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Paint finish problems using Humbrol matt enamel 82 (lining orange) sprayed via Iwata RG3L


Jimlad

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Hello all,

 

Can anyone suggest what I might be missing here, I'm spraying a polyurethane model which I've cast myself using Humbrol matt enamel 82 (lining orange) via an Iwata RG3L gun with a 1mm tip. Air pressure is approx 30 psi at the gun and the recommended working PSI is around 35. The model has lots of large flat areas and is approximately A4 size and 75mm deep.  No primer and no release agents were used in the mould. I'm aware that spraying to far away results in paint drying too quick and this can leave a furry suede like result, so I'm spraying from approximately 3 inches away, I'm not getting any runs. However I still have a furry surface which isn't entirely even, with some areas looking more furry than others. My suspicion is that I'm not consistently or properly diluting the paint with Humbrol thinners, sometimes I've diluted it in the spray gun cup by eye, (approx 1 to 1) and  sometimes separately and not always to the same ratio's. The model has been repaired and the base plastic colour requires a lot of paint to cover up these repairs, so I'm wondering also whether there's just too much paint on it. I'm trying to put just enough on (in between drying intervals) to just cover these discrepancies. Finally, do you have any thoughts on what to do next, I was thinking of very lightly attempting to de-nib / de-fur it with high grit abrasive? Sorry for the long tedious post.

 

 

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Firstly your equipment and set up is more geared towards car repairs than model painting - most of us will use something more like 0.2mm up to 0.5mm needles and nozzles for large areas. Similarly, 30psi is savage for models and usually there would be no reason when using oil based paints to venture much above 15psi - but your equipment is out with the range that our usual guidance applies to.

 

I'd start with querying your paint mixing prior to use. How did you ensure the paint itself was homogeneous before thinning? Lots of people just wobble the tin around for a few seconds and that does nothing but coat the inside of the lid. They need stirred well, and the best way to do it is with an inexpensive electric paint stirrer to redistribute the pigment, and more importantly, the pigment extenders, uniformly about the liquid binder. All paints are solids suspended in a liquid binder so the important stuff including pigment extenders which enhance the structure and characteristics of the paint will settle out to the bottom over time.

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I would also point out many modellers struggle with yellow red or orange paints.  The pigment is often very thin and I find it's virtually essential to have a nice solid white, buff or pink base coat before spraying the final colour.

 

Hope this helps.

Will

 

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Thanks for the responses, appreciated. The equipment choice was inspired by Paul Budzik's youtube channel 'Scale Model Workshop' and this video here discusses the rationale behind this particular gun set-up. I also have a smaller traditional airbrush for smaller models and I typically only use both guns for base coats. The paint stirrer now seems like a good idea and I'll look into getting hold of one, although I also have a lab mixer so might be time to wheel that out. I use a pipette to add paint and thinners to either the gun cup or a shot glass, in a fairly makeshift manner and then I'd give it a wiggle with a coffee stirrer or tongue depressor until it looked about right (milky). This will be the first habit I'll need to change - I had an image in my head that the thinners would evaporate off and things would even out, it's clearly not as simple as that.  I'd typically run out of paint and then mix up another batch - probably at different ratio's.

 

I did wonder about the pigment/paint thing and it seems that there's also a slight variation in shades across different tins. In terms of the white base coat I've experimented with loads of car body primers and model making primers (often more suited to typical model making polystyrene plastics than PU) and I couldn't find one that was any better than just straight Humbrol enamel. Humbrol do a grey paint called 'primer' however it's just grey paint and has no particular attributes other than colour which would differentiate it. With that in mind I thought why not just use the top coat as the primer or base coat and apply it lightly at first. If I used white for instance as a base coat because I wanted it to show through slightly to give a brighter orange top coat I'd need to get the opacity very even across the whole top surface which is quite tricky on a larger model. Perhaps though another reason to use a different colour base coat is to be able to easily see where the top coat is evenly sprayed, not sure but opinions welcome, however in this case I needed to match the colour of a previous work. 

 

Thanks again.

 

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