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How to make galvanized roofing look old?

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Does anyone have experience applying acid or other substance on galvanized material? My goal is to make corrugated, galvanized roofing dull and have spots of rust.
I have heard of people doing this with acid and I am aware of the need to collect the runoff and dispose of properly.

Thanks GT

(post #177518, reply #1 of 9)

A previous thread mentioned horse urine as a means of making copper roofing look old. It would seem that it should work on galvanized. But, as they said, getting the horse up on the roof may not be too easy...

(post #177518, reply #2 of 9)

The galvanizing is zinc, which reacts with almost any acid. One could use muriatic, sulphuric (drain cleaner, mildewcide), phosphoric (LimeAway, Naval Jelly, Coca-Cola), acetic (vinegar), citric (lime juice), or whatever. The question is why. The point of the galvanizing is to keep the steel from rusting, developing holes, and leaking. The zinc will age on its own fast enough with acidic rainwater.

All the acids I mentioned are non-toxic when dilute. Strong acids and alkalis can be disposed of in the kitchen sink with plenty of water.

(post #177518, reply #3 of 9)

vinegar will dull the surface for applying paint. but why would you want to rust perfectly good tin...while your at it shoot a 44 magnum through the roof a few times and fill the holes up with roofing tar...this will give it a classic look of old tin.

(post #177518, reply #4 of 9)

Look for a farmer with an old rusty barn, maybe he'll swap roofs with you. Just kidding. Seriously I wonder if you could get that look with rust colored paint applied randomly? That way you wouldnt lose any of the protection from the galvanizing. Chuck

(post #177518, reply #5 of 9)

Spray with WD-40 and let the dust collect on it? :-)


(post #177518, reply #6 of 9)

Chuch has the best suggestion, and I have a barn with a rusty roof ,willing to trade for a shiny new one with out bullet holes and tar. Sand blast the spots that you want rusted to remove the zink . People urine will work, invite your buddies over and have a keg party on the roof.

(post #177518, reply #7 of 9)

If you really insist on distressing your galvanized roof, GT, here's how I would go about it. The layer of zinc is very thin and can be broken mechanically. I would first find a way to do this by hitting it with a tow chain, rubbing gravel up and down the valleys, shooting at it with a BB gun or sling shot, or anything else I could think of. Then I would dilute some muriatic acid with water - about one part plus four parts - adding the acid to the water not vv. - and fill a plastic garden sprayer with the mixture. I would then spray it on the roof while wearing eye and breath protection, wait about 10 minutes, and wash off the roof with the garden hose. Any exposed steel would start showing rust almost immediately.

It may be that you're in a dry climate so that you don't have to worry so much about the roof rusting all the way through. If you want to preserve the protection of the galvanizing, Chuck has the best suggestion. Use several shades of flat gray paint, rust red primer, and some black.

As an aside, I wonder how corrugated sheets of CorTen steel would work as roofing. CorTen is the steel used for bridges and other structures since it rusts enough to turn red and then stops. Apparently, the rust forms a protective layer much as aluminum oxide does on aluminum metal.

(post #177518, reply #8 of 9)

There was a thread on this site in late August regarding CorTen - apparently the reality is that it continues to rust and discolors everything below from the runoff. One quote was "Although, Corten steel is still used in some applications, it is no longer manufactured as roofing,
because of repeated problems with improper installation." You can find the full thread by doing a search on "CorTen".

(post #177518, reply #9 of 9)

If you go with the WD40 and the keg party on the roof , dont forget the camcorder. You might win enough money from Americas Funniest Videos to pay for the new roof.