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repainting metal roof

Posted by johnmari (My Page) on
Sun, Apr 27, 08 at 16:49

(I apologize if this has already been covered exhaustively, I did run a few searches to no avail.)

The bay window on our ca. 1900 house is roofed with metal, I'm guessing it is some flavor of steel but I'm really not sure. There is some very light surface rust on the charcoal-grayish surface but no sign of loose material or rust-through and no leaking, thank goodness. We'd like to stave off any further deterioration for a few more years with minimal expenditure of cash and/or effort - there's just too much else to do right now! Is there any particular primer and paint we should use or is your basic Rustoleum type rusty-metal primer and paint fine?

Follow-Up Postings:

RE: repainting metal roof

Hello Mari. There is quite a bit of info in the link. Sounds like you want to check with a good paint store for metal roof primer/paint. Hope this helps.

Here is a link that might be useful: Old House forum

RE: repainting metal roof

Thanks - the paint store people I've talked to thus far have been a tad on the clueless side (seems like they're all hiring numb-brained teenagers) but I'll keep trying. Thankfully our roof looks nowhere near as bad as the guy's in that link, and it's low enough to be easily reached with a stepladder instead of having to dangle from safety harnesses. :-)

RE: repainting metal roof

usually that metal was copper. if it is you can spend half your life cleaning it. Heavy Metal Polish is awesome. @$20 per pint at a Trucker's Repair Shop. think peterbuilt or frieghtliner.

any. maybe try POR 15 directly on it. it works directly on rust so....

RE: repainting metal roof

Nope, it's not copper. (I WISH! But this house was far too modest for that even the day it was built... just a factory worker's cottage in an old mill town.) I chucked a magnet out the upstairs window over the bay window and it stuck to the roof so it's definitely some flavor of steel. :-)

I was paging through the most recent issue of Old House Interiors and noticed that AFM Safecoat is now making a low-toxicity roof paint called Roofguard so I'm looking into that - most paints made for exterior metals are viciously toxic, I've learned. Heavy metals and all kinds of good (ha) stuff like that. I'll see if it's compatible with this POR 15 stuff, which has to be topcoated with something but their Flexcote topcoat colors kind of suck.

RE: repainting metal roof

No, by far the most common "steel" roofing material for home use in years past is terne-coated steel.

Copper was used only on high-end homes, and normally only for accent areas (such as the "roofs" on oriel windows) or valleys on slate roofs.

Terne is an alloy of about 80% lead and 20% tin. The iron/steel sheeting was hot dipped into the mixture.

Advantages of it were that it was durable and a LOT cheaper than zinc galvanizing.

Over the years the terne coating will wear off, especially if the roof is not kept adequately painted. That's why you're seeing surface rusting.

Repainting the roofs is not hard, but it is rather exacting.

You need to wash the roof thoroughly. I used a bucket, a hose, and a very stiff scrub brush on a pole. Using an abrasive nylon or even brass scrubber pad will not only remove adhered dirt, it will remove some loose paint, surface rust, and will rough up the surface so that the new coat of paint adheres well.

For soap I used liquid dish detergent. You want something that will clean well but which won't leave a residue. A lot of people use Spic N Span or something with a lot of TSP, but I know more than one person who stained the living hell out of the sides of their house that way...

A power washer would be a good way to go these days, but you still want to brush the roof to get any adhering dirt loose and flushed away.

If there is any loose paint, scrape it off, but be gentle. You can punch a hole in a metal roof fairly easily. Paint can remain, but it has to be tightly adhered.

For rusty areas, you can use a brass brush to knock the rust down and then hit it with a rust converting primer.

Then you need to inspect the valleys, flashing, seams, and nails and repair any popped nails or bent seams.

Be very careful what kind of roofing cements you use. Not all are suitable for use on metal roofs and they can actually interfere with the paint layer.

Once everything dries well, you need to consider paint...

I'll say this right up front. Good roof primer and paint is NOT cheap.

Expect to pay in the vicinity of $40 to $80 a gallon, possibly more.

I used Calbar ( to paint the roof on my parent's house some years ago.

That was one nasty job. It was a full three story house with 10-foot ceilings, so the peak was close to 50 feet off the ground, and it was HUGE.

But, I took my time on prep and application, and it was holding up well nearly 10 years later when my parents sold the house.

RE: repainting metal roof

Thanks for the detailed info, kframe19. Happily, it's only a one-story bay-window roof about 6 feet wide and 3 feet deep, a single piece of metal, easily reachable with a stepladder... if it were the whole house roof we'd hire it out, DH just does not have the time to tackle such a huge project! But, the main roof has asphalt 3-tabs, which we're going to save up to replace in a few years assuming they hold out. I have been able to examine the roof pretty well by sticking my head out the bedroom window (it's only about 2' over the bay roof) and it's in surprisingly good shape given its obvious neglect, so it looks like just clean, prime and paint. By "knock the rust down" do you mean get down to bare metal? There's no loose material, either rust or paint.

I checked out the Calbar website but the nearest dealer is quite the hike away, so I'll see if they can mail me a few color samples. Since it's such a small area we wouldn't need much, thankfully, a gallon apiece would be more than plenty.

RE: repainting metal roof

---By "knock the rust down" do you mean get down to bare metal?---

No, just the loose rust and then use a rust converting primer. You have to leave the tight rust on or the primer won't work.

RE: repainting metal roof

Excellent, thank you!

RE: repainting metal roof

Kframe, thanks for the tip on Calbar paint. I never heard of it, but we used SW industrial paint 4-5 years ago & it hasn't held up despite meticulous prep.

RE: repainting metal roof

Yes, hendricus is correct. The scaly stuff goes, but everything else is addressed by the primer.

As for paints, Google is your friend. There are other roof paint makers out there and you'll probably be able to find a dealer for one of them somewhere near you.

That's rather disturbing to hear about the Sherwin Williams pain, Antiquesilver. They have a very good reputation overall.

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