In FHB issue 162 Mike Guertin described flashing for cantilevered deck joists using Flexi-Tape covered with soldered copper flashing. Siding was then applied over copper. I have a similar situation, however, the siding is three-coat stucco over galvanized lath. My question is, how do prevent galvanic corrosion between the copper, the galv. lath and the mortar of the stucco.
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Don't let the metals touch. Use ice and water shield between them.
Thanks, rlrefalo. I had planned on doing that to keep the lath from touching the flashing. How about the fasteners. The stucco guy usually nails his lath up with galvanized roofing nails. I wasn't sure if this might not cause a problem if he nails through the flashing. Should I specify some other type of fastener material, keep the nails away from the flashing, or is there some other technique to use that I'm not aware of?
Ideally, the lath nails should not penetrate the copper, but if they are using stop beads, they probably will anyway. Really not an issue in my opinion. Both nail and copper will likely last the life of the stucco in any case.
Should I specify some other type of fastener material, keep the nails away from the flashing, or is there some other technique to use that I'm not aware of?
Use stainless or copper nails. If there is any source of moisture at the galvanized nails, they'll just quietly disappear where they touch the copper.View Image
Maybe this is a dumb question but, wouldn't using copper nails create the same galvanic corrosion situation where they're in contact with the lath? Maybe specifying stainless in the area around the flashing might help. Does using stainless avoid the corrosion problem? I can hear the stucco guy screaming now when I tell him I want stainless!
Does using stainless avoid the corrosion problem?
Yes.
But wouldn't the lath be lapped over the flashing. I can't imagine a situation where the lath should be behind the flashing? Am I missing something?
The lath should be isolated from the flashing with membrane or at least felt.View Image
The sequence would be Flexi-Tape, then the copper flashing (nailed to the sheathing with copper nails, then the membrane material (probably Ice Shield). The lath would then be attached over the flashing. My question is, what do I tell the stucco guy to use to fasten his lath?
what do I tell the stucco guy to use to fasten his lath?
Galv nails ought to be fine. He shouldn't be nailing through the copper flashing.View Image
Thanks, guys...I appreciate the advice.