Hi all,

I have a bit of a head scratcher that I am not sure what to do about. I have made a mould for vacuum infusion, using the uni-mould system with standard Correx fluted signboard to form the flanges. I am now coming to the final cleanup before putting down the Easy Lease release agent, but when I pass over the flange areas where the Correx was with the Easy-lease mould cleaner it constantly picks up something black from the surface (I am presuming the gelcoat as these areas had nothing else on them) and continues to do so over multiple passes.

I can only assume that the mould cleaner is attacking and dissolving the gelcoat, as there is a bit of 'grab' after passing over it, but it only happens in the areas of Correx. There is no issue with the areas on the part itself, or the areas of flashtape covering joins in the Correx. The gelcoat was all done in one go so it is the same ratio mix of catalyst/gel-coat as for the areas that have no issue, therefore it isn't a case of under catalysed areas of gelcoat. It is on all Correx areas, and only Correx areas; adjacent areas on flashtape are fine so that rules out undermixing as well.  The gelcoat had at least 48 hrs curing before demoulding and was catalysed at around 1.5% - plus as the other areas are fine I don't think there have been issues in the process.

Any ideas why this is happening? 

This is the second mould after the first was ruined during demoulding of the carbon infusion. I remember with the first mould cleaning up the Correx areas and getting the same result. At the time I put it down to residue from the black tape covering the flange joins I used (so I made sure to just use flashtape this time), and a conversation with Easy Composites technical support confirmed there shouldn't be any issues with the mould cleaner and the gelcoat so I proceeded.  I had some issues with the Easy-lease release agent where I made a mistake and it got contaminated with an application of wax I had used to get a good shine to the finished mould surface, so I didn't get a good release and some areas of carbon stuck to the mould and vice versa. However, the areas that were worst affected were the flanges where I hadn't applied any wax, just the easy-lease and it had pulled a good deal of the gel coat straight off the mould.

With the gel-coat being air inhibited my thoughts are that the Correx is somehow breathable and has not allowed the gelcoat to harden on the surface both times meaning it still has a tack and has bonded with the epoxy/or interfered with the easy-lease. Surely this can't be the case though as this is the recommended procedure? And if that is the case, what can I do about it? I fear that the I am going to get the same result as the first mould if I proceed...

Any help would be much appreciated!

If after the such a lot of cleaning you are still getting bits on the cloth and heat has had no impact, It could be maybe the gel is just not quite 100% cured.  Its hard to speculate exactly what could be happening.  Perhaps the flanges didn't get as hot during the curing compared to the main part of the mould.  Could be anything like not quite properly mixed gel or some other factor meant it hasn't quite got to 100%.  As always, heat helps cure resins and can sometimes force something to cure a bit better than otherwise so is beneficial.

Hanaldo makes a good point about the surface texture.  Some grades of corex are smooth and glossy, some have an etched surface to help with sign assembly and vinyl adhesion etc.  A rough surface is harder to release from due to mechanical grip - often even with release agents.  Waxes have a high solid content so can fill in some of that with multiple layers.  Or a surface coating works too.  Also as its a flange and is not cosmetically critical, you could use PVA mould release in those areas too.

If things are really bad, a quick temporary fix is to tape over the flanges with a release tape or even polypropylene parcel tape as the resins won't stick to them.  Preferably that would be at the mould making stage rather than onto the mould flanges but it will work on the flanges too. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant