By Dokomo - 11/20/2014 12:30:17 PM
Hi to all.
It's my first mould using UniMould system. I follow exactly the tutorials and indications for making the mould. For the first step, i have bougth locally an MEKP catalyst ( i have attached the image ). I have applied a thin layer of gelcoat, and 4 hours later, another layer. After that, i have wait to the next day to let it cure, but the surprise was, that the part was totally ruined when i arrived next morning ( i have attached another image ). At that time, it had been drying for about 15h. The gelcoat has reacted with my part ( a motorcycle fuel tank ), producing great wrinkes all around the part. The tank was just finished, laquered and polished with PPG clear coat, and it has been drying for a week before I apply the gelcoat. The room temperature was about 17º in the day, and about 13º overnight. I have made a test yesterday, using 3 small mixes, one in 2%, another in 5% and a extreme one at 10%. The 2% mix, seems to never cure, it has been applied for about 20h right now, and keeps almost fresh. 5% looks nice, it's tacky in the surface and cured in the inside part, and the 10% mix its fully cured. I think the problem has been that the mixture at 2%, has react because it has been applied over the clear coat too much time without cure ( i look at it 6h after the application and it has no wrinkles at all ), producing the wrinkles at the end. The question is, it's safe to work at 5% ? Do you think that the problem it's another one ? Thanks in advance, and sorry about my english.
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By Matt (Staff) - 12/1/2014 4:52:46 PM
Hi Dokomo,
You seem to have a good handle on this now but for what it's worth, we generally advise a catalyst ratio of 3% now for the Uni-Mould Tooling Gelcoat - this is for the exact reason that you're enquiring about - at 2%, even around 20'C - it can be very slow. When it cures slowly, it exposes the materials in the pattern (in your case the PPG coat) to the styrene in the vinylester for a long time which can start to attack the coating. Likewise, if you double-apply the tooling gelcoat over the top of itself you can potentially have the same problem, if the previous layer is under-cured then the styrene in the second layer can attack the first layer. Running at 3% (in typical 20'C conditions) pretty-much eliminates this problem and results are generally better all round. In cooler conditions, slightly higher catalyst ratios might be necessary but ideally 3% at 20'C ambient will be very reliable.
I hope this helps and look forward to hear how you get on.
Matt
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