Iron stains on new painted pebble dash? Pic

[slumbalumba]

I have a new extension, externally insulated & rendered with painted pebble dash to match the existing. We now have several 'bleeding' iron stains - see pic. I don't want to dig out the affected areas as I don't want to risk hacking at the insulation underneath. If I thoroughly coat the area with a quality exterior stain-block & repaint, will that be enough to stop the stains reappearing?