Addressing rust spots on a stucco home

cacalves asked 7 months ago

I own a home in San Francisco whose stucco is showing random rust spots. At first I thought that the stucco was not thick enough and/or the lath or fasteners were not of the proper type but now I am more inclined to believe that iron specs contaminated the sand used at the stucco material (there was a class law suit against a local sand supplier a few years ago because of this type of contamination, I was told).

I want to repaint the house and would like to make sure that I take all the right steps to make sure that the rust spots do not come back after the paint job.

I am considering using F-9 Barc and/or Rusterizer to attack the stains at first and then using two coats of a good quality primer followed by two coats of an elastomeric paint.

Has anyone at this forum faced a similar situation and what solution did you find? I would appreciate any opinion on my approach as well.
Thanks.
Cassio

1 Answers
MagicDave answered.

If the rust spots appear “randomly” rather than uniformly as you claim, then maybe you are correct in believing that the stucco material was contaminated… nevertheless you really should prime ALL of the stucco using an Exterior Oil Base Stain Sealer Primer, to insure that “new” spots do not appear… 1 coat applied generously should be enough but 2 coats might be better, then top coat with a good quality brand, like Sherwin Williams, Exterior Acrylic House Paint, 1 coat applied generously, using a flat finish on stucco is best… Good Luck!
In your predominately humid area, plan on getting a repaint on your exterior every 7-8 years…

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