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valejo aluminium problem


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i applied valejo aluminium on gunze white 1000 primer 6 months ago and it looked very nice .six months on i noticed the shine has gone ,the finish has gone flat and there are small hairs appearing like a carpet.what is causing this?

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How long between application of the primer and application of the aluminum? Was the primer a thick coat?

What solvent systems were used for thinning each paint for application?

It sounds like solvent migration from the primer through the aluminum, carrying one or more components of the primer with it to be deposited on the outside surface as your "small hairs."

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the gunze primer was diluted with their diluent "110" dark blue label.rested for 24 hrs then applied the valejo using their dedicated diluent.Nothing else was applied after that.i would not say my application of the primer was a thick coat.

Edited by amin
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The primer was diluted with gunze dark blue label which must be solvent based “light blue for aqueous”,I have used revel dark blue label as well and it dilutes fine for airbrush use.The valejo paint is diluted with their own I am sure alcohol based since nothing else works except their own or alcohol 96% for airbrush use.It is interesting to note that only this model I have was airbrushed with a valejo paint and the only one to to now have this deterioration on the surface of the 2 wings upper side only.All my other models were sprayed with gunze aqueous diluted with their own diluent”light blue label” which must be alcohol and water based or model master enamel diluted with turpentine after being primed or not and don’t show this problem.I also have a primed aircraft airbrushed with gunze solvent based super silver diluted in turpentine and doesn’t show this defect,,all built many months ago.all my models when primed "not all are primed" were done so using only gunze super white 1000.I also have an aircraft airbrushed with valejo but not primed from May last year and it looks perfect.

Edited by amin
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Sounds to me like a solvent migration problem, though a picture would be useful. I'm afraid I can only speculate as to why the top of the wings are more affected than elsewhere. There are too many factors involved and not enough information.

This can happen under the following conditions, and metallics are particularly susceptible because of the nature of their pigments:

  1. Primer was thicker than usual, or for some other reason did not finish out-gassing before the finish coat was applied. This can happen when using a slower evaporating solvent as a diluent.
  2. A finish coat solvent migrates into a porous primer coat and reactivates or partially dissolves a component of the primer, which then slowly migrates through the finish coat, ruining it. This is possible even when using an aqueous/alcohol coating over an enamel type if there is any component of the primer susceptible to water or alcohol. Careful application of the primer to avoid a porous surface, or polishing the primed surface with a fine grit will prevent a porous primer surface.
  3. Application of the finish coat in such a way as to trap its own solvent in higher than usual amounts. Aqueous/alcohol solvent system metallics are particularly vulnerable to this because of the slower evaporation rate of their solvents.

I'm afraid the cure is to sand off the finish coat and reapply. :bandhead2:/>

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I fully agree with your analysis.As a matter of fact i do notice the porous hairs settling on the primed surface every time I prime but do nothing about it and they look the same sticking out of the paint surface in this case.Its interesting to note that I had this problem only with a metal pigment formulation.Valejo is again another case,their formulations are extremely slow to dry and if not primed will chip very easilyâ€.I should have given the model a second coat of paint.I did not have this problem with gunze super silver "solvent based" on another model. The next bare metal model will be airbrushed with alclad not even radio active material can get out.,and it looks even better with time.I will try to take a pic today with my I am a spammer, please report this post. L20 but im not sure its good enough to show the defect.Then I will try posting,,I’ve never done that before hope its not complicated.

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