Hi all,

While taking a closer look at one of our "under restoration" pieces at the RGVRRM, I noticed that there was a couple of very noticeable locations where the paint has begun to separate from the sheet metal it was applied to. Upon closer inspection it appears, that the sheet metal is galvanized steel.

Would any of you have any suggestions, pointers, tips, experiences in-kind worthy of sharing on how to properly bond paint to this surface and keep it from peeling as it has begun to?

The attached picture should illustrate the issue. Thanks all.



By the way, the locomotive is a 6 or so ton Plymouth Model BL powered by a Buda gas motor.

More details can be found here: http://rgvrrm.org/about/railroad/plymouthbl/index.htm

Here are a couple of sources of information:
http://www.sherwin-williams.com/do_it_y ... izedMetal/

http://www.galvanizeit.org/images/uploa ... tsteel.pdf

Basically, you have to get the oils off of the galvanized metal, then roughen up the smooth surface to provide something for the paint to bite into, then apply a galvanized primer before reapplying the top coat.

BTW I saw that little locomotive last week and its an amazing piece, considering the work that had to be done to restore it.

Luther, the correct way to fix your paint problem is to replace that section of galvanized steel with special "passivated" galvanized steel that is paintable. If you look closely the rest of the steel that is applied to the wooden frames on the Plymouth BL exterior is also galvanized steel and the paint is adhering fine. Apparently when I installed that small section I must have used the wrong material.

I believe the trade name you want is "Galvanneal", or something like that. I think you will need to pry out the nails that hold that piece in place, remove the hinge, remove and replace that piece. Then if you sand it lightly, clean it with a solvent and first apply an etching primer you should have better luck.

Sanding, solvent and etching primer is the method I used to paint all of the passivated galvanized steel on the exterior of the Plymouth.

Sanding and cleaning that section will only give you the same results in another 5 years or so. It has to do with the formation of phosphates on the surface of the zinc which inhibits proper bonding of the paint. It is not a surface roughness or cleanliness problem. The phosphates reappear under the paint and break the bond.

By the way the original drawings (ca 1919, yes we have some copies) specified "sheet iron". I could not find any sheet iron in 2005, and since the metal is in contact with wood I felt that galvanized steel would be more resistant to the moisture from the wooden frame. Looks like I applied the wrong material to that small section.

Cheers, Kevin.

My paint company recommended a zinc phosphate primer so that the peeling would not occur. The zinc phosphate is a thin, yellow-greenish color which allowed the final coats to cover properly and yet show a tell-tale color if the final coat was not applied thick enough for good coverage. I never had any peeling in over 25 years.

The article referenced mentions this primer near the end of the article (http://www.galvanizeit.org/images/uploa ... tsteel.pdf).

Harry Nicholls

Hmm, interesting that Sherwin Williams, who has been making paints since 1866 doesn't know what they are talking about.

Nothing against any particular vendors fine products or helpful advice. But as the individual who applied the paint seen in the photo supplied by Luther I can assure you that both sides of the peeling and unpeeling paint (notice the seam between two different pieces of metal) where prepared and painted the same way and in fact on the same day (i.e. same humidity and temperature). The ONLY difference is in the metal. I know since I fabricated those metal pieces and must have used two different materials. I know that I fabricated the metal pieces, applied them to the wooden frame and then painted the finished assembly. We could of course verify this by removing all of the metal and searching for overspray on the wooden frame that would have resulted if I painted the right most portion before installing the piece on the left.

You will also notice that there are metal slats below the peeling paint that were fabricated from the same metal (paintable galvanized steel) as the portion on the left side of the seam above. Notice that the paint is still firmly adhered to those as well (at least as recently as the date of the photo.)

I did in fact do quite a bit of research on what metals to specify in place of the original iron sheets and how to best paint them. And I did consult many paint manufacturer’s datasheets before proceeding. Indeed there are many fine commercial products that address this concern, however my wallet was not thick enough at the time to justify those products. I did find a combination of paintable galvanized steel with affordable self etching primers (from the auto restoration hobby field) that seemed at the time to work. Of course if anybody would like to donate a $10,000 state of the art paint job for the locomotive in question I’m sure it would be appreciated.

Paint, a sticky question for sure.

Cheers, Kevin.

When I was in Uncle Sam's canoe club, and a member in good standing of the Gulf of Tonkin Yacht Club, we used red lead on steel and zinc chromate on all other metals including galvanized steel with no problems. But you must follow standard practices of getting the surface prepped correctly. There no shortcuts in this area of painting.

Later!
Mr. Ed

Unfortunately, Red Lead paint has been on the US "can't have that" list for quite a few years now. Along with toilets that flush properly and coming soon incandescent lightbulbs. You can fly across the pond and get some in Europe, but they would probably throw you in jail trying to come back home with it.

Cheers, Kevin.

I wasn't suggesting they use red lead. I was explaining the two types of primer we used. Zinc chromate is what we used on all other metals including galvanized steel.

Later!
Mr.
Ed

That would be it, then. Getting paint to stick to galvanized is quite a challenge. The zinc is trying to oxidize to save the steel underneath. It wants to oxidize on its surface.

Edit: Since this posting, I've been keeping an eye out for info about painting galvanized. The issue is that you are painting NEW galvanized. There is no way to get paint to adhere to fresh galvanized. However if the galvanized had "6 months" (outdoors in real weather) it materially changes - that is the surface oxidizes. This weathered surface can be convinced to take paint with the right primers and prep (read: prep that removes contaminants but does NOT strip off this oxidation layer). Paint manufacturers have instructions on that.

Whenever the membrane gets pierced, you have a 3-way intersection of bare metal, paint and air (and sometimes water). Something special happens at that intersection. Often it causes the paint to separate and lift, meaning the blister just keeps getting bigger. It could be the other panels' paint membranes are intact. Or the steel is different. Or maybe some oil got on there that escaped the initial prep.

You could burn off the zinc plating with sandpaper or a roloc, get down to bare steel.


The $10,000 job would just fall off too. Surface issues are surface issues.

On WM 75, I found serious problems with the underlying paint, after I had bought the $200 Awlgrip. I knew it would just fall off in 5 years anyway... so I switched to $30 Rustoleum and saved the Awlgrip for a worthy project.

I've also done painstaking prep on a speeder, painted Rustoleum and watched the colors fade badly INSIDE A YEAR. Now I have to do it again. That is why, if there's a certain key product that will make all the difference, I'll find the money.

Speaking of key products, that "$10,000 paint job" is probably a 2-pack urethane. You, as a mere mortal, cannot spray that stuff. But you can brush/roll it. And since most of the cost was for the expert in the bunny-suit and all the overspray he wastes, you can get that $10,000 paint job for well under a grand. This is why I like Awlgrip.

For a locomotive small enough to permanently reside indoors, why was the decision made to use galvanized metal?

The locomotive is indoors, but in an unheated building (for now, maybe not forever) in upstate NY. So there is quite a bit of condensation (dew) collecting on the equipment during the spring and fall of the year. The exterior metal "skin" is wrapped around a wooden frame (as per the original design drawings). So the concern was that moisture collected by the wooden frame would cause untreated steel to "rot" from the inside. Also the skin overlaps itself in spots (i.e. the seam seen in the photo).

So we could have painted the inside of the metal skin and sealed the wood, or hopefully use the galvanized steel and avoid this problem. In retro respect perhaps we could have created "one sided" galvanized steel by sanding off the zinc from the outside. But that would have involved figuring out exactly what surfaces would end up as exterior surfaces since in some places (the seams) both surfaces are "interior" surfaces.

So we decided to bite the bullet and suffer with having to paint the galvanized exterior. The galvanized steel vendors "claim" that their brand is easier to paint. The paint vendors "claim" that their paint system sticks to anything. Whom to believe ? I know that things were carefully prepped, lightly sanded, wiped with solvent, tack clothed, painted on mostly dry cool days, indoors, etc.

Compared to all the other repairs necessary (lots of replacement parts fabricated including sleeving a cracked cylinder bore, a radiator core, gears, bushings, etc.) the fact that a small section of the paint is failing seems to me an easily surmountable problem.

Strangely enough the original design drawings specified "sheet iron" which will of course form its own protective "oxide" skin on the internal surfaces and these problems mostly go away. When we received the loco none of the original “hood” existed (frame, skin, etc.) so we had to fabricate it all from scratch and make substitutions of modern materials for those we could not obtain. Perhaps those old dead guys (no offense to women) that designed this loco were on to something when they specified "sheet iron" back in circa 1919. I could not find a source of "sheet iron" in 2005.

Cheers, Kevin.