How to treat rusted metal shed roof?

[Cranswick]

Hi l have some rust on my shed roof, not sure what exact metal is , some sort of corrogated steel, its silver color, When l paint it

with Dulux Metal sheild rust primer ( Below) does it matter if l paint over some of the rust and theres still rust on the roof underneath the primer, will this primer kill or convert the rust underneath? so when l paint on top the rust underneath wont grow back. ALso is Dulux metal sheild the best primer to use if l also want to kill the rust or is there a better one

[MitchellMc]

Hi @Cranswick,

You should start by removing as much loose rust as possible with a wire brush and mechanical means. Once the majority of rust is removed, the more, the better, you can apply the Metalshield primer. The primer can be applied over hard to remove rust sections, and sealing it off from moisture will prevent it from progressing further.

You can read more about surface preparation and application on the Dulux product page.

• Surface preparation: Remove any loose, flaky rust by scraping, sanding with p320 sandpaper or wire brushing. Use Mineral Turpentine to remove all grease, oil and rust residues and allow to completely dry prior to priming.

• How to apply: Shake the container for 15 - 20 seconds before opening. Pour contents into a plastic container or roller tray. Apply 1 or more coats of Metalshield Rust Primer™ by brush roller or air spray to a suitably prepared surface. For best results apply Metalshield Rust Primer™ immediately after surface preparation is completed. Metalshield Rust Primer™ will darken wherever it is applied over rust. Metalshield Rust Primer™ must be overcoated within 7 days. Application and drying temperatures MUST be above 10C.

Please let me know if you have any questions.

Mitchell

[Cranswick]

Apart from Delux metalshield primer is there another brand of primer or product l can use that might be more effective in killing the rust, perhaps use white knigh rust converter , rannex bustbuster, or white knight primer, or is the Dulux products just as good

[MitchellMc]

The Metalshield primer is the way to go, but you can treat the rust before using the primer @Cranswick. Follow the prep instructions above, then apply a convertor such as White Knight 0.125L Rust Guard Rust Converter or Bondall 250ml Ranex Rustbuster Rust Converter. Once dry, you can apply the primer over the area.

The converters will better transform the rust into a stable material, preventing it from continuing to corrode. However, the primer should still be applied over the area to block out water access, which is the root cause.

Mitchell

[Cranswick]

thanks, yes after l sand the steel beams if l treat it with rust converter it would be more effective but it would also be more expensive and time consuming becasue theres meters of steel beams under my house. If l skip the rust converter and just apply the metalshield primer and theres still some rust underneath would the metal shield primer most likely kill it or stop it from growing. l think l read the metalshield primer has some rust killing or rust converting elements in it ? is that correct? so perhaps the rust converter wont be necessary and l can just apply the metalshield primer over the sanded beams? 

[MitchellMc]

The Metalshield primer is designed to inhibit the rust from continuing to get worse @Cranswick—rust forms when moisture contacts steel. If you paint the steel, then it prevents moisture from contacting it. So, by applying the primer, you'll inhibit the rust's growth. A converter changes the rust into a different form and helps stop it from eating away the metal. The primer helps prevent further rusting but isn't as good as a convertor. However, either of the options should do a reasonable job at stopping the rust from growing.

Mitchell

[Cranswick]

if l use a rust converter which one is better, rannex or white knight rust guard converter or are they both the same?  also are both totally safe for the steel, is there no risk they can corrode or harm the steel?

[MitchellMc]

Hi @Cranswick, 

They are all designed for steel and won't harm it. I've used both the White Knight 0.125L Rust Guard Rust Converter or Bondall 250ml Ranex Rustbuster Rust Converter, and both work perfectly well. If you need to choose, I'd go with the White Knight product.

Mitchell

[Cranswick]

l am not sure if the steel beams were galvanized , but l think l read Rannex should not be used on galvanized steel as it damages the protective galvanized coat, is white knight rust converter safe to use on galvanized steel compared to Rannex

[EricL]

Hello @Cranswick 

You're correct, Ranex is not ideal for galvanized steel. The White Knight rust converter site only mentions that it is effective on the rusted areas only. Allow me to double check for you. Once I have more information, I'll get back to you.

Eric