Hi Everyone-

The Alexander Chapter-NRHS has started the rehab of ET&WNC boxcar #434. Recently, evidence has come to light that the car had a natural "silver colored" tin roof.

Of course, the car today has a rusty tin roof- not much more than surface rust and some minor pitting- and we have treated it with POR-15.

However, next we need to paint it, but we don't want to use some sort of bright gaudy silver or dulled down battleship gray. In essence, we're looking for suggestions to come up with the best paint to simulate weathered tin.

Any suggestions?

Thanks!

Matt Bumgarner

Aluminum paint with some BBQ flat black mixed in to your preferred tint.

dave

The roof is probably not tin, it is probably galvanized steel. At the Westerm Railway Museum (http://www.wrm.org) we use cold galvanizing on the steel roofs. This is a material that is 93% zinc. I takes about a year for the zinc coating to get the right color, but than it looks just like the roof looked originally. McMaster Carr 7725T14 is what I usually buy. One gallon will usually do the roof on a forty foot boxcar.

Could be soldered seam terne. Depends on how "original" the existing roof may be.

dave

Tin roofs do exist. But they're tin and lead, they don't rust. "Tin roof, rusted" is almost certainly not tin, but galvanized steel.

Galvanizing is a zinc coating. It works because zinc is cathodic - in galvanic corrosion, it wants to corrode before steel does. You've heard of "replacing the zincs" on a boat, that exploits the same effect.

If the steel is relatively intact and you can remove it, take it to the local galvanizer. This is a shop that will galvanize anything you bring them. They dip it in sulfuric acid to burn off rust, paint, etc., then they dip it in molten zinc. IME it's good to show up with a fairly large load, since they have a minimum charge per batch. Aside from that you pay by the pound of zinc added.

You could also replace it with brand-new "tin roof, unrusted" obtainable from lumberyards etc. Provided you can get material that matches thickness, width, pitch and depth to your satisfaction. This can also be custom made.

If you really want to paint it, well, remember galvanized material is both ideal and historic. One option is what Dave Johnston described: "Cold galvanizing compound",
http://www.zrcworldwide.com/p_zrc.asp
http://www.clearcoproducts.com/cold_gal ... ounds.html
http://www.mcmaster.com/#cold-galvanizing-paint/=4f8xdt
A gallon can is unnaturally heavy, 3-4 times the weight of paint. I'd worry it would break a paint shaker. Stir it a lot, and stir it quite often as you paint, as the "good stuff" will want to settle to the bottom. To function as a galvanic protection I would think it needs to be painted on bare metal. And you don't need to topcoat it. Easy application! However you do want good prep. Don't try to apply it over old paint, tar, dirt etc.

Here's a rail project they finished with this stuff.
http://www.zrcworldwide.com/a_rail.asp

Cold galvanizing also comes in spray cans. If you use them, you MUST finish the job by inverting the can and spraying until it sprays clear. If you don't, the can will be internally plugged up the next time you go to use it. We lose a lot of cans that way at WRM.

If you just don't want to galvanize, then I'd say paint it in the usual way you paint metal. WRM does what Seashore taught us, Awlgrip 545 primer (comparable to Variprime, but brushable) ... which will accept just about anything as a topcoat.

A tin roof is actually steel with a tin coating. An alloy made of just tin and lead is solder.

I checked out the Awlgrip primer, and then saw that the price per can was $38.13. Not too bad, until I noticed that was for ONE QUART! You guys are painting railcars with that stuff?

Let's start over: Matt, just what metal is your roof really composed of? What condition is it in? How will it be stored?

dave

Except when used to coat steel or sheet iron, in which case it is properly called "terne metal". This is often corrupted in the vernacular to "tin metal". Terne metal very likely predates the use of zinc in the Galvanizing process.

Back to the roof in question, if it is preformed panels with interlocking seam caps, it is likely a pre-manufactured product for car roofing (Murphy, Hutchins, etc) and was most likely Galvanized when new. If the roofs were covered with sheets cut on site with soldered seams, it is most likely trene metal.

Terne metal tended to turn a darker gray when it weathered than Galvanized.

Company records show that the car was refurbished and a new "metal roof" installed in 1947. Photographic records show that the car still has this "new" roof on it.

The condition of the roof is light surface rust with very minor pitting. I do not know if it is tin, steel, galvinized steel, tin-coated steel, or zinc-coated steel. A magnet will attract to it.

The roof does indeed appear to be pre-fab panels with overlapping, interlocking seams.

We have wire brushed it twice, sanded it where needed, air blown it three times, wiped it down with Naptha, and already applied a coat of POR-15.

The car is currently indoors and will be displayed and stored outdoors under a car barn .

Thanks!

Matt

When you wireburshed it down, was it rusty on top or flakes of zinc or lead on top of the rust? Could just be sheet iron.

dave

Dave-

It was just rusty- no flakes of anything. It was very, very light rust at that.

Thanks

Matt

Sounds like sheet iron or steel. Since the primer is on and OK, tint a high quality metal paint to suit and apply after scuffing. Expect the usual painted metal stuff as it ages - UV deterioration and eventual adhesion and consolidation issues.

dave