Airbrushing decanted primer issue

[Paolo_F1]

First of all I wish you merry Christmas and happy new year.
And now let's go to the problem.
I made a test airbrushing some decanted Tamiya white primer on some spare parts to see how it comes instead of spraying it out directly from the can. Well, airbrushing I got an everything but smooth surface with a sort of rough – textured finishing that I had to sand off to fix , while spraying from the can I got a quite good job. Did you ever experienced that? I decanted the primer as usual then I de-gassed it out with a toothpick and I thinned it a little (lacquer thinner), nevertheless I didn’t got what I was expecting for. What’s the issue in your opinion? I’m thinking that airbrushing is far better than spraying from a can, but not this time.
I airbrushed some thin hands with no good result, is it perhaps better to go for a wet coat as for gloss paint? It sound me odd, and I didn’t try it, but preferred to ask you guys, instead of wasting more primer in testing . Any ideas?

[freakray]

What type of thinner did you use?

What was the distance you were airbrushing from?

You may have a reaction between the primer and thinner if you used a thinner which is not compatible with Tamiya sprays.
You may have been spraying from too far away which can result in orange peel due to the solvent evaporating before the paint reaches the surface.

[MPWR]

What Ray sed (kinda).

Thin it with Tamiya lacquer thinner for best results. When airbrushing lacquers, often best results will be had using a considerable amount of reducer/thinner. This could very well solve your texture issue- just add a bit more thinner. It will help the issue of the primer partially drying in the spray stream and 'bumping up' as you apply it.

And if the thinner you're using is incompatable with Tamiya sprays, orange peel is just one of the horrors you could face.

[935k3]

Turn down the air presssure and spray closer. The airbrush atomizes the paint into a finer mist which dries faster, the higher the pressure the dryer the paint comes out. The paint drying too quickly causes the roughness. As good as that primer is out of the can I wouldn't even bother with the mess of decanting and airbrushing.

[Paolo_F1]

Thanks a lot for your help.

freakray, I used Tamiya lacquer thinner airbrushing from the usual distance, about 10-12 cm for small parts. I'm going this way since many years with very good result with enamel paint. Have I to be closer with lacquer?

MPWR, what's the better paint/thinner ratio for lacquer? I noticed that just decanted primer is rather diluted but I add about 20% of thinner, have I to add more?

935K3, I sprayied at about 1,8 psi, have I to turn it down?

[MPWR]

Originally Posted by Paolo_F1

MPWR, what's the better paint/thinner ratio for lacquer? I noticed that just decanted primer is rather diluted but I add about 20% of thinner, have I to add more?

There is really no way to accurately mix by ratio. Especially when spraying decanted paint- the decanting process will remove a variable amount of solvents from the paint, so no decanted batch is likely to be the same as another.

That said, you can often put in a surprising amount of reducer into lacquer. Lacquer will usually airbrush best with the most reducer and the least pressure possible. Add thinner to just before the point that the paint will pool/run as you spray, and reduce the pressure to just above the point where it won't spray. Obviously these are hard things to judge except by test spraying and experience, but I usually spray at between 15 and 20 psi, and I will often add 50% or more reducer. Spray it on in many light coats to avoid runs, but it can go on very smooth this way.

[Paolo_F1]

Originally Posted by MPWR

There is really no way to accurately mix by ratio. Especially when spraying decanted paint- the decanting process will remove a variable amount of solvents from the paint, so no decanted batch is likely to be the same as another.
That said, you can often put in a surprising amount of reducer into lacquer. Lacquer will usually airbrush best with the most reducer and the least pressure possible. Add thinner to just before the point that the paint will pool/run as you spray, and reduce the pressure to just above the point where it won't spray. Obviously these are hard things to judge except by test spraying and experience, but I usually spray at between 15 and 20 psi, and I will often add 50% or more reducer. Spray it on in many light coats to avoid runs, but it can go on very smooth this way.

Ok, as I'm guessing my trouble was due to a thinning error, I added too little reducer, now I'll try with more. I'm very experienced with enamel, but this was my first approach with lacquer, and decanted lacquer seems even more hard to manage than standard ones because of the variable amount of solvent evaporating while decanting them. Airbrushing with too little thinned paint means that paint is almost dry when it hits parts and this was for sure what happened to me, however I'll test your tips and I'm sure that with some more experience and practice I'll match the goal.

[MPWR]

'Error' makes it sound like a fault- it's porbably not so much something you did wrong as something you can do better.

Lacquers are a bit different then enamels or acrylics in that you can spray them much 'wetter' than other paints (using much more reducer). So you can build it up in light coats with almost no surface texture. You're completely right that too little thinner will allow the paint to partially dry in the spray stream, building up a bumpy texture. Spraying with plenty of reducer will eliminate this, and will even let the paint 'level' a bit on the surface it's sprayed on. You just have to control for pooling and runs by making your application coats light (no 'wet' coats!!).

One additional problem you might run into is that a very reduced (thinner rich) mixture of primer may allow the thinner to attack the bare plastic. This will often show as mold lines etching themselves into the plastic after they've been sanded off. If this happens, you'll have to spray the primer with less reducer, and accept that you will have to build up a thickish, possibly textured layer to protect the plastic first. But once you have this barrier, you can gently sand out the texture and spray additional well reduced layers to work up a perfect base for overpainting.

[Paolo_F1]

Thanks a lot MPWR for your great suggestions, I'm surely going to apply your tips starting from next airbrushing session. I'm sure that so doing everything will'go smooth and in the right way.
Ciao