problem hand painting with acrylics

The best acrylic that I have ever brushed with is Polly Scale. It seems to level much better than the other brands that I have used (Tamiya, Testor MM and acryl, Gunze, etc). I don't generally airbrush with Polly Scale since it tends to clog very quickly and I don't like to flush the airbrush every few minutes, but its great for hand brushing. As for the mottled look, could be that the surface is not completely clean. Another possibility is a contaminant in the paint. Hope this helps.

I agree with dnpn that the Polly Scale line and its discontinued cousin, Aeromaster, hand brush better than other brands. I've found that I need to flow it on to get good coverage, and a retarder type product might be helpful to allow it to self-level before it dries. The fact is that the extreme fineness of the pigment in the modern acrylics for modeling makes it difficult to get good brushing, as most of the formulas are optimized for airbrushing. In general, darker colors cover better, and the worst for me are reds and yellows. A cynic might suspect that this is because these are more expensive pigments than some others, and so the producers may skimp for reasons of cost.

Liquitex makes a product called flow-aid that increases the dry times of acrylics.

Add a retarder and every acrylic will become superb for hand-brushing.

Judging by the date of the original post, it's likely the OP would have either found a solution by now or given up...

I never realized that the OP asked 12 years ago.  This must be the FSM record of the longest time between the original post and follow-up posts.

I'm sure it's pretty close to a record.

No real problem, as it may help someone who's having a problem in that area, but there have been plenty of more recent posts on the subject.