Graham applies the chromate

Having been blast cleaned by Graham the week previously, it was time for the zinc-chromate primer. For those of us “out on our bikes” during O level chemistry, zinc is an extremely effective corrosion inhibitor-hence its popularity in marine and similarly challenging environments.

Loading the gun with chromate, he chases around the teenage dream in a mist of gunmetal, bringing the tubes to life. Because the frame is earthed and the particles attracted to it, there’s no wastage and it took a mere ten minutes to achieve even coverage. From here it’s a trip to the oven for five minutes at 150 degrees.

Polyester powder coat is phenomenally strong, capable of resisting a hammer blow without cracking when applied by a skilled sprayer but even the best paints can chip. The chromate not only protects the metal beneath-a real boon on mountain, cross and winter bikes seeing hard service; but is pivotal to hiding small blemishes and pitting that can occur during blasting. Many job-lot industrial finishers skip to the topcoat, meaning their pricing looks very attractive on paper but cutting corners here tells in the final finish. Epoxy powder may be extremely thick but remains sensitive to imperfection and demands meticulous preparation.

To illustrate this point, Trevor showed me a motorcycle frame that had been entrusted to their care. Pitting was evident in several areas; little effort was made by the original finisher to mask components or to purge grease and other internal contaminant resulting in some very second rate paint. Blast media makes negligible impression on powder coat so tired looking finishes require softening in a tank of chemical stripper first.

Next Week Grand Finale’




2 user comments

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Poorly finished motorcycle frame

Poorly finished motorcycle frame.JPG
Shaun Audane's picture

posted by Shaun Audane [779 posts]
9th May 2009 - 10:14


Oven curing at 150 degrees

Oven curing at 150 degrees.JPG
Shaun Audane's picture

posted by Shaun Audane [779 posts]
9th May 2009 - 10:24