Best paint for a galvanised/slightly rusted metal roof?

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I used Johnson floor paint from b+m at £25 for 5l was pretty good value tough as anything. I used it on a canoe too!!
I knew, many years ago, a gentleman called Hal Mount, who used to write the fishing columns for the Daily Mirror, and he was trying to build a folding dinghy to paddle out to where his boat was moored. As a skin for the experimental models, he used brown paper painted both side with Colthurst & Harding rubberised floor paint, the final version was done with painted canvas
You will likely find that you have a supplier of profiled metal sheeting somewhere not too far away. Profiled sheeting is run off a roll of flat metal and is available in a range of colours finished in a plastic coating and both plain and non drip. Each profiled sheet covers 1m wide and can be ordered at your specific length, so no cutting involved.
There is one fairly close to us and last year I bought panels for a shed, black plastic coated, non-drip for £7/linear meter or sq m.
I would seriously consider that re-roofing is both cost and time effective in your case.

I've considered that. There's a profile manufacturer not far away but the price is very high - £1k+ to do the whole roof. If I did it I'd replace the roof trusses as well at the same time becuase they're full of worm; whoever built the garage did it themselves on a shoestring budget and didn't bother with treated timber. The house is full of mad decisions like that as well. Right now I just want to paint it to extend the life a few years until I can sort it out properly.

I'm not put corrugated anything back on it. Tin/steel always rusts, and anything else would be ripped off in a storm - this is NE Scotland near the coast, and the winds here can be furious. After the last storm I found a large chunk of profile sheeting in my field from a farm at least a mile away. So I'm just trying to find some paint but it's like searching for the Holy Grail it seems. :rolleyes:
I think you're after the impossible. You won't find a paint that will do a miracle cure and cost less than reskinning the roof. If it were my problem I would buy a can of the thick acrypol fibre reinforced paint, slap it on wherever you have a leak and just ignore it until you're able to fix it properly. That will buy you a couple of years at minimal expense. I've repaired an internal metal gutter in a factory with it, its still holding up 4 years on.
What's the cheapest tar you can get in a barrel,
something perhaps a bit thinner than trowel mastic, but not so thin as the many bitumen "paints" out there which is super runny and likely too thin.
I used owatrol oil and paint for my boat, boat trailer and trailer this year. I also went around the tractor and small hinges locks etc around the house with owatrol oil. This stuff goes a long way. Have a look at their range of paints
You could try Bedec MSP (Multi Surface Paint) It is meant to work on old galvanised metal. I have bought some to try on a powder coated galv roof where the paint has fallen off but not had chance to try it yet.

I have found the Bedec stuff tends to do what it says on the tin and have been happy with their other products I have used.
Our barn roof is like that.
We use black bitumen paint....although it does come in green... Lasts on an exposed site about 4-6 years & is cheapish.
You said it might be too hot in summer but at least it may be a little warmer in winter......& judging by the summer you have had in England a bit of extra warmth may come in handy.
Cold Galvanizing from Frost Auto's has always worked well on my auto restorations, I do use an Etch primer after and top coat as well.
Brantho Korrux is good paint, however if its too when applying it tends to gum up a bit. Or for a cheaper option maybe try Blackjack.
If the OP is worried about black bitumen paint allowing the roof to heat up. Then he might try a solar reflective, roof paint which is meant to alleviate this problem.
when I lived in Africa we used galv sheets a lot.......but coloured stuff was always out of stock....
so we washed the new panels with brick acid then used a Vynal emulsion paint for the clients colour of choise.......

personally I'd bite the bullet, replace the roof with insuated steel panels and the trusses.........
then u'll get at least 50 years out of it with no condensation....
on the plus side, the inside is always an off white so less elec light nec....and increase the value of ur property......
I should have stressed that the roof isn't actually leaking, I just want to give a coat of protective paint to extend its life for a few more years. I've had a few projects higher up in the backlog stack (new greenhouse, replacing my central heating...) keeping me away from it and diverting funds. If I'd had the cash to slap on a new profile sheeting roof I'd have done that already; the whole roof including rafters/trusses will need to be changed because the cowboy that put the first one on used second-hand materials including untreated wood, and the insects have had a field day. I was simply looking for something to paint on (a few hours work) to tide me over for a couple of years until I can get to this project.

Thanks for all the suggestions; my search continues.
I've recently used Bostik Flexacryl from Screwfix to overpaint a tired fibreglass covered flat roof. On a smooth surface the coverage is a lot more that the pessimistic figure on the can, but seems good enough coverage for my application given that I was over coating rather than leak repairing.
A spray product would work best. Will stretch 240%.


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If you are only looking for it to last a couple of years then an ordinary oil based paint may last that long, get a garden sprayer, thin the paint and spray it on once a year, will probably last long enough.
What you could do is spray a mix of tung oil thinned with white spirit 70/30 heavy in spirit… I’ve treated rusty metal and it holds it in a sort of arty suspended state with an ancient steel kind of look … it oxidises and coats the steel … linseed oil I have used also but doesn’t last as long .. put it on thin as it takes a while to oxidise … if you put it on thick it stays like a sticky jelly mess 🙂🤔👋 a solution if you are ok with the rusty metal look …. I have to say it looks good imho

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