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aribert 06-18-2013 11:17 AM

repainting steel garage doors
 
Greetings all:

I need to repaint some steel garage doors. I did not find too much applicable in the archives except this link: http://www.diychatroom.com/f4/paint-garage-door-146848/

After 25 years, the finish on the steel garage doors are sporting tiny rust spots http://i1199.photobucket.com/albums/...b3a1724686.jpg These spots have been visible for the past 5+ years and have not been growing measurably. Only the fuzzy spots are rust - the dark lines / spots that follow the grain are bare metal from my effort to clean a local surface with a relatively mild (automotive) grease & wax remover for the picture. I was a bit surprised that I was able to wear the paint away, rubbing with a paper towel and G&W remover - I am wondering about the durability of the substrate for top-coating.

For much smaller metal parts I either sand blast (if very rusty) or use a phosphoric acid wash, followed by a 2-part automotive epoxy primer (PPG DP50 or DP90).

What should I consider for clean & prep, primer and topcoat? The adjoining trim is gloss SW white Superpaint. I would like the topcoat to look the same.

One thing to note is that I have limited water available for cleaning/prep - I am hauling it in in containers and will not have any pressure rinse capability.

Gymschu 06-18-2013 11:39 AM

All you really need to do is gently sand off the rust, spot prime those spots with a "Rusty metal primer" and repaint them with an all-surface enamel (latex or oil). Sherwin-Williams has a nice ASE paint that would be perfect for your garage doors.

Jmayspaint 06-18-2013 12:15 PM

Quote:

Originally Posted by aribert
:

I was a bit surprised that I was able to wear the paint away, rubbing with a paper towel and G&W remover - I am wondering about the durability of the substrate for top-coating.


What should I consider for clean & prep, primer and topcoat? The adjoining trim is gloss SW white Superpaint. I would like the topcoat to look the same.

One thing to note is that I have limited water available for cleaning/prep - I am hauling it in in containers and will not have any pressure rinse capability.



















With the existing finish rubbing off that easily, it could be oxidized to some degree. Even just washing it with a brush and a bucket would help. If you can't really rinse in well, use very deluded cleaner or none at all. Just agitating it with water helps.
When the surface is dry, rub your hand across it. If you pick up any chalky substance at all, it needs to be dealt with. Maybe use an adhesion promoting additive.
Not many garage door finishes I have seen are very prone to oxidizing. But there are some...
If you get a stable surface, and prime the rust, I don't see why you couldn't put super paint on the door too.

user1007 06-18-2013 03:42 PM

I would think about a rust inhibiting, self-etching metal primer on exposed metal after you remove the oxidation. If you cannot, use a rust converting product.

SPS-1 06-18-2013 07:00 PM

The steel door is probably galvanized (zinc plated). Galvanized steel is very hard to get good adhesion onto, and specific galvanized metal primers are used. But it does not sound like you have an adhesion problem -- if you did paint would be peeling off. Rusty dots sound more like improper plating, or damage by something such as wind blowing dust/dirt at your door. Where you see rust -- that is bare steel, so a rust primer is probably more appropriate. But don't go crazy on the door with a belt sander -- you will just take off the protection.

aribert 06-23-2013 01:37 PM

Thanks for the replies. With the rust spots as small as they are - see penny in picture for reference, I think I would be doing more harm than good if I did any mechanical rust removal. Also I think I need to prime the entire surface of the door - if I tried to do spot application I think I would miss too many of these tiny spots.

Follow up question: What primer would you use? On the SW website the description for the latex and oil base All Surface Primer is identical with respect to "Controls rust and corrosion". I already have the latex version - half gallon left over from an aluminum siding repaint project. I have never used a latex primer on steel. Anyone out there to give testimonial that a latex primer will work? I would hate to have the primer cover up the corrosion and have rust grow underneath!

Jmayspaint 06-23-2013 07:28 PM

Latex primers generally aren't great for dealing with existing rust. They can be rust preventative, but if the rust is already there, is a different story. Treating the rust first with Ospho is usually recommended if using a latex primer. At least That's what SW has recommended to me on similar things.
The best rust primer I've used is Rustolem rusty metal primer. Its oil, but will accept latex top coats well if the drying time directions are followed.
The all surface primer will work, just need to deal wit the rust first.

Gymschu 06-23-2013 08:04 PM

Jmays is right.......oil-based rusty metal primer guarantees that the rust gets sealed up and won't come back anytime soon. You can usually buy it in red oxide or gray, and, perhaps even white. The red oxide primer actually bonds to the rust because it basically IS made up of the same stuff as the rust and gives you a sound surface for your topcoats.


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