John

No practical experience with this, but gut instinct suggests that an
external acrylic paint system is going to perform better due to the
likelihood it will accommodate the thermal movement of the copper better
than an enamel-based system.

I'd be talking to the paint manufacturers' about primers because I
suspect that they will have strong preferences about surface preparation
and priming on metal surfaces.  I'm not a fan of paint manufacturers'
propensity to rabbit on about warranties etc - we know more than they do
about the likely long term performance and the issues / consequences -
but they will provide a good starting point for understanding the
optimum parameters influencing adhesion of their paint system onto a
given substrate.

If the copper will never be painted again, then mechanical abrasion is
always going to provide a better 'key' for the paint ... but it will
mean that future exposure of the copper will not be possible.

Here in Sydney we are seeing a trend towards painting copper downpipes
as a means of protecting against theft - the NSW State Government's
Heritage Branch is located in a 19thC sandstone building where the
original cast iron downpipes were replaced with copper ... and replaced
and replaced and replaced and replaced ... the latest plan, reviewed by
a panel of technical specialists, is to paint the copper downpipes in an
attempt to make them look worthless!

Good luck.

David West
Executive Director
internationalconservationservices
T:     +61 (2) 9417 3311
M:    +61 (411) 692 696
E:     [log in to unmask]
W:    www.icssydney.com
sustaining your heritage
 
-----Original Message-----
From: The listserv where the buildings do the talking
[mailto:[log in to unmask]] On Behalf Of John Leeke
Sent: Tuesday, 27 October 2009 8:53 AM
To: [log in to unmask]
Subject: [BP] Painting Copper

How do you prep and paint exterior copper?

Our issues are removing mill oil, whether or not to scruff up the 
surface, and what paints to use on new custom-fabricated copper gutters.

We're thinking of acetone and rags to remove the mill oil.

The Revere copper book recommends scuffing up the surface with sandpaper

or an abrasive pad. and then quotes extensively from Benjamin Moore on 
products.


Take care, work safe and keep in touch.

John
by hammer and hand great works do stand
by pen and thought best words are wrought

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