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Ask the Expert Question-and-Answer Archive by Ron Joseph July, 2005 Paint Detachment from Wood Composite Q. We have a problem with paint detachment on our composite bonded bars that we fit internally and externally to our timber windows. We have only experienced this within the last 6-9 months. We do not put any kind of basecoat on the composite material beforehand as advised by both bar and paint manufacturer. We have changed nothing in the way we spray and the reasoning coming back from the paint supplier is the paint must be curing cold. This is impossible as all windows and there components are dried through infrared heaters. Paint detachment has also appeared recently between second base coat and top coat on timber. Does this suggest something is wrong with topcoat? A. Without actually examining the problem first hand, it is not possible for me to give you a definitive answer regarding the paint failure. Have you checked intercoat adhesion by applying the basecoat and topcoat onto a steel or aluminum surface? You might perform several experiments in which you apply the topcoat over the basecoat under different conditions and then perform accelerated weathering tests to determine if you can duplicate the paint defects. You should also watch you dry film thickness to insure that you don't entrap solvents during curing. If the coatings are waterborne, then insure that you are not painting on humid days and/or cold days as that will affect the performance of the coatings. The substrate might also be the cause of the problem. By conducting tests on different substrates you might be able to identify if the composite material is at fault. If you like, we can help you solve the problem by performing tests in our offices, but since we are in California that might be difficult for you. Alternatively, if you would be willing to consult with me by phone, we might be able to brainstorm the problem and I might be able to lead you to the cause. You could send me digital photos of the process, technical data regarding the basecoat and topcoat, etc. I do charge on an hourly basis, but you can pay by credit card. Good luck and please let me know what you discover. Best wishes, Ron Joseph
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