Let's beat a dead horse. Again.

I don't know if this will help, but when I had this problem it was because I was in too big of a hurry.  The paint needs to go on heavy enough to look wet in reflected light, but look dry in a few seconds.  Common advice is to mist it on, but you can overdo this.  It needs to be wet enough for the little droplets to flow together before they dry.  At least that was my experience.  I use ModelMaster enamel thinned 50/50 with lacquer thinner.  Good lighting is important.

Don

Don, what you say makes sense. I watch for the glossy look as I paint but this time it took so much paint to get there that I nearly had runs. I believe that your theory that the paint is drying to fast is correct.

Humbrol is an enamel & thinning it 50/50 with lacquer thinner is causing it to dry too fast.  The velvet is actually paint particles that dried before they  got to the model.  If using lacquer thinner with enamel, I never thin more than 2:1 paint to thinner.  If you want a thinner mix, switch to Mineral Spirits for the thinner.

Regards,  Rick

I just tried again with MM enamel thinner mixed 70/30, paint dried pink. Tried again mixed 50/50 MM thinner, paint dried red but roughness was back though not as bad as before.

I'll make a note to try mineral spirits next time. I've seen way to many lovely, nice and smooth paint jobs to think it's out of reach for me. And so few people ask how to fix it so I have to figure out the trick.

Rick has it spot on.

You didn't say what type of airbrush, gravity fed or siphon. It makes a difference in spraying pressure. For a gravity fed brush,  drop the pressure to ~10 to 15 psi. If that's too low, raise it slightly, but 20 psi is about a maximum. Six inches is also pretty far away, even for coverage coat.

Lose the lacquer thinner! Lacquer thinner is for…lacquers. Use mineral spirits as your reducing solvent for enamels. Thinning ratio will depend on the paint, but the old rule of "consistency of 2% milk is a good guideline.

Ross, I left that out didn't I.

Iwata Rev CR gravity brush. So far I've tried 15-20 psi but nothing lower than 15.
I smoothed the surface and tried again with MM thinner 70/30. Paint dried pink. Weird.
I remixed 50/50, paint dried red but was rough again. I rubbed it smooth and gloss coated the heck out of it. This experiment is over but I've kept a copy of all advice in a file for the next time. As I said, this is an ongoing problem and I know I'll have to deal with it again in the not so distant future.

Mate, have you tried using 1 part Humbrol thinner to 2 parts paint at about 15 psi or your preferred pressure?

I know it sounds like a no-brainer and I don't want to tell you how to suck eggs but when problems strike, for me it's always best practice to go back to the bare bones basics of using the brand's own thinner matched to the paint, etc, etc. I gave up trying to second guess the manufacturer regarding thinner compatibility a long time ago and figured they know more about the paint they make and the thinner best suited than I ever will. Also, I've found Humbrol paints need to be stirred really, really well, and then some!

It sounds simplistic but I've always had least problems when I used Humbrol thinner with Humbrol paint, Tamiya thinner with Tamiya paint.

Cheers,

Snowy.

I am no expert on the subject, but I have had a similar issue ongoing with Tamiya Acrylic, I am hoping I will get better results when I get my hands on their new retarder - as someone said above, although not always necessary I think that using same brand everything is wise.

Do you prime your models?

Although some suggest it isn't really required, I usually prime before painting, this assists in smoothing out fine flaws, gives the colour coat something even to go onto & promotes adhesion - it is just the mindset I have always had - prime, then paint.

However, looking through my built kit's from the last couple of years, one thing stands out like a sore thumb, the two kits which I did not prime way & by far have the better finish in terms of texture. Now I know the obvious conclusion here is that the primer coat on the primed kits was rough to start with, but that was not case, all the primed kits have been done with Mr Surfacer 1200, which was checked for smoothness & sanded / polished as required, leaving a finer / smoother finish than any Tamiya Acrylic has done for me.

This has left me wondering if there is something going on when the colour coat hits the primer, not a typical style paint reaction that you would get regular incompatibility or inadequate drying, but some other sort or reaction between primer & top coat that is preventing a smooth "lay down"?

Triarius - being our resident expert, could you comment on the possibility of this?

I don't have any Humbrol primer, wish I did.
The model was primed prior to painting. Lots of body work under there and needed it to find flaws for fixing and hiding others. The finish was nice and smooth.

I'm one of those far from great airbrushers, but I'll always throw my two cents in.  I agree on the mineral spirits/ paint thinner, 15-20 PSI, and the paint consistency of milk (I think 50/50 is too thin).  Aaron Skinner hits on several of these points in his article in the magazine this month.  Distance from the model and the speed of the pass factor in also.  And as you all have mentioned, the point in space that the paint is drying is the key to this problem.  All these variables factor together. The visual result you want on the model is a wet application that appears to dry very quickly.  Like was mentioned, several passes are better than one heavy coat.  Check out Aaron's article it made some very good points.  Rick

hkshooter:

You might try brush painting a scrap piece of plastic with the paint you are using to see if you get the same results as when you air brush.  Flat paint contains a flattening agent, that makes the paint rough.  I've started using gloss paints with a flat overcoat to achieve the desired results.

Milairjunkie

<snip>

This has left me wondering if there is something going on when the colour coat hits the primer, not a typical style paint reaction that you would get regular incompatibility or inadequate drying, but some other sort or reaction between primer & top coat that is preventing a smooth "lay down"?

Triarius - being our resident expert, could you comment on the possibility of this?

Assuming the primer is fully cured and not susceptible to the solvent in the paint applied to it, there should be no reaction. However, (there's always a "however," isn't there?) it is my understanding that Mr. Surfacer can be reduced with alcohol. Alcohol is the best reducing solvent for Tamiya acrylics, so there is a possibility of it attacking the primer surface, especially if the primer were not fully cured, or still contained a small amount of solvent. There is also a possibility that the primer surface was more sufficiently porous to absorb solvent  from the applied paint, which would definitely cause the results you report. Try applying a sealing color coat, allowing that to cure, then applying normal coats. As I don't use Mr. Surfacer except in dire situations (substandard foreign styrene), I can't experiment to find out what might be going wrong.

While there are other effects that could produce your reported results, encountering them consistently would be highly unusual.

Thanks Ross, I think the next time I have something up to the paint point I will miss the primer again & see how it turns out. Absolutely no doubt in my mind that the Surfacer was cured, so the porosity may be an issue.

Milairjunkie

I am no expert on the subject, but I have had a similar issue ongoing with Tamiya Acrylic, I am hoping I will get better results when I get my hands on their new retarder - as someone said above, although not always necessary I think that using same brand everything is wise.

...

Hey Milairjunkie, where did you hear about he retarder from Tamiya? I've been gradually switching to their acrylics, but have a bugger of a time brush-painting details, touchups etc. I've been told that I'd have better luck with the retarder. For now I keep using Humbrol for details, love the coverage with a brush. (Haven't airbrushed with them in ages though, so I'm not sure I can add anything useful here!)

Vance

I noticed it on their website, the product number is 87114 - here is a direct link;

http://www.tamiya.com/english/products/87114paint_retarder/index.htm

Bee-u-tiful, product # and everything - thanks for that. Now off to the LHS!