Re: Paint Failure on Outside Metal Roofs


Gatwood, Elden J SAD
 

Denny and all;



Faced with a large number of projects for which I had few answers, I have
been staring at in-service photos for months now trying to get up the courage
to finish some of these horrible weathering jobs off. I've done a few. A
number of them are really daunting.



Roofs are a big part of it. I have a lot of PRR cars to finish, and I think
I have some of their way of dealing with this issue partly figured out.



When the PRR was using plain-steel sheet for their lap-seamed roofs, they
seemed to have less paint flaking problems than when they went to galvanized
roofing (immediate post-war). This is not to say they did not have problem
with those roofs, they just laid on coats of asphaltum, if it leaked, but
otherwise, out of the shop, it was painted. The paint seems to have
gradually failed by erosion of its thickness and rust forming around seams
and rivet heads, again both of which could be temporarily cured by another
coat of asphaltum.



When they went to outside vendor galvanized roofing, with their big rebuild
campaigns, they created a whole different paint problem. The paint flaked
off the roofing, sometimes pretty quickly. The seam caps stayed painted
longer and gradually rusted up like the earlier sheeting. This created that
neat grey/silver sheeting and red/rust seam capping you see on so many cars,
not just PRR (I have photos of WAB, NKP, ATSF, NYC and others in front of
me). There are many subtleties in all this, when you look at a lot of
photos. The rivet heads along the side/roof juncture went to rust very
quickly, and are very visible on many of my photos as small brown dots.



This is also added to by the variations you seen in paint failure seen in
color shifting and rust bleed through. Earlier paints on the PRR seem to
have shifted toward orange and/or pinker versions of Freight Car Color, as
opposed to later versions, which shifted toward a bluish tan-brown or some
mess I haven't completely figured out.



Lastly, are these jobs where the paint has almost worn off. One X26 has me
in awe. The paint has almost completely worn off wood and steel
framing/ends/doors. It is a fascinating patina of gunmetal blue with rust
blotches on the steel, and a suite of pinks, tans, browns and hints of
original red, on the wood. The lettering is almost gone. I do not currently
have the courage to finish that job!



It takes an artist to see how some of this should be created. I wish I had
taken more art classes!



Elden Gatwood



________________________________

From: STMFC@... [mailto:STMFC@...] On Behalf Of Denny
Anspach
Sent: Saturday, October 11, 2008 12:50 PM
To: STMFC@...
Subject: [STMFC] Re: Paint Failure on Outside Metal Roofs



Getting ordinary paint to stick on galvanized metal is a common
problem that has never completely solved, as far as I know. The most
common means of minimizing paint failure has been to apply on the
clean galvanized surface a preliminary first coat of a weak acid, most
commonly ordinary household vinegar. Whether or not the car builders
routinely did that, i.e. cleaned the surface AND applied vinegar, I
know not (but probably someone does).

Denny

Denny S. Anspach MD
Sacramento

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