Surface rust on roof

ayjay1, Jul 21, 8:41am
I have a roof to paint that has a considerable amount of surface rust on it.
I have used Black guard rust converter in the past and on one occasion the converter bled through the top coat.
If you use an oil based primer over the converter to seal it off,, they warn you that the primer might react with the converter.
Re roofing is beyond the financial ability of the elderly owner and therefore is not an option. I am hoping to do the job for the cost of the materials. To help them out. The problem is causing them a bit of stress.
I am hoping that someone might have some constructive suggestions .
Maybe the Converter might have to go?

Thank you in advance for your advice or opinions.

sanders4, Jul 21, 8:58am
Wire brush to remove flaking rust then apply cold galv primer to prevent further rusting. Follow up with undercoat then 2 top coats but never try and paint any roof when wet and cold!

tub4, Jul 21, 9:29am
I'd use a converter like Brunox as it will neutralise the rust and leave a single pack epoxy primer.
Overcoating this product is a must but a standard roof paint is fine and as said above two top coats when it warms up a little

ayjay1, Jul 21, 10:12am
Thanks for that . Cheers

marte, Jul 21, 3:07pm
You can get clear convertor now, its so the vehicle testing guys can see whats under it on cars.

tub4, Jul 21, 5:38pm
Brunox is clear, turns rust to black but still transparent & a lot of car guys use it, I really like the stuff.

ayjay1, Jul 21, 6:05pm
Who sells Brunox please?

clangie, Jul 21, 6:10pm
had the same issue with the black guard, even after 5 coats of paint on the area it bled through

golfdiver, Jul 21, 6:47pm
Its pretty clear that you do need to use an oil based overcoat on converter type products. I suppose as per your normal M.O there will be no H and S considerations OP (To help out of course) If it is Rotorua and it has considerable surface rust, have you checked under the ridge hip and penetration flashings to see if it has gone beyond saving?

tub4, Jul 22, 6:53am
I Googled it and you can buy it on line $49.85+GST from R.A.Johnstone.
About the same price as I've paid at our local auto refinish supply place.
I've had no trouble over coating with water based roof paint on my folks place down at Foxton Beach.
Edit to say you can clean your brushes with water

golfdiver, Jul 22, 7:21pm
Acrylic paint is moisture permeable and converters will fail if only overcoated with water based paint. I've learned this over a 1/4 century in this industry. Always overcoat the treated areas with oil based before painting the roof.

ajtrees, Jul 25, 7:32am
i used crc rust convertor and then put POR 15 paint over rust converter then 2 coats of solaguard.POR 15 is exspensive but it works

pete48, Jul 25, 8:51am
Water blast then 2 full coats of oil based galvanised iron primer followed by 2 coats of good quality acrylic roof paint should add at least another 10-15 years life to the roof. DO NOT go near it with a wire brush. Peter (almost 40 years in trade)

kaiser2, Nov 13, 8:55pm
You won't need to treat the rust if you use Flakaproof paint which is designed for imprefect (such as rusty) surfaces. Just paint over it. You will probably need two coats. Read the info on the label of the can.