We have one south-facing stucco wall that is about 8 inches below grade. Just dug out this area to replace the drainage pipe that runs parallel to the wall and drains rainwater from downspouts out to a swale. Had an independent building inspector inspect the wall. There was no damage or termites. The area cannot be graded because the home is built on a slope. We really have no choice but to re-fill after the drainage pipe replacement is finished. Our plan is to sandblast the paint off the stucco in a stripe that will leave several inches of untreated stucco above grade to release any wicked up moisture out into the atmosphere. There is a great deal of radiant heat at that wall, so moisture should not be a big issue even with being below grade. Now here is where we are stumped. Do we do something to the bottom of the wall to protect the weep screed (like lay a row of bricks next to it) before filling back with the dirt? The builder had a piece of wood running along there between wall and drainage pipe which we removed because it was so old and rotten. Surprisingly, there was no insect activity in the wood. The building inspector could see no reason for the wood being there other than to stablilize the drainage tube when dirt was back filled. Would greatly appreciate any ideas/suggestions/information regarding how to proceed with a below-grade stucco wall (by the way, this is the real stucco, not the synthetic stuff).

The weep screed is primarily a flashing element, but to be most effective ther has to have ready access to outdoor air at that level to ventilate the gap between the stucco and the structural wall to allow water vapor as well as liquid water to escape. Hard stucco is quite porous and will wick up & store a surprising amount of dew and rain water. When the sun hits rain/dew wetted stucco the stored moisture is driven off a ferocious rate in both directions- into the cavity as well as to the exterior. But the sun warmed stucco also induces a significant stack-effect force on the cavity space that would induce a convection flow, if the cavity is vented to outdoor air at both the bottom & top. Allowing it to convect removes the water vapor that was headed for the interior by replacing the humid air with drier outdoor air, but if convection is blocked, some of that moisture inevitably ends up in the interior wall structure putting it at higher risk for mold, etc.

Back filling the 8" with pea gravel or half-inch screenings would likely give you reasonable air flows despite the screed being below grade. Check to see if the stucco cavity is vented at the top too- if not drilling in a few vent holes under the eave/rake of the roof isn't a bad idea.

The paint is likely to be at least semi-permeable to water vapor, even if it's nominally waterproof to liquid water (if it isn't semi-permeable it's likely to blister & fail). There's probably little benefit to sandblasting the stripe of paint off, especially if the cavity is set up to convection-vent.

Posted By Dana1 on 06 Aug 2012 04:45 PM
The weep screed is primarily a flashing element, but to be most effective ther has to have ready access to outdoor air at that level to ventilate the gap between the stucco and the structural wall to allow water vapor as well as liquid water to escape. Hard stucco is quite porous and will wick up & store a surprising amount of dew and rain water. 

What about EIFS? Is that also porous like hard stucco? I kind of like the look of EIFS better than traditional stucco, it also seems more durable than traditional stucco.

Does EIFS on an ICF wall require chicken wire like traditional stucco does?

All good building practices start with keeping the structure and siding dry!
I have a similar situation at my house where the grade drains toward the house. I dug out along the house to a depth where there is several inches of foundation showing, installed an underground drain with a flat surface of washed stone next to the house, then built a graded embankment a couple of feet away from the house which helps to divert the water, or at least direct it into the drains. You could do the same with pressure treated beams or cement blocks. Burying the house in the grade is a recipe for disaster, and while you've been lucky so far, your luck may not continue. Get the siding out of the ground and keep it dry.

Lbear: EIFS systems typically come in under 5 perms and over 1 perm, so they're essentially class-II vapor retarders. They're non-wicking and will not store bulk water.

But they impede drying toward the exterior somewhat, making it more vulnerable than vented claddings to any bulk-water incursions that get by the siding. In practice EIFS has a pretty lousy track record for handling bulk water loads, and requires perfect installation and regular maintenance to really do the job, particularly in rainy climates. In Vancouver B.C. many condos were built using EIFS during the '80s & '90s, and the local press coined the term "leaky condo problem" (google that exact phrase) in reference to they myriad EIFS failures. Whether due to poor implementation or lack of maintenance, EIFS clad problem-buildings are not rare.

But that's not to say the system doesn't work if it's done right and maintained regularly- only that it isn't as resilient to construction error or benign neglect as most other siding systems.

Hard-coat stucco is pretty good if properly vented, but can cause rot issues in wood-sheathed stick-built houses in some climates & conditions if venting & drain issues are ignored due to it's moisture-reservoir characteristics. (In that regard it's not too different from other masonry-cladding systems such as brick-veneer, etc., which work best with a vented cavity between the cladding and structural wall for moisture control.)