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!

I get this on occasion as well (generally much worse when I use acetone to clean the release agent off the edge of the flange for the bagging tape) - have not worked out the cause for it.

That said, I dont have any release issues using the moulds. I suspect that your release failure was entirely to do with the contamination of the EasyLease, and the reason it was worse on the flanges is because flanges moulded off Correx will tend to have a surface texture that is much easier to bond to than a nicely polished mould surface.

I would suggest putting it down to that, and trying again without changing the process but making sure to not contaminate your release agent. I ALWAYS clean > compound > clean again, using one cloth to apply the mould cleaner and another dry one to wipe it off before it evaporates. After you have cleaned the mould surface, apply a strip of 2" masking tape and peel it off, noting the resistance you feel in doing so. Then after applying your release agent, do the tape test again, and compare how it feels prior to the release agent. If it doesn't feel much different, do 4 more coats of release agent and try again. If it still doesn't feel much different, something is wrong. With a high slip release agent like EasyLease, the tape should come away extremely easily with almost no resistance. 

If you are really worried about it, you could use something like EC's S120 tool sealer on the flanges.

Thanks for your help, interesting that you have had the same. I take it the compound in clean>compound>clean is a polishing compound?

I spoke to EC technical help as well and their thoughts were that the Correx had slightly delaminated early allowing air in contact with the surface, which make sense but I did have the gel coat on for 24 hours before the coupling coat so not sure if it could have delaminated with just the gel-coat? 

Also on further inspection it only has a tack after passing over with the mould cleaner, when dry it is ostensibly hard to the touch so I don't know. Their recommendation was to keep cleaning until stuff stops coming off and is no longer tacky, or apply a bit of heat to try and finalise the cure, and as an alternative if still no luck I could apply wax over the easy-lease on the flanges. After going over with the mould cleaner there is a mottled sort of finish to the gel-coat with completely matte areas and others a bit shinier so I wonder if the matte areas are where the solvent has removed all there is to remove - but that said after a good 10 mins of concentrating on a single area I'm still getting a bit of black on the towel. Only on the application cloth though - nothing comes off on the dry cloth when I wipe off the solvent so it must be a very minor amount.

I did the tape test as you suggested on a small area with just a single coat of easy lease and there was a very noticeable difference so that seems to suggest things are OK. I will do a few more passes with the mould cleaner to get it as good as I can without spending forever on it and stick with the process. I am a bit reluctant to add wax over the easy lease after the issues I had last time though - I really want to avoid destroying another mould as I don't have the time (effort or money!) to do a third!

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

Thanks Warren, I think we may have spoken earlier today.

I'll go over with the heat gun a few times see how if that makes a difference. I was thinking of the tape as a potential fix as well! I may do this just for peace of mind, even if it is a bit time consuming.

Just a question on the wax - can this be any car wax, or might they have additives that will cause issues? Only wax I have knocking around is the G3 Superpaste Wax, which is sort of a hard wax but not quite as it goes very soft immediately when touched. And if it is acceptable, it should be OK as long as it is applied on top of the easy lease?

I would stay away from unknown waxes. Composites can be a super unforgiving process, and they will bite you hard if things aren't right. Chemical incompatibilities is a big one, and there are loads of different chemicals out there - waxes included. While I know Carnauba based waxes are used in both release waxes and car waxes, there is no saying that there aren't other solvents or chemicals in there that will cause issues. Or perhaps a car wax may be too thin and not build enough to function well as a release agent. There are plenty of people who will argue with this and say they have had success using various waxes etc. All things considered, it is a risk. And if you have already binned a mould and this is make or break time, you don't want to be putting your faith in materials that are an unknown variable.

Your problem does sound a bit different to what I have experienced. I've never had patches go dull after cleaning, this does indicate that the surface isn't cured properly. For me, the mould visibly remains exactly the same, but I get some red coming off on the cloth I am using. I would suggest covered these dull areas is going to be a good idea, either with flash tape or with PVA release agent. Get a physical barrier in between, because there is something odd going on. Whatever you use - just keep away from the flange edges where your bagging tape needs to seal. 

Agreed on waxes.  Use a composites intended mould release wax if you go down that route. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks both.

I carried on with the cleaning and some heat and it definitely improves. In some areas none is coming off now and in others it is much less so that is working but I think I'll go with the tape option as there's a bit at stake and it gives peace of mind. If I end up doing a few more parts I may try with PVA or proper wax but I want to get at least one good part to start with. I am going to put down easy-lease first then tape over the top just in case there are any areas where the tape lifts at the edge and resin gets in under it. The flash release tape still seems to have enough stick over the top of the easy-lease to stay down.

Yeah, it does seem clear there's not been a proper cure there for some reason; the main part polished up well and isn't affected by the mould cleaner which is the main thing. I will report back on how it all goes.

From the conversation and the mould images, I guess it is really only related to the flanges
If you can stabilise the flanges and overcoat them with epoxy, possibly even the XCR then you may get a permanent mould to recover costs before creating a new one

As for my projects, yes it is a challange to find the right techniques and materials for a particular job,
yours definetly looks better then my first 2 molds :-) and I'm still learning,  it's part of the fun for me

Just following up on the above. I put down flash/release tape over all the flanges and this worked well, and had no issues. Also helped with releasing as it gave an easy edge to work release tools under.

To be honest, I think I will continue to lay the flash tape down on the flanges for any subsequent attemps as it helped so much with the release of the part, plus it's a bit of extra piece of mind. Thanks for the advice all. Now just have to resolve some trapped air/bridging issues and hopefully will be there!