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MarkMK
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Completely normal given the relatively large diameter nozzle (FN6?) and an 'orange peel' surface is fine, as long as you've not got too many large-ish lumps that might serve to distort the fabric once infused. If so, just smooth these down a bit with some coarse paper. You might find that warming the gel coat a little prior to mixing-in the catalyst will leave a slightly smoother finish, but be mindful of the gel 'going off' quickly if the spraying takes more than 10 mins or so. The GC50 is quite thin already, so unless it's below 15 degrees C where you're working, it should still spray on okay The cup gun is not such a precise instrument, but as long as you're spraying with a decent pressure it you should be able to get an even enough coating with a little practice.
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8900120d
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Hi, I’ve got a g100 spray cup gun, and I tried it out for the first time. I’ve sprayed some gc50 onto my mould, and let it set for around 12h. However it looks extremely bumpy/dotty, almost like you can tell it’s been sprayed on, is this normal?
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MarkMK
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I should have said 'relatively' small, perhaps. I currently get by with a 25L one, although a 50L capacity would work much better for sure and mean not having to pause quite so much for the pressure to build-up again.
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oekmont
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One thing: a small compressor and the cup gun...
The gelcoat gun needs high volume airflow. It should be more than 50L tank and more than 400L/min. At least that's what's my experience.
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MarkMK
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As mentioned previously, I think it's worth investing some time into getting to the bottom of the initial pin-hole problem. With a good technique, you should be able to get parts with near perfect surface cosmetics. If you're envelope bagging, then have a close look at the mould surface, but this should be quite noticeable if there are lumps and bumps transferring to your finished parts Bear in mind that the GC50 is best applied using the G100 gel-coat cup gun. It might be prone to fish-eyeing if brush applied and getting an even application that won't slightly distort the cosmetic look of your parts might be tricky. The GC50 is great stuff and gives a nice polish-able surface coating, with the flexibility to use spray-tacks more reliably, but investing in a small compressor and the cup gun is probably the way to go if cosmetics are highly important When using the XCR coating resin, it's viscosity can lead to lots of air being trapped in it during mixing, so allowing it time to de-gas prior to application can reduce the chance of bubbles popping on the surface and curing to leave craters. Also, it's a good idea to quickly cover parts after coating, to limit the chance that dust particles will settle on it and leave nibs that will result in small craters once sanded. Addressing the cause of the defects in your parts will likely be of most benefit to you and it's likely something simple that you need to change or repair
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8900120d
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Thanks for the replies. I’ve ordered some gc50 to try out. I’m sick and tired of using XCR, every time I put a layer of XCR onto a smooth surface, it cures with craters! What could I be doing wrong?
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oekmont
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No, epoxy compatible polyester gelcoats cure tack free. You have to use sprayglue like you would without gelcoat.
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8900120d
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Thanks a lot, I will try this. Do you normally allow the coat to become tacky first before laying the carbon fibre?
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oekmont
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The one from easy composites is certainly very good. I've used this one lately.
Yes, first you "paint" your mould with the gelcoat, let it cure and the proceed with your infusion setup. Keep in mind that it has to be a special epoxy compatible gelcoat.
However, if you got pinholes now, you will get them with or without gelcoat. But with gelcoat, they will be under the gelcoat, wich makes it eBen worse, as you then will need to sand down the whole gelcoat to fill them.
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8900120d
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+xTue professional way would be to not get pinholes in the first place. Usually restricting the resin flow to slow down the resin speed helps. If you got pinhole free, you could use an inmould coating polyester for a perfect finish and optimal polishing characteristics. A way to get rid of already existing pinholes is clear filler. I used a brand named basco. has to be sprayed onto the part. Fills even medium pinholes and can be sanded down like a dream. This gives the very best finish I can think of. After clearcoating of course. Epoxys like to fisheye a lot. Even the ones made for coating aren't totally free of that. Thank you. I’ve never heard of an inmould coating polyester ? What does that consist of doing? Would I have to coat my mould with the polyester resin before infusing ? Would you recommend any inmould polyester resins?
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