help with paint problem

First, welcome to the boards!  There's nary a question out there that someone here can't answer.

Now, on to your specific problem.  It could be a few things, so I'll throw out what comes to mind.

1) Tamiya acrylics don't like to be brushed on - especially multiple coats.  Unless you give the first coat plenty of time to dry (48hrs), the second coat will tend to roll up the first when applied.  Even if you're overlapping, the portion that's overlapping will roll up.  Tamiya acrlyics (when not properly thinned) skin over fairly quickly.  And what's happening is the brush is pulling up the paint that has skinned over but not dried.  It's a real pain in the butt.  Try thinning the paint in a small cup first about 2:1 (paint:thinner) or dipping you brush in thinner, drying some of it off and then in the paint.

2) If this is happening on bare plastics, there could be mold release agents or oils from the plastic itself on the surface.  Did you spray down any primer or wash the model in warm soapy water first?

I'm sure you'll get better answers from more knowledgeable people, but those should be somethings to start looking at.

-Fred

At first I thought it was the paint (Tamiya acrylic) but now they all seem to be doing it. A few days ago this problem did not exist - paint went on smoothly, no problem. I used thinners to clean the brushes and since then, my problem.

There's the problem. You clean Tamiya acrylics with soap (or detergent) and water, Windex, or Simple Green followed by a water rinse. You can also use isopropyl alcohol (90%), which is also the best thing other than Tamiya thinner for thinning and reducing Tamiya acrylics.

Mixing even small amounts of solvent-type thinners (paint thinner, mineral spirits, naptha, lacquer thinner, etc.) with acrylics permanently ruins the acrylic paint. Sorry, but the clumped paint is history—just clean out and save the bottles.

Triarius wrote:

At first I thought it was the paint (Tamiya acrylic) but now they all seem to be doing it. A few days ago this problem did not exist - paint went on smoothly, no problem. I used thinners to clean the brushes and since then, my problem. There's the problem. You clean Tamiya acrylics with soap (or detergent) and water, Windex, or Simple Green followed by a water rinse. You can also use isopropyl alcohol (90%), which is also the best thing other than Tamiya thinner for thinning and reducing Tamiya acrylics. Mixing even small amounts of solvent-type thinners (paint thinner, mineral spirits, naptha, lacquer thinner, etc.) with acrylics permanently ruins the acrylic paint. Sorry, but the clumped paint is history—just clean out and save the bottles.

Well, in all fairness, it was  never mentioned the type of thinner that was used.  Tamiya has a proprietary acrylic thinner (X-20A - basically denatured alcohol), so we can't automatically assume that was the issue. 

But if he did use something other than either of those, then yes, that could definitely be a cause of the problem.

-Fred

Fred, I thought it a reasonable assumption, since the description of what the paint was doing is "classic" solvent-binder incompatibility. Take some Tamiya acrylic, add paint thinner, stir, let sit=goo. Some lacquer thinners produce even more spectacular results. 

Triarius wrote:

Fred, I thought it a reasonable assumption, since the description of what the paint was doing is "classic" solvent-binder incompatibility. Take some Tamiya acrylic, add paint thinner, stir, let sit=goo. Some lacquer thinners produce even more spectacular results.

Hey Ross,

No, you're right, it is a completely reasonable assumption.  Honestly, it's the first thing that popped into my mind as well.  But after re-reading the post, I decided to give him the benifit of the doubt.  But, you never know...

-Fred

Thanks for the welcome, guys

The penny kinda dropped just after I posted - I've always only used enamels, acrylic is something new... I noticed the thinners just hardened the acrylic paint when I tried to clean the brush too.

As for throwing out the acrylic - no problem! I'm sticking to enamels! I actually bought the bottle thinking it was just a bigger bottle of enamel (I've got a pile of freshly bought models and I thought I would need a larger bottle). If I learned something, it's to READ THE SMALL PRINT... 

thanks again, you guys are very helpfull 

 And on Tamiya bottles, the print is very small…and most of it Hirugana…

You're welcome! 

Righto, new problem...

I've ditched the acrylics and applied enamel (3 tone camouflage). Problem is, the shade of grey I applied turns about a million shades darker once dry... It just looks all wrong!

So I decided to strip the paint and start again. I've wrapped the parts in toilet tissue and soaked them in brake fluid, which has totally and brilliantly removed all the paint - except the problem grey... It won't budge. It's Tamiya XF-25 enamel. Any ideas? It has been soaking for a few hours now - should I just leave it a while longer? And, can I apply brake fluid to the canopy glass?

Some paints are much more resistant to brake fluid than others. Let it soak for 24 hour, then use gentle  scrubbing with a soft toothbrush.

Yes, you can soak the clear parts, too.