Dry rot was found inside an exterior stucco wall, water entered through holes from rusted-out bolts that were holding up some fake shutters and trim board. 2 studs about ~1 foot and a third stud ~2 feet, along with adjacent wood sheathing are affected. The studs, redwood, are not completely rotted out, so they were sistered with new wood. Sheathing was cut back to remove as much rot as feasible. The tar paper between the stucco and sheathing, in affected area has disintegrated. During initial construction the stucco wire was probably attached to the sheathing through the tar paper. No insulation present, nor will any be installed. The original interior wall is lathe & plaster, but the repaired section will be closed up with drywall.

Building is in SF Bay, wall is south facing, so it does get exposure to heavy rainfall during some years.

Looking for an answer on if & how-to re-waterproof this exterior wall now that the tar paper gone in affected area (3 stud bays, 1-2 feet each bay). The work so far has been performed from the inside, so I am looking at the back of the stucco, with nails and wire sticking out -- new tar paper would just get shredded during install process.

I would really like to avoid replacing the stucco just to install new tar paper -- especially since the work area is second floor of building and the stucco is at max strength (~100 years old). The exterior stucco has been painted a few times. What about sealing the exterior stucco? either just the stucco without tar paper? or the section of wall inclusive of the offending bolt holes (~40 sqft)? What would be the correct type of sealer product?

EDIT, for clarification: The stucco is sound (no holes or cracks), for now, but if cracks appear in the future, without any tar paper, there could be water engress.

QUESTION: what steps can/should I take, short of re-stuccoing the area, to mitigate the lack of tar paper between the stucco and the wood? Would an exterior masonry waterproofing product provide 10+ years of protection? ie something like Dryloc or Behr Elastomeric Masonry, Stucco and Brick Exterior Paint (I have no experience with either, just products I've found during my research on this problem).

overall view sheathing cut away, tar paper rotted away


  • Tar paper is just to give it half a chance at shedding water that shouldn't ever be there. Stucco sucks in every way possible, and questions about actually doing it are few and far between, if not non-existent : diy.stackexchange.com/questions/6/… , diy.stackexchange.com/questions/4837/… , diy.stackexchange.com/questions/239814/…
    – Mazura
    Sep 10, 2023 at 22:11
  • How do I do stucco isn't a question here afaik.
    – Mazura
    Sep 10, 2023 at 22:12
  • post edited to better call out specific question Sep 10, 2023 at 22:34
  • Oh, the outside is fine, you're just looking at the inside and going, how is that supposed to work? By being water tight on the outside, without fail, ever.
    – Mazura
    Sep 10, 2023 at 22:41
  • So basically, does stucco require tar paper behind it other than to install it in the first place and what to use to keep stucco in working order. The rot remediation doesn't have anything to do with it, other than it might not be properly hung anymore on enough supports. Pictures would help.
    – Mazura
    Sep 10, 2023 at 22:49


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