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Home , Forum , Coatings & raw material failures , PU paint bubbling

Tuesday, 30 September 2014

PU paint bubbling

3 Posts

Tuesday 19 December 2000 1:00:00 am

I repainted a used car. The seams around the wheel-wells (which
are spot-welded) commonly give rust,
> so I applied an inorganic zinc-rich coating, and used an epoxy primer on
top of this. I drove the car then
> for about four years, without finishing the paint job, and no sign of
rusting at the seams was evident at all.
> It looked AOK. Then I went ahead and primed and painted the car with a
catalyzed polyurethane automotive paint.
> It looked great for 6 months, but now there is bubbling of the PU paint,
at those seams. Its hard to imagine rusting
> having started at exactly the time I did the final finish. So why does
the PU paint now bubble, and is there a way
> to avoid this next time? K J Strack
>
>

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Thursday 21 December 2000 1:00:00 am

Bubling of Poly is generally due to the formation of CO2 within the film. When the CO2 leaves the film bubbles and pinholes are formed on the film. Our experience of CO2 formation in a Poly could be due to
* Moisture or Dew on the surface on which Poly is applied
* Moisture in the spray system
* High humidity above 85 to 90% at the time of application of the Poly
* Accelerated dry and Poly reaction due to high humidity or use of catalyst
* Solvents used in the Poly or its diluent are not free of water. Special grades of solvents are used for Poly
* The solvent or the diluent used for Poly is exclusively or has high content of Xylene
I am sure there could be other reasons and stay interested in hearing of other's experiences.
Best wishes,

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Sunday 14 January 2001 1:00:00 am

I completely agree with Mr. Sen's reply. But I have a query.
If the bubbling is b'cos if co2 emission (due moisture contamination), then it should have appeared immediately. But in this case, everything seemed ok, till 6 months. Is this true?. Mr. Sen.
And Mr. Strack, when you re-primed your car, what is the primer you used?.
regards,
krishna

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Friday 19 January 2001 1:00:00 am

Mr. Krishna
Thanks for your interchange. I would not imagine a PU automotive topcoat or any aliphatic PU topcoat to have permeability problems. But I will also not totally overlook such a possibility. Could this have taken place allowing moisture to slowly seep in through the topcoat and cause bubbling after a period of time? Possible, would you say?
Thanks.
A. SEN.

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