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I finished a few models on Wednesday and after drying over night I sprayed them yesterday with the testors dull coat varnish. This one: http://i.imgur.com/5T7tp0u.jpg

After setting them down to dry for a few minutes I came back to find that the white paint on the models was cracking Ex 1: http://i.imgur.com/9QB8SbT.jpg Ex 2: http://i.imgur.com/MyhnTuX.jpg

I did the Drone as a test because I thought maybe the paint on the tetra was still damp even a day later but it seems it's just a problem with the GW ceramite white across the board.

Has anyone run into this problem before or know how to fix/avoid it? I'm gonna get some micro sand paper and try and level out the cracks with that unless I get a unanimous don't do that from you guys. Any suggestions are welcome I really want to fix this!

I've seen similar things happen before. This is usually what happens if you paint acrylic on top of oils. The moisture gets trapped under the dry layer and makes it crack. I'm not sure why it is happening here... Could you walk us through a bit more of your process?

Did you wash your models with soap before you began painting? (what kind of soap?)
Was the model primed or base coated?
How long did you wait before applying the varnish?

I'd be happy to post more info if it helps avoid this in the future.

So I didn't wash the models initially just cut them out and glued them.

I primed them with the GW Chaos Black spray Primer

I don't wear gloves when painting so it could be oil from my fingers getting on the model since I don't use a cork or anything I just handle them

I used the GW line of paints to paint the models, and specifically the ceramite white is the one that's causing problems

And finally I wanted about 24 hours after finishing to spray the tetra and the Drone had been finished for a month or 2 and had been handled in a good couple of games I played.

Would some really fine sand paper be a safe way to level out some of these cracks? And should I wear gloves while painting going forward or use a cork to hold the models?

Thanks and hope this helps get to the bottom of this.

Dullcote is a lacquer, lacquers are strong solvents that can attack other paints. That might have been what happened, possibly if you apply lighter coats and allow the solvents to evaporate off before adding more coats, you MAY avoid cracking in future.

It can also happen if the paint underneath is soft. I ruined several models that I'd spent days working on because the primer I used was a type that never really cures properly. When I applied Humbrol Clear (and acrylic clear that I think has an ammonia based additive) it caused cracking. I didn't realise it was the primer's fault at first so I stripped the models and repainted them and once again after applying the clear the paint cracked. I then threw the models in the bottom of my scrap parts box because I was sick of them


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BioLoco wrote:
Would some really fine sand paper be a safe way to level out some of these cracks?

Depends how deep the cracks are. When the aforementioned primer cracked on me, it was right down to the plastic. I kept sanding until the cracks went away and by the time they did, I was looking at bare plastic. On the other hand I've had cracking of Tamiya Smoke as well, but that was only the Smoke paint itself cracking, so I sanded that and managed to get rid of the cracking before I had sanded all the way through my base colour. Still had to repaint most the model though.

And should I wear gloves while painting going forward or use a cork to hold the models?

Usually not a bad idea... but I often don't do that and rarely have finger-print related issues.

BioLoco wrote:
the Drone had been finished for a month or 2 and had been handled in a good couple of games I played.

That sounds like plenty of time for something to cure. I think AllSeeingSkink's suggestion that the Dullcote attacked the paint, is probably the most likely. How long have you had the Dullcote? Sometimes if cans are left sitting a long time they can separate, so you end up with a much higher concentration of the solvent. It could be that it soaked though and then started lifting the paint off from underneath. You could try hitting the white with Ard Coat or another varnish before you spray, to protect the surface.

With regards to sandpaper... If the paint is secure and not flaking, then I'd try just painting over it with another coat of white, and see how it looks (make sure the Dullcote is cured first). I assume you don't want to go to all the trouble of stripping the paint off and starting again, so do the easy fixes first. If you still want to try sanding it after that, then you'll still be able to.

AllSeeingSkink wrote:
Dullcote is a lacquer, lacquers are strong solvents that can attack other paints. That might have been what happened, possibly if you apply lighter coats and allow the solvents to evaporate off before adding more coats, you MAY avoid cracking in future.

I think that might have had something to do with it, I'm definatey going to try a lighter coat next time, as I've lacquered that color before and it came out fine. That's partly why I so confused when this happened.

 Smacks wrote:

With regards to sandpaper... If the paint is secure and not flaking, then I'd try just painting over it with another coat of white, and see how it looks (make sure the Dullcote is cured first). I assume you don't want to go to all the trouble of stripping the paint off and starting again, so do the easy fixes first. If you still want to try sanding it after that, then you'll still be able to.

I'm going to give the sandpaper a shot tomorrow. The cracks are very small and surface level so hopefully I can just flatten them out by being real gentle with it and then touch the model back up. It would be a real shame if I had to re-do the whole thing.

Thanks for the responses guys you've been a big help. I'll let you know how it goes down tomorrow!