What do stucco and your concrete sidewalk have in common? A lot. Both are cement-based, both will soak up water, and both should generally last a very long time. However, the comparison breaks down because the sidewalk is on the ground, and the stucco is generally applied over a wood-framed house. This is where the problems can happen. In almost every remodel job I’ve undertaken where I found serious rot in the wood, you couldn’t tell from looking at the stucco on the outside that a huge problem was going to be found behind it.
Let’s examine some recent stucco failures I’ve seen and see if we can find a common theme. First, these pictures are from a 15-year-old stucco-clad and wood-framed restaurant. This was a traditional 3-coat (roughly 3/4 inch thick) stucco with two layers of tar paper on top of 1/2-inch plywood sheathing.
There was damage in multiple locations on this project, including some scuppers that leaked behind the stucco. But the most troubling rot I saw on this project was the damage found in the bottom 3 feet of the stucco closest to the ground, with no damage above. As I investigated this failure, I found that the irrigation sprinklers were wetting the stucco walls and the tar-paper weather barrier underneath could not dry out. This constant wetting without drying led to massive failure.
Here's another failure I’m working on currently. I’m replacing some wood windows on this 20- year-old home, and we again found lots of issues in the bottom 3 to 4 feet of the walls, where they meet the foundation.
Stucco can be a beautiful cladding, but, because it’s cement-based, it is porous and soaks up water like a sponge. Knowing that we can have issues with water, what’s the best path to take with a stucco installation? Easy: Use an air gap! You can add a space behind the stucco to keep it off the building by using an air-gap product that allows drainage and airflow for drying. I like using Cosella Dörken's Delta-Dry Stucco & Stone. It’s a dimple mat with a mortar screen that makes the air gap for stucco simple to achieve.
The simple change of adding an air gap behind the stucco gives multiple benefits: The reservoir cladding can dry both to the front and the back, ensuring the water-resistive barrier (WRB) won’t have water sitting against it. And if the house does need to move moisture to the exterior through the WRB, it will be able to do that much more easily.
Here’s my stucco installation step-by-step method.
1. Install a base-wall flashing. I have used a lot of peel & sticks over the years, but I also like Siga Tapes or Corsella Dörken's Delta-Flashing.
2. Install a high-quality WRB and shingle this over the base-wall flashing. Then, at the base of the wall, I install a bug screen (think steel-wool pad) and roll out the Delta-Dry Stucco & Stone. (I’m not showing it here, but you’ll want to ensure you have an air gap at the top of the stucco wall, too. This will ensure airflow behind the stucco and out the top. We used the bug screen at the top of the wall with a stucco “L” bead to terminate the stucco about 1/2 inch down from the soffit.)
3. Install wire lath as normal but with 1/2-inch-longer staples. Install the scratch coat of stucco directly onto the mortar screen of the Delta-Dry Stucco & Stone.
In the end, you can’t tell that the stucco has a 1/2-inch air gap behind it. I believe this design is a best practice for any stucco install in any climate. Using a simple product with an air gap is a game-changer for stucco and building durability.
This article originally appeared on Matt Risinger's blog.