priming & painting a cast iron pipe

Old 04-14-17, 06:06 PM
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priming & painting a cast iron pipe

Hi everyone! I am painting a cast iron pipe just to try to make it look decent in my basement. I first cleaned it using a steel brush and mineral spirits to get rid of as much rust as I could. And then I primed it using Rustoleum clean metal white primer. I went with the clean metal variety b/c it says light rust is ok, which is what I had.

But now it's been about a week since I primed it (2 coats, both within 2 hours of each other) and I'm already having issues. The top part of the pipe (which was the rustier part) is showing darker than he bottom part (which had less rust) and I have a couple of specific spots where rust is clearly showing through. So what do I do? Just more coats of primer? should I try the Rustoleum primer that's made for heavy rust? Are there other brands of primer to try? Or other techniques entirely?


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Old 04-15-17, 04:37 AM
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I doubt applying Rustoleum's rusty metal primer would help at this point. A pigmented shellac like Zinnser's BIN should take care of the discoloration. Assuming you did a decent job of cleaning up the rust I wonder if there might be a minute leak at those locations ??
Old 04-15-17, 05:42 AM
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I think you should have used the rusty metal (red color) primer since it sounds like you did not get the pipe cleaned down to clean, shiny metal. One thing I consider when choosing between the two primers is not the amount of rust but instead go by the depth that the rust penetrates into the metal. Cast iron does not have a smooth surface so very difficult to get it properly clean and you can have to deep pockets and crevices of rust.

For your pipes I would try doing some work just on the rust areas. I would use sandpaper or a file on the rusty spots and take those spots until they are smooth and shiny. Thoroughly clean the spot with mineral spirits or paint thinner using a clean rag for each wipe. You are trying to remove all the tiny/microscopic flakes of metal you've removed so they can't rust later. Then prime one or two coats with your clean metal primer and paint with your top coat.

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