"rough" paint finish after airbrushing problem

Plum 1030,
I think you nailed it. My settings and results are the same as what you describe and I only ever have this problem if I try to build coverage too quickly. Although Tamiya is my favourite paint to spray I find it is quite transparent when thinned to the correct consistency. A little drying time between the build up coats has helped this problem for me, just to let the previous layer harden a little. The temptation for me is to quickly just spray light coat over light coat, to overcome this transparency but I have a theory (look out!) that once a certain thickness of paint builds up which is still soft it actually then gets damaged by the next light coat a bit like tiny hail stones hitting the soft paint surface and roughing it up, once this point is reached the rot has set in and the paint surface begins to look powdery and uneven. My way of stopping this is to just SLOW DOWN and after a couple of light coats allow some hardening time before continuing. This is just my crazy idea of whats going on but I hope it helps a little.

Cheers...Snowy.

Polly Scale recommends a 60/40 paint / thinner ratio. I use Polly scale most of the time and this is the ratio I use. Generally, I shoot at about 15psi, but your actual psi at the nozzle can be different than at the gauge, depending on hose length, type of hose, water traps, etc. I waste a lot of paint just trying to dial in my airbrush each time I paint before any ever hits my model. Variations in temperature, humidity, barometric pressure and paint / thinner ratio can all effect how your airbrush will behave.

I thin to the ratios you use but I paint no more than 4 inches from my subject and never more than 15 psi. Then I do minimal paint flow. Spraying close keeps the paint from drying before it hits the model and low pressure keeps the pooling from happening. I then do many light coats of paint and the finish is perfectly smooth. Many coats takes time but the results are worth it.

PantherLehr hi,
i've had that problem too, but luckily it's not too noticeable on my group-build panther; definitely more of a problem for me with aircraft.
leopold, thanks for the heads up, but already use tamiya thinners (either with their paint or polly scale acrylic), and seem to get the problem intermittently, so what do you think i'm doing wrong?
i use approx 25psi and a fairly thick paint mixture (30% thinners max[:0])...is this what's causing my problem?
regards,
nick

i'll get one of the small bottles of tamiya thinner and give it a try , thanks

edit. its not dust , the entire model is like this a few minutes after its painted and when i'm not working on it i got cake containers to put it in

Your intuition is correct. Your paint is drying before it hits the model. The effect you are describing is called dry-spray. If you are using straight Isopropyl alcohol, it is evaporating too soon. The commercial airbrush thinners use solvents like glycol ethers to slow down the evaporation rate. Your paint is thinned enough, I actually use a 60% paint to 40% thinner ratio. Your air pressure could be increased to about 25 lbs and back-off on the paint flow, but I'm not sure that will help. I would drop the bucks for some Tamiya thinner. You could try mixing some water with the IPA, but as I recall, Tamiya paints don't spray well with this mixture.

could it be dust settling on the surface of the paint? i have had that happen to me also, after painting i just stuck the object in a tupperware bowl and put the lid on and problem solved. hope that helps in some way