What happend with the paint ?

[PierreR89]

I walked by where i have put some of my models and noticed that one of them did not like right and after looking closer this is what i saw.
This is my Kenworth T600 that i built a few months ago.



After looking a bit closer at my others i noticed that it had started to do the same on my GMC Bison but on this it is behind the stripe decal


After i have looked at al of my others it is just these 2 that have this problem.
I have done nothing different with these 2 before painting them, i sanded them where they needed, washed all the parts with soap and water, rinsed them good and left them to dry for a few days before painting.
After letting the paint dry and harden i put clear on them a week later it was the same type as the paint, they are both acryl type and have never done something like this before.
The rest of the trucks does not have this problem, it is just the back of the sleeper on both.

Does anyone know why this happend and why it is just this shade of red that is affected by it?
The others with darker red and other colors from the same brand looks just fine and not a hint of anything like this about to happen.

There is no other way to fix this then to remove the paint from the whole back of the sleeper and repaint it or there is another way?
The Bison might be harder to fix since it is behind the decal and aslong as it does not get any worse then this i can live with it.

[Oldcarfan27]

Looks to me like mould release was left behind before painting. Also, on the Kenworth, it looks like primer wasn't used underneath the red paint. Primer is needed to give the paint something to hold on to.

[peteski]

I have painted many models using "stinky" plastic safe paints (like old-fashion Testors) without primer.  Every extra layer of paint (or primer) adds thickness to the paint, decreasing the model's realism. The thinner the paint layer is, the more realistic the model looks (and has crisper surface details, not obscured by multiple paint layers). I only use primer if I use paints which will attack (craze) plastic.  Yet, even without primer, I have never had paint peel or separate like that.

Here the paint not only separated from whatever is under the paint, it has cracked (shrunk?).  I don't have a good explanation, and we also see many examples on this forum of paint incompatibilities with primers or with clear coats.

What were all the layers of paint used on that models? What brands?

From the initial post write-up I suspect those were the water-based paints.  Those might need primer over bare plastic.  I have no experience with these in that application - I do not use it for this type of work. I only use water-based paints for weathering or washes.  I still only use "stinky" paints for my models.

[Muncie]

Looks like it might have been a temperature or humidity problem - I had that happen painting in a cold garage.  Usual prep work - I had the model and paint in the house and took them out to the garage for painting.  Best if paint, model, (air supply if air brush) and room temperature are the same temperature and are within the proper working temperature range.

[Claude Thibodeau]

Hi Pierre!

Happened to me once, and I could establish that it was caused by a not fully cured colour coat, sealed too soon with a clear coat (it was Tamya's TS-13 in my case). When this happens, nothing can be done but stripping all paint to bare plastic and start again.

Sorry if this is your issue here...

CT 

[Venom]

On 1/11/2021 at 9:52 PM, peteski said:

I have painted many models using "stinky" plastic safe paints (like old-fashion Testors) without primer.  Every extra layer of paint (or primer) adds thickness to the paint, decreasing the model's realism. The thinner the paint layer is, the more realistic the model looks (and has crisper surface details, not obscured by multiple paint layers). I only use primer if I use paints which will attack (craze) plastic.  Yet, even without primer, I have never had paint peel or separate like that.

Here the paint not only separated from whatever is under the paint, it has cracked (shrunk?).  I don't have a good explanation, and we also see many examples on this forum of paint incompatibilities with primers or with clear coats.

What were all the layers of paint used on that models? What brands?

From the initial post write-up I suspect those were the water-based paints.  Those might need primer over bare plastic.  I have no experience with these in that application - I do not use it for this type of work. I only use water-based paints for weathering or washes.  I still only use "stinky" paints for my models.

I also never use primer and never have adhering type issues. I just wash the parts with soap and water and rinse them well. What Claude mentioned sounds very likely though.

Edited January 13, 2021 by Venom

[PierreR89]

On 1/13/2021 at 1:47 AM, Claude Thibodeau said:

Hi Pierre!

Happened to me once, and I could establish that it was caused by a not fully cured colour coat, sealed too soon with a clear coat (it was Tamya's TS-13 in my case). When this happens, nothing can be done but stripping all paint to bare plastic and start again.

Sorry if this is your issue here...

CT 

That might be what happend.
I suspected that it was the only way to fix it, just have to think of a way to protect the rest of the model from any overspray when i fix it because it is just the back of the sleeper and nowhere else.
Also i dont want to repaint the whole model.

[Claude Thibodeau]

Hi Pierre!

Then, you got your work cut out for you. Good luck with the spot repair.

CT