pull the whole lot out before starting your gelcoating again. I hope this helps, Best regards, Matt Matt Statham Easy Composites / Carbon Mods - Technical Sales Tags catalyst curing gelcoat not problem
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LaxFriedrichs	LaxFriedrichs posted 12 Years Ago HOT Post Details
Group: Forum Members Posts: 58, Visits: 450	Thanks Matt - I'll give it a go! For completeness, I'll post some photos tomorrow. Out of interest, does the gelcoat's effectiveness decay over time or with time after the lid seal is removed. My project required two moulds, using half of the unimould kit on each mould, and the first mould was made about a month ago.
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carboncactus	carboncactus posted 12 Years Ago HOT Post Details
Group: Forum Members Posts: 243, Visits: 1K	Is the rubberiness around the edges? It tends to be as this is where oxygen can get to it, from the sides. Also, is the rubberiness in concave areas? Styrene is heavier than ambient air and will pool in concave areas. Turn the mould upside down for a couple of hours to drain it. After that I would just carry on and laminate. Edited 12 Years Ago by carboncactus
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LaxFriedrichs	LaxFriedrichs posted 12 Years Ago HOT Post Details
Group: Forum Members Posts: 58, Visits: 450	Thanks for getting back to me, CC. The rubberiness is in concave regions. Also there are little tiny blobs ( rad ~2mm) around the edges. I have already completely the coupling coat, which after 3 hours is rock hard ( 2% MEKP and stored in a mini greenhouse). I'll remember the trick of turning over the mould for next time.
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LaxFriedrichs	LaxFriedrichs posted 12 Years Ago HOT Post Details
Group: Forum Members Posts: 58, Visits: 450	UPDATE: I pulled the mould at the weekend. It looked like the 1st gelcoat layer had not fully hardened, due to the alligatoring and bubble like cavities. Fortunately, the distortion on the surface wasn't terribly deep and was not over all of it. Strangely, any surface in contact with the easy release tape was perfect. So I've sanded down the peaks, and filled the deeper cavities with gelcoat. Again it's fortunate that the tolerance on this part is not a great issue... Below Figure show two moulds taken from two different sides of my pattern. Bottom image is a reflection for comparison purposes. TOP - Mould #1 - just needed some finer grades of wet & dry to finish. BOTTOM - Mould #2 - Rough sand of peaks, and cavities are gelcoated over. Much work to be done!
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