I have a metal roof that is totally rusted but seems to be structurally
sound--no leaks. However, I am worried about the future. Can I sand
and then coat this metal roof and expect the fix to last a few years,
or do I need to replace the whole thing?
Eventually, no doubt. I took an old machine shed and sprayed one of the
rust converters primers and then painted. That was old (70-80 yr
maybe?) heavy corrugated galvanized, not recent 26 ga, stuff however, so
it is still much heavier than typical new "tin". It's been about 5
years now and is holding up well and the light color makes for
noticeably cooler interior during hot summer.
Whether for house/light current roofs it would be cost-effective I don't
know--it wasn't a whole lot less than new tin, but new tin would have
required adding extra support in this case and that was the deciding
factor for me.
I initially intended to simply pull the sheets and turn them over since
the inside face is good as new, but after starting in it became apparent
that it would have taken essentially the whole winter... :(
On 22 Apr 2005 07:32:32 -0700, firstname.lastname@example.org wrote:
When I bought my farm there were several sheds that had galvanized
corrigated tin roofs. All had at least some rust, and one was almost
entirely rust. Yet, all were solid and had no holes. I just bought a
5 gallon bucket of silver "aluminum paint", and coated the whole roof
using a roller and paint brush. I did no surface preparation, other
than removing dead leaves and junk, and hosing it off the day before
to remove any dirt. I also pounded down all loose nails and added a
few (neoprene washer nails), where needed. One coat of paint and 5
years later it is still mostly fine. However, last summer I bought a
few cans of cheap silver spray paint for a buck a can at Walmart and
touched up the few spots that were showing a little rust again. Maybe
in a year or two I will paint the whole thing again just for
protection. The total cost was about $80 for paint, rollers, nails,
clear silicone caulk (used after painting to seal around loose nail
heads). Sure beats the cost and labor of a new roof.
My animals and hay stay nice and dry...
Once something gets a protective coat of rust, it takes a LONG time for the
remaining material to oxidize (decades, most likely). For example, you will
never see a barbed-wire fence (rusty though it may be), "rusted through."
For example, Aluminum oxidizes very quickly. Looking at a soda can or a bit
of foil, what you see is Aluminum oxide.
In your case, what you want is to keep the protective Iron Oxide coating in
place so as not to expose any of the original material to the elements. I
would think a paint job would be sufficient - the paint not to protect so
much as to immobilize. And look pretty.
Generally true about the red oxide. In fact, road
guards are often just coated with the red oxide in
parts of the country and usually get smashed up
before they ever get eaten up with rust.
However, the op is talking about roofing which is
very thin. I've seen plenty of metal roofing and
siding of corrugated steel that is pitted with
lots of holes).
Again you are correct about leaving the rust there
and just painting. Apply a rust primer and then
an aluminum, or better a zinc, rich paint. There
are specific paints made for this purpose that
will last a long time. Not cheap though.
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