cracked paint

What kind of paint and what thinner?

Sounds like an incompatible thinner to the type of paint used.

Paint cracking and leaving a snakeskin-like effect can have a number of causes.

• poor adhesion to the surface, leading to cracking from shrinkage of the paint as it dries. May be caused by surface contaminants (oily residue from your skin etc),  over-thinning of paint (so much that the paint's binder is degraded)
• if a primer coat was used but not allowed to cure fully before overcoating with the top coat, the different layers drying at different rates may cause cracking. Allow the primer coat to cure fully before overpainting. Paint in very light coats and allow to cure before overcoating.
• If the paint was applied too thickly the outer layer may be dry, but may crack due to shrinkage of the inner layer as it dries. Paint in very light coats and allow to cure before overcoating.

In my experience, this sort of cracking happens more frequently using gloss acrylics (I've seen this with Tamiya and Gunze gloss acrylics). I've not seen it happen with flat paints.

As far as I am aware, there is no way to fix this other than stripping the paint and repainting. Simply overpainting will fill the cracks, yes, but will also add thickness to the rest of the paint, meaning that the cracks will still be noticeable.

Now to be clear, you're using X-20A acrylic thinner and XF-21 Sky and NOT X-21 Flat Base?

How long between coats? Tamiya paints dry very fast and I have never had any trouble airbrushing a second coat even 10 minutes after the first.

Was the paint put on too heavy? Was this brush painted or airbrushed? 

This sounds rather strange. I've never had this happen with Tamiya flat acrylics, though I've seen it on occasion with gloss.

What did you use for your base/undercoat?

As Mike said above, Tamiya flat acrylics dry very quickly - sometimes within a few seconds when airbrushed thinly, though they do take substantially longer to cure.

The only other thing I can think of at this time is that there may have been some extreme/rapid variation in temperature or humidity which may have caused this effect.

I used tamiya undercoat

and I dont think there was that a big of  a dif in temp

A10wrthg wrote:

I used tamiya undercoat

When you say "Tamiya undercoat", do you mean the spray can primer or just ordinary Tamiya acrylic paint used as an undercoat?

A10wrthg wrote:

about 5 min it was airbrushed it was thinned about 60 40 for thinner

That's a lot of thinner. I usually thin Tamiya 2 parts paint to one part thinner. 

Hmmm, can't figure this out. Everything sounds ok.

I wouldn't put it down to over-thinning - I often use up to 3:1 or 4:1 thinner:paint with Tamiya acrylics and don't have any issues.

Very strange...

Phil_H wrote:

Hmmm, can't figure this out. Everything sounds ok. I wouldn't put it down to over-thinning - I often use up to 3:1 or 4:1 thinner:paint with Tamiya acrylics and don't have any issues. Very strange...

I agree Phil. I wasn't implying the cracking came from too thin of a paint mixture, I was only saying that is too thin for the average paint for coverage and all. 

No problem Mike, everyone has their own methods which work for them.

I'm fast running out of ideas here and we're getting to the "clutching at straws" options:

• Is the paint new/old? (Under normal conditions, Tamiya paint can be stored for a long time - I have some which are in the 20-25 year old range which work fine)
• Has the paint been exposed to extremes of heat or cold?
• Has the paint been thinned for an overly long period (say, more than 2 weeks) before use?
• Has the paint thickened or been partially dried out in the jar and been  reconstituted by adding thinner? When stirring the paint, are there any strings or lumps which are still there after a few minutes of stirring?
• Has the paint been thinned with anything other than Tamiya thinner? eg. water, Windex etc
• Is the cracking localised to a few spots or is it more or less evenly distributed over a large area? If localised, it might suggest dirt/oil on the surface or moisture splattering from your air hose (are you using a moisture trap?).