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.

You can see in this cut-away picture that we had two layers of #15 felt with a traditional stucco on top.
You can see in this cut-away picture that we had two layers of #15 felt with a traditional stucco on top.

Recent Failures


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.

Extensive damage in this area was due mainly to a leak at the parapet wall cap. This is a flat roof and the parapet is the short wall at the top (which hides the flat roof).
Extensive damage in this area was due mainly to a leak at the parapet wall cap. This is a flat roof and the parapet is the short wall at the top (which hides the flat roof).

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.

See that grey sprinkler pipe in the middle of the picture? That was pointed at the wall and gave it a good soaking a few days each week. The double layer of #15 felt paper got wet and never had time (or airflow) to dry; that constant wetness led to the sheathing underneath getting soaked. Remember that in modern buildings with insulation there is no airflow inside the wall to promote drying. This wall is only 10 to 15 years old but was totally rotted.
See that grey sprinkler pipe in the middle of the picture? That was pointed at the wall and gave it a good soaking a few days each week. The double layer of #15 felt paper got wet and never had time (or airflow) to dry; that constant wetness led to the sheathing underneath getting soaked. Remember that in modern buildings with insulation there is no airflow inside the wall to promote drying. This wall is only 10 to 15 years old but was totally rotted.

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.

In this before photo, some rot is visible at the brick mold around the windows, but the stucco looks normal, with no signs of rot or failure.
In this before photo, some rot is visible at the brick mold around the windows, but the stucco looks normal, with no signs of rot or failure.
This is the bottom right corner of that window above. The terrible rot couldn’t be seen in the stucco top coat. Ugly! We also found lots of rot at the base of these window sills where water was getting in past the windows.
This is the bottom right corner of that window above. The terrible rot couldn’t be seen in the stucco top coat. Ugly! We also found lots of rot at the base of these window sills where water was getting in past the windows.

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.

Stucco Step-By-Step


Here’s my stucco installation step-by-step method.

The blue peel & stick in this picture is the base wall flashing. It will protect that vulnerable joint between foundation and framing from both water and air coming in. (Both are big trouble for a wood-framed house.)
The blue peel & stick in this picture is the base wall flashing. It will protect that vulnerable joint between foundation and framing from both water and air coming in. (Both are big trouble for a wood-framed house.)

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.

Next, the stucco metal weep goes over the top. Notice that we detailed the slab foundation on this project with a recess, or reglet, to make the stucco flush with the edge of the slab. This was designed by architect Nick Deaver, AIA.
Next, the stucco metal weep goes over the top. Notice that we detailed the slab foundation on this project with a recess, or reglet, to make the stucco flush with the edge of the slab. This was designed by architect Nick Deaver, AIA.


Install wire lath as normal but with ½-inch-longer staples. Install the scratch coat of stucco directly onto the mortar screen of the Delta-Dry Stucco & Stone.
Install wire lath as normal but with ½-inch-longer staples. Install the scratch coat of stucco directly onto the mortar screen of the Delta-Dry Stucco & Stone.

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.)

The first coat of traditional stucco is called the "scratch coat." This coat tooths into the lath and holds it onto the building. You can see here that the fabric on the Delta Dry Stucco & Stone keeps the stucco from clogging the pores of the drainage mat.
The first coat of traditional stucco is called the "scratch coat." This coat tooths into the lath and holds it onto the building. You can see here that the fabric on the Delta Dry Stucco & Stone keeps the stucco from clogging the pores of the drainage mat.

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.

Here’s the finished house. The stucco is an integral color (meaning no paint) by LaHabra. The air gap behind the stucco will ensure a couple of generations of durability. This home was designed by Nick Deaver, AIA, and built by Risinger & Co.
Casey Dunn Here’s the finished house. The stucco is an integral color (meaning no paint) by LaHabra. The air gap behind the stucco will ensure a couple of generations of durability. This home was designed by Nick Deaver, AIA, and built by Risinger & Co.

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.

For more info, visit my YouTube channel or this Cosella Dörken website.

This article originally appeared on Matt Risinger's blog.