Motorsport Composite Fundamentals: Applying Gelcoat

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Applying Gelcoat

04.25

00:00	The gelcoat is the first product we'll be using that will form part of the finished product.
00:05	Specifically the surface layers that will not only help protect the laminate, but provide some material to cut and polish for a smooth finish, and also help to reduce the chance of surface voids.
00:16	That said, gelcoats are an optional step.
00:19	They're not required and are often unused for parts where lightweight is the number one priority.
00:24	They are usually used, however, on body panels for the reasons we just mentioned, and on fiberglass parts to hide the CSM reinforcement, because let's be honest, it doesn't look great.
00:36	We'll be using a clear gelcoat for this example, rather than the typical white or gray for fiberglass parts, solely for the purposes of this course, and being able to see the laminate in the final part.
00:47	This won't make a practical difference to the process.
00:50	The specific gelcoat we're using is Neopro Marine Clear, and it's designed to be sprayed on.
00:56	Spraying would usually be our choice of application.
00:59	It's far more efficient and easier to get a consistent film thickness.
01:03	However, we're going to brush it on again for the purpose of this course, just to show the most accessible and manual approach that anyone could do at home.
01:11	All that we need to do this is our mixing container and some disposable chip brushes.
01:16	It's best to have a large and a small option for different parts of the mold.
01:20	The surface of the mold is ready to go from our last modules, so let's get into it.
01:24	Just like with our tooling gelcoat, we're aiming for about half a millimeter of thickness for each coat, which we'll only do one of.
01:32	We've got less than one square meter of area between our two fenders, so we'll mix up 400 millimeters of gelcoat.
01:40	As usual, we'll catalyze this with MEKP at 2%, so that's just over 8 milliliters in our catalyst dispenser flute, to account for some retention, as we discussed earlier in the course.
01:51	It's also important to fill the flute with it aimed away from our eyes.
01:56	This is mixed thoroughly for one to two minutes, continuously scraping down the sides to ensure it's fully mixed through, and we aren't going to end up with uncatalyzed patches that won't cure.
02:06	When we start painting it onto the surface, we'll generally start in the sharp corners first, and then brush the larger surfaces.
02:14	The typical pot life for these gelcoats is about 20 to 30 minutes with 2% catalyst.
02:19	In the case of our fenders, it's fairly easy to get the job done for both moulds in about 10 minutes, but for larger or more complex parts, time is something we need to keep in mind.
02:30	In extreme cases, we might have to work in stages, mixing a second pot as the first goes off, but this is generally okay, as of course the gelcoat isn't waxed and won't fully cure.
02:40	Again, we're aiming for a smooth even film at half a millimeter thick, which we can measure with a film thickness gauge.
02:47	The tricky areas to achieve the correct thickness are in the deep corners or in the outer edges.
02:53	Too thin and we won't have enough gelcoat to do its job, and cut and polish smooth.
02:58	Too thick and will likely cure unevenly with hot spots when we're laminating, causing the gelcoat to tripe and leading to a rough alligator skin texture on the surface of our parts.
03:08	With that said, we recommend starting with these difficult areas and working to get them the correct thickness without having to worry about the excess gelcoat on the rest of the part interfering.
03:18	After these tight areas are sorted, then it's easier to move on to the more open faces.
03:23	At this stage, we need to allow the gelcoat to cure for at least two hours before backing up with the laminate.
03:29	However, ideally we'd leave it much longer, like overnight, as this is going to reduce the chances of the lamination process causing it to tripe.
03:36	As always, when we're finished, our exothermic resin mixture needs to be disposed of safely.
03:41	Before we move on to backing up our gelcoat with the lamination stage, let's summarize the key points to remember from this module.
03:48	With our release agents applied and cured, the next step is gelcoat.
03:52	We're using a clear polyester gelcoat for this example that's compatible with our mold and lamination materials, and we'll be brushing it on to show the most accessible approach.
04:02	After the gelcoat is mixed thoroughly with MEKP catalyst at 2%, it can be applied to the mold surface to create a smooth even film at 0.5 millimeters thick.
04:12	It's important to avoid too thick a gelcoat layer and not enough cure time, as this will cause issues with the laminate and lead to poor surface finish or mechanical properties.