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

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Had the same problem half a year ago, problem was not using enough hardener in my case and cold temperatures or a drop in temperatures. 

According to my old books from my time building glass-fibre/polyester boat hulls, the actual content of MEKP itself in the "catalysts" can vary from 40% and up to 80%

Since the MEKP is just a catalyst, the percentage of catalyst to resin is not very critical, but a combination of only half the expected "actual" percentage of MEKP catalyst AND temperatures that are really a bit too low, and the problem will show its ugly alligatored face ...

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Since it was way too cold the first layer didn't cure enough and the second application caused the alligatoring/orange peel look by redissolving the first layer.

20°C is the absolute minimum,  I wouldn't use it at temperatures below that.

I doubt that the concentration of your catalyst is much different than the stuff available in other countries, and dimethylphtalate is a common phlegmatizer used for peroxide catalysts, it won't cause any problems

By the way, forgot to mention, thanks to all for the quick and good answers, its a pleasure to post here !

Unfortunately Dravis is right about the temperature and the issues with the plug surface. 

You really need to be at 20C or above throughout the cure time.

The alligatoring is classic reaction by the gelcoat to a surface it doesnt like. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

MEKP is mots often diluted/thinned with something called  Dimethyl phatalate, since concentrated MEKP is an explosive ...
The locally available MEKP you have is probably diluted much more than the ones Easy Composites normallly use.
Different countries seem to have different laws regarding "deactivating" explosives.

That will almost certainly mean other percentages than "normal" MEKP when added to polyesters as a catalyst.

I think you should try to find out the correct percentage of YOUR catalyst to the "standard Polyesters" that are available locally.

Your "local" MEKP could easily be diluted 5 times more than "standard"

That being said:  17 degrees C. and 13 deg. C.  at night is NOT enough for a proper cure of the EC Unimould system ... You need to have 18 -20 degrees as a minimum.


Perfect example of "alligatoring" in that picture b.t.v. 

I'm pretty sure your "plug" needs a better coating and thicker waxing ... NO rattle can stuff, only 2- component paint, and still weeks curing at temps lower than 20 deg.

Good luck!!


"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)