Hello everyone. I wish that I had found this forum before embarking on this project, but better late than never. At any rate, I'm looking for opinions as to whether I screwed up or not during a recent repainting of my metal house roof.
The story begins when I replaced my dilapidated asphalt shingle garage roof with new pre-painted ( blue ) 'full length' corrugated metal. This came out excellent, but it made the ~50 year old sectional ( green ) corrugated metal roof on my main house look even worse in comparison. I priced out a similar replacement with new pre-painted 'full length' corrugated metal on the main house roof, but the 1600 sq ft required priced this option off the table.
The existing sectional metal main house roof had occasionally leaked, but this was always due to the gasketed roofing nails securing the metal sheeting working loose. Other than surface rust here and there, the metal sheeting itself was in fairly good shape. So repainting at perhaps 20% of replacement cost seemed like a viable option.
I began by pounding down all of the existing gasketed roofing nails, plus installing new self-tapping roof screws in between the existing nails. I then did a wash with brush scrub using a mildew / stain remover ( specifically Behr #62). After rinsing, I then did a diluted acid etch in order to remove as much surface oxide as I could ( specifically Behr #991). The acid etch showed up all of the old roofing nail gaskets which had degraded over time ... which I then simply wire brushed away and hammered down flat.
After another rinse and dry, I then applied a reasonably thick layer of exterior primer ( specifically Behr #436) over the top of everything, including the heads of the new screws and existing roofing nails. I followed this up with two coats of 100% acrylic latex roof paint ( specifically Behr #66 deep base tinted to match my new blue pre-painted garage roof )
My concern here is that the original ~50 year old sectional steel roof appears to have relied on the gasketed roofing nail approach to handle expansion and contraction of the individual metal sheets. By securing all of these metal sheets much more 'tightly' to the underlying roof boards via the extra screws ( which I had to do to stop additional potential leaks from the ~50 year old nail gaskets continuing to fail), I am now basically relying on the elasticity of the new roof primer and paint to absorb expansion and contraction. In other words, with gasketed nails only, the separate steel sheets were able to 'move' a little bit in relation to each other as they expanded and contracted. But now that they are screwed down tightly, it's probable that thermal expansion will result in the steel sheets having to 'hump up' a bit between the vertical rows of screws / nails.
Your thoughts and recommendations would be greatly appreciated.