Entryway Door
 

The metal plate(don't know actual name) above my entryway door is rusted. There is also a gap between it and the mortar. Other than letting in water does the rust and gap pose any other problem?

The gap can be easily caulked. Use a slilconized latex or a urethane caulk. The steel support can be scraped, primed with a rust reducing primer and painted.