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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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Historic tin roof refuses to allow primer to stick
October 31, 2010
Hello: I live in Tennessee's oldest town. I have been restoring a turn of the century cottage, which has what I believe to be the original tin shingle/plate roof.
I am in a race against winter to repaint the back end ( south weasterly end) of the roof. It has got me stumped.
Originally, I followed Sherwin Williams advice: scraped off any lose paint, used Ospho rust neutralizer, rolled on Ken Kromic universal, an alkyd metal primer.Then I applied a dtm acrylic.
Within less than a year it started to peal off both the primer and paint.
Sherwin Williams gave me a generous quantity of primer/paint.
But I am confused. There appears to be a greenish blackish substance covering the shingles along with some rust spots, after I scrape the loose paint.I have sanded down to shiny metal to get rid of any rust and this covering. Is this substance my the culprit?
Could the original Ospho or primer have reacted weirdly? What do you think, I am pulling my hair out. I do not want to apply the primer if it is wrong for the task. Brian in Jonesborough.
historic home restorationist - Jonesborough, Tennessee, USA
November 1, 2010
Hi, Brian
I'd like to hear from an historian or a metals conservator on this, because I am wondering if this might be a lead-tin (terne plate) hot dip coating rather than tin or zinc. Most acids/etches will not activate lead, but only make the adhesion worse.
If you google for terne plate, you'll see that there are some experts in the subject, and they may be able both to tell you if you have terne plate, and how to get adhesion on it.
If that doesn't work out, you might need a fluoride based dip to get adhesion, and this is dangerous stuff. If you have a truck-wash in the area, you might see what the operator has to say about the whole subject because they sometimes used hydrofluoric acid based washing solutions on the aluminum and stainless steel tankers. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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