Brush Painting with Tamiya Acrylics

Retarder definitely does help with being able to brush paint Tamiya, but I still try to do that as little as possible for the same reasons as you found with it.  For doing touchups with it, I have had much better luck by just loading my airbrush with a little bit and just hitting those spots with quick little spurts with my Paasche H and #1 cap/needle turned all the way down to the smallest pattern I can still get paint to flow with.  You get better coverage that way, without the paint going on nearly as thick as it does with a brush, and the sheen stays the same as what is already there because it was applied the same way, with the same additives.  Lately though, I have pretty much been avoiding touchups altogether by just using a more durable paint.

nvm

Wilbur Wright

Tamiya acrylics are notoriously difficult if not impossible to brush paint

Tamiya is like any paint. You have to learn to use it.  I remember brush painting with testors enamels when I was a kid. If I painted over one color with another , the top color would dissolve and mix with the base color. It was not an issue with the paint, rather my technique...

in my experience the retarder will not help.

Interesting.  Thank you for the feedback, Wilbur.

In parallel with my scale modelling, I've been putting together a few small structures for my HO shelf railroad.  I tried brushing the Tamiya acrylics on an interlocking tower, and even using the retarder, I didn't have a lot of success.  Ended up airbrushing it; that worked out fine.

Tamiya acrylics are notoriously difficult if not impossible to brush paint, and in my experience the retarder will not help.  Go back and airbrush those parts as you said.  I use Humbrol enamels to brush paint as they are dead flat. 

All usable Testors MM enamels for military models have been phased out.  I am transitioning to Tamiya acrylic as my #1 and also AK real colors for airbrushing, and Humbrol enamel for brush painting.