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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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CARC paint is blistering from aluminum parts
2007
Q. Using one-part CARC paint (tan), spraying wash primer, and epoxy primer drying after primer. paint employee - Anniston, Alabama |
ACRONYMS: |
A. John,
Is this process being carried out on bare aluminum? If it is it would suggest a pre-cleaning problem before the application of the etch primer. Check that the surface is fully degreased and cleaned and that once cleaned the parts are not handled with bare hands as this will re-contaminate the surface.
Aerospace - Yeovil, Somerset, UK
2007
Q. Yes, bare aluminum. It is being washed before but not sure how or with what, We are water break testing it also.
The parts are being handled after washing but it bubbles nowhere near where was touched.
- Anniston, Alabama
2007
A. John,
As it is blistering right down to the base metal and not between layers of paint it would indicate either a surface contamination problem or a wash primer problem.
Ensure that the parts are kept clean before painting, possibly even use a final solvent clean before painting. Once cleaned ensure all operators wear gloves when handling the parts (just in case, you'd be amazed how easy it is to get fingerprints in areas you wouldn't expect).
The wash primer I take it, is a single part primer and that you haven't thinned it. Check that it is in life, if it isn't this may be causing you a problem.
Aerospace - Yeovil, Somerset, UK
2007
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A. Do a vigorous epoxy stir avoiding air inclusions. - Minneapolis, Minnesota, USA 2007 2007 A. Dear John, Here is another point of view approaching your problem from a different direction altogether. First, we have to establish what your painting system consists of: Birmingham, United Kingdom |
It seems that we may have found the problem, Either to thick of a primer coat or not enough dry time.
We have been drying for 45 mins @ 135 °F
I took a closer look and it bubbled kinda around brackets were overspray would build up thicker than the rest.
- Anniston, Alabama USA
A. We process very complicated aluminum parts with extensive masking with the CARC system daily. Adhesion on aluminum is always a little tricky. The water break test mentioned does not tell the whole story. It will test for surface contamination only. Aluminum oxide on the surface will pass a water break test because it reacts the same as the base metal. In our experience, the parts should be deoxidized and or chemical Iridite prior to prime. Surface oxides will cause blistering and delamination from the base material. Cure time of the primer varies with thickness as you have noted. If you talk to the paint suppliers, they will tell you that a full cure of the primer is not required before topcoat. I do not recommend this procedure. Also, the type of thinner used in the primer should be varied with ambient temperature and relative humidity. See product data sheet for recommendations. Precise measurement of thinner additions is critical to proper adhesion of this product. Utilize a #2 Zahn cup to verify each batch.
Bruce Wheeler- New Haven, Connecticut USA
September 17, 2010
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