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Stucco: Failures & How to Do it Right!

 

 What does 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.  Almost every remodel I’ve undertaken where I found serious rot in the wood, you couldn’t tell from looking at the stucco on top that a huge problem was going to be found underneath 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 ¾” thick) stucco with two layers of tar paper on top of 1/2″ plywood sheathing.  

You can see in this cut-away picture that we had two layers of #15 felt with a traditional stucco on top.
Tons of damage under this area. This was mainly due to a leak at the parapet wall cap. (this is a flat roof and the parapet is the short wall at the top that 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 of the rot I saw on this project was the damage found in the bottom 3’ of the stucco closest to the ground, with no damage above.  As I investigated this failure, I found 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 of the week. The double layer of #15 felt paper got wet and never had time (or air flow) to dry and that constant wetness lead to the sheathing underneath getting soaked. Remember that in modern buildings with insulation there is not any air flow inside the wall to promote drying. This wall is only 10-15 years old but was totally rotted.

 

Let’s look at 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 3-4 feet of the walls where they meet the foundation.  

Before photo. Some rot visible at the brick mold around the windows, but the stucco looked normal with no signs of rot or failure.
This is the bottom right corner of that window above. Terrible rot that 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.  So, knowing that we can have issues with water, what’s the best path to take with an installation?  An air gap!  If we add a space behind the stucco, keeping it off the building by using an air gap product, that allows drainage and air flow for drying!  I really like Dörken DELTA®- DRY STUCCO & STONE for this air gap.  It’s a dimple mat with a mortar screen that makes this air gap for stucco simple to achieve.  

This simple change of adding an air gap behind the stucco gives multiple benefits.  This reservoir cladding can now dry both to the front and the back, ensuring your 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 Dörken DELTA®-FLASHING works great, too.  

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 the wood framed hosue)

 

#2  Install a high- quality water resistive barrier (WRB) and shingle this over the base-wall flashing.  Then, at the base of the wall I install a bug screen (think brillo pad) and roll out the Dörken 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 air flow 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 ½” down from the soffit.)


Next, the stucco metal weep goes over the top.  (notice that we detailed th 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.).  


#3  Install wire lath as normal but with ½” longer staples.  Install scratch coat of stucco directly onto the mortar screen of the DELTA® -DRY STUCCO & STONE.

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 holds the stucco from clogging the pores of the drainage mat.

 

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 generations of durability! This home was designed by Nick Deaver, AIA and built by Risinger & Co. Photo credit Casey Dunn.

 

 As you can see the finished house is beautiful and you can’t tell that the stucco has a ½” air gap behind it.  I truly believe this is a best practice for any stucco install in any climate.  This simple product with it’s air gap is a game changer for stucco and building durability.   

 For more info visit my YouTube channel or this Dörken DELTA® website 

Best,

Matt Risinger

Risinger & Co

Austin, TX