Can anyone tell me what causes small rust spots on exterior stucco (covering a masonary wall)?
Metal corner bead or metal lath.
Random spots througout in the middle of the field would indicate moisture intrusion behind the stucco causing the metal staples that secure the lathe to rust. Pictures would be extremely helpful to help diagnose your problem.
Maybe the nails were left in place after they poured the tie beam and filled the cells.
Good catch Mike forgot about those.
Finally my years of experience as a stucco contractor may have paid off. In high school it was my after school job to prep the houses for stucco.
Knuckle buster LOL
Yeah and we used to grease the windows with old motor oil and gas. mixed in a bucket. we DIPPED A FIRRING STRIP WITH A RAG TIED ON IT AND COVERED ALL WINDOWS AND FRAMES. sorry bout the caps my finger slipped. Long before they invented Window Guard. It was nasty in the Florida heat.
Many times Rust Spots are associated with Metal Shaving from the Mixer, or Metal Shavings-Debris in the Sand from the Plant.
But Metal Shavings regardless of where they originated from are common in Cement Stucco finishes and can make a building look like hell.
Woops…forgot he said it was a masonry wall when I posted.
I see lathe on painted block homes. They use the lathe when they stucco after a home has been painted. Not that unusual down here.
Now that you have read all the reasons why—PASS it on to a stucco specialist for moisture analysis PASS the liability