Motorsport Composite Fundamentals: Spray Application - Surface Painter

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Spray Application - Surface Painter

05.15

00:00	In this module we'll look at spraying surface primers onto our patterns, specifically continuing with our CRX fender examples.
00:07	This will give us a better look at not only spray application of primers that will be transferable to other coatings, but also take us one step closer to some composite fenders.
00:17	Recalling from a previous module, we've already completed some bodywork on these fenders, widening the arch and using some body filler to achieve a smooth surface.
00:26	It's important that the surface is coated in a compound that'll be compatible with the other release agents, gel coats, and resins we use when pulling a mold from the fender.
00:36	We'll use a polyester primer called Duratect, which is designed for composite patterns.
00:41	This is a high build primer to fill any irregularities in the surface and has a low porosity, so anything that we apply to the surface next won't soak into it like it would with exposed body filler.
00:52	We'll specifically use the high gloss surface primer variant rather than the easy sanding alternative, because it allows us to polish to a higher surface finish.
01:01	The finish of the pattern is transferred to the mold and then to the part, and although we'll sand and polish at each step, it helps reduce the amount of work if we start with the best surface possible.
01:13	200ml of Duratect primer is catalyzed at 2% or 4ml of MEKP.
01:19	There are a few important things to be aware of here that'll also be important when catalyzing our resins and gel coats as we progress through the practical skills section.
01:29	One is that MEKP contains peroxide, and if we get this in our eyes, it's not just going to hurt, but it'll likely lead to some irreparable damage.
01:37	Make sure you're wearing eye protection, but we'd also recommend squeezing the dispenser bottle to fill the flute with it angled away to avoid it squirting in your face by accident.
01:47	The other thing to consider is the retention of the catalyst in the flute.
01:51	This means if we measure out 4ml in the flute, that doesn't necessarily mean we'll get exactly 4ml when we pour it out.
01:59	In our case we'll actually get about half a ml retained in the flute, so only 3.5ml is poured out.
02:06	We're generally aiming for between 1.5 and 2%, or sometimes up to 3% catalyst.
02:12	For larger quantities like 8ml, this won't make much practical difference, but for smaller amounts like 4ml or under, it can start to have an impact, and we should overfill the flute by half a ml or so.
02:25	With our catalyst added to the Duratec primer in a graduated container, it can be mixed thoroughly before being loaded into the cup of the spray gun.
02:33	We're using a large 3mm nozzle for our spray gun, which is suitable for heavier coatings like this primer.
02:40	Just before painting, we'll give the parts a final wipe down with isopropyl alcohol using a lint free cloth.
02:46	Before painting it's also important to ensure that we have the correct PPE, nitrile or latex gloves, coveralls and a respirator in this case.
02:54	If we have access to a painting booth with proper ventilation, then that's ideal but not necessary.
03:00	And even though a primer like this has little overspray, we still do need to be careful about what we're painting around.
03:06	The primer is sprayed onto the surface in an even coating, ensuring full coverage but not excessive enough to cause runs.
03:13	Painting is one of those skills that takes time and experience to develop, so don't be too hard on yourself if it's your first time.
03:20	Focus on smooth, consistent movements from about 300mm or just over a foot away.
03:26	The first coat doesn't have to be perfect as it'll be followed by a second coat.
03:30	We'll allow 30 minutes or so for the first coat to dry before applying the second coat.
03:35	The aim is to get a thickness of about 0.1mm or 0.005 of an inch for each coat.
03:41	This can be measured with a wet film thickness gauge, which when placed on a flat surface of the part, the number of teeth touching the film indicates the thickness.
03:50	These gauges are relatively cheap, so I'd recommend picking one up as it's difficult to tell just by looking.
03:56	However, over time and with experience, you'll get a feel for what looks right.
04:00	After the second coat is applied, it should be left to dry for 2-4 hours before sanding.
04:06	But this of course depends on the thickness of the coats and the ambient conditions.
04:11	In reality, the longer the better.
04:13	We've primed the fenders with two coats in the morning and then we'll leave them for a few hours and even bake them using a simple heater under a drop sheet tent for an hour or two.
04:22	The next step is surface finishing and sanding, cutting and polishing, which we'll cover in the next module.
04:28	So, for now, let's summarise what we've just done.
04:31	Primers are required to seal porous surfaces so they don't absorb any products that we apply to them in the following steps.
04:38	But they also help fill irregularities, providing some material we can cut and polish for a better surface finish.
04:44	For our CR-X fenders, we've used a Duratec polyester based primer designed specifically for pattern coating.
04:50	This is mixed with an MEKP catalyst and then loaded into a spray gun with a large 3mm nozzle.
04:56	Two coats were applied with 30 minutes of drying time between and a minimum of 2 hours curing time afterwards.
05:02	The aim is to achieve full coverage with no runs and a target thickness of 0.1mm for each coat that can be measured with a film thickness gauge.