Letter 33010

Need a spec for the coating system for galvanized roofs [Washington] 

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Is there an economical cover coat for a galvanized roof that prevents the trace zinc runoff to stormwater? Any ideas on longevity?

Thanks,

Dave Ashcom
enviornmental engineering - Newcastle, WA, USA

Hot-mopped roofing tar?

Tom Gallant
- Long Beach, CA, USA

A lot of work has been done in Euope over the past few years about Zn runoff from rain on galv materials. There's no good evidence yet that it is any problem, so one could ask why you'd want to prevent it.

Assuming there is some technical reason, you can buy precoated galvanized sheeting where an organic coating is factory applied. The Zn is only exposed if mechanical damage to the organic coating occurs.

Geoff Crowley
- Scotland

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