Rust showing through Rendor

[t1mgreen]

Good evening

Approx 12 months ago i painted my rendored (external) walls and have noticed that there is a brown stain appearing through the white paint around the corners near the window
I guess that this is from rusted angle bead.

Is there a product that can be painted over this to hold this back and extend the nice clean white effect?

Thanks

Tim

 

[Zampa]

Give it a good going over with a wire brush then coat with that anti rust stuff you can use or car bodywork or red oxide primer