Why Stucco Leaks And How To Prevent Your Stucco From Leaking

If your home doesn’t have stucco siding, odds are great you’ve certainly seen it on other homes and buildings. In certain regions, stucco is quite common and a popular choice for siding

Stucco siding is made of Portland cement, sand, lime, and water. It is typically applied in three coats over a lath base, which consists of water resistant paper, wire and other components to create the base for the cement to be adhered to.

According to a brief from the National Park Service on preservation and repair,

“Natural cements were frequently used in stucco mixes after their discovery in the United States during the 1820s. Portland cement was first manufactured in the United States in 1871, and it gradually replaced natural cement. After about 1900, most stucco was composed primarily of Portland cement, mixed with some lime.”

Stucco offers a solid, durable, and seamless house siding and provides several advantages that include natural fire resistance, good durability, and moderate maintenance (as long as leaks are not present). 

Stucco siding is also an incredible insulator against both heat and cold. A stucco exterior is relatively inexpensive and makes it easy to maintain a constant temperature in your home. Its energy efficiency is one of the main reasons stucco is such a popular siding choice in areas of extreme heat, such as the American Southwest, southern California and the valley regions of California.

Stucco, however, is not considered “waterproof” and not even necessarily water “resistant” because stucco is a very porous material. Due to its inherent permeable nature, proper flashing, weatherproofing and painting maintenance become paramount to eliminate water penetration problems. During heavy wind driven rain the water will absorb through the stucco layers quickly and you will notice after rain storms that the weather sides of the house will take hours and sometimes even days to completely dry out (see picture of south exposure after rain). 

Stucco Siding and Water Leakage

Water leakage is a common issue with stucco in areas where seasonal rain is the norm. If water gets behind stucco it will soften the areas it comes in contact with, eventually causing the stucco to break away and fall off in sheets. 

How do you know you have leaks in your stucco siding? You’ll likely see staining around the corners of windows or doors, possibly dark spots where at the roofline, and even hairline cracks. All of these are indicators of possible water damage and are signs of where water runs on or behind the stucco.

There are a few major causes of stucco failure that leads to leaks and here’s an overview of the most common problems.

Common Locations for Leaks

Windows can lead to eventual water leaks due to either improper installation that leaves minute gaps or, more likely, improper flashing. Sometimes flashing applied prior to the window being installed is heavily degraded or it’s installed on the outside of the window flanges after the window was installed. Both instances can eventually lead to water leaks.

And, sometimes, flashing is not installed at all.

Much like windows, doorways can become a source of water leaking in behind stucco siding. The installation process is similar to that for windows and they are susceptible to the same leaking problems as windows. Like windows, the flashing needs to be installed correctly before the door is installed.

Even though water leaks are most commonly found in an around the openings, the leak is rarely caused by the windows or doors themselves.  The home’s exposure, coupled with poor or inadequate flashing can create water penetration problems. For most areas in the west, southern exposures are where most of the seasonal, wind-driven rain comes from, thus where most of the window and door leaks are found.  If your stucco home is leaking, I would bet it is on the south exposure with a gable top.  

Poorly Installed Water Barrier Products

The improper installation or application of water resistive barriers for stucco such as water resistive paper or liquid products can lead to water leakage problems down the road.

Paper resistive barrier products must be overlapped horizontally and at every seam. If there is  insufficient or no overlap, water can get in behind the paper and into the sheathing or wall.

Liquid water resistive barriers must be applied according to the manufacturer’s specifications. If the product is not applied within the ambient temperature recommended or on a sufficiently clean substrate, this can lead to product failure. In addition, liquid barrier products must be applied at the required thickness, requiring multiple coats, in order to properly seal the stucco substrate.

Roof and Ground Line Issues

Wall to roof flashing can sometimes lead to leakage if it has been applied with an insufficient overlap on the wall and roof areas. This type of flashing is typically an “L” shaped strip of metal used to cover the gap between the stucco wall and the roof of a building. 

At the ground level, where the stucco wall meets the foundation, porch or patio, a type of flashing known as a weep screed should be installed.  According to wiseGeek.com,

“A weep screed is a type of building material used along the base of an exterior stucco wall. The screed serves as a vent so that the moisture can escape the stucco wall finish just above the foundation.

Without a weep screed in place, water that is absorbed through a stucco wall would become trapped within the structure, leading to potential problems with rot and mold.”

Improper installation that leaves a gap between the bottom edge of the stucco and the concrete can lead to water leakage. Simply running a wall behind a concrete patio or porch, without a wee screed, will also lead to water damage eventually.

Prevention and Remediation

The best time to waterproof your stucco siding and minimize the possibility of water leakage is before it is installed on your home. Proper installation of water resistive barrier materials, robust and properly installed flashing, and sufficient (and properly installed!) weep screeds will drastically reduce the chances of your stucco leaking.

However, preventing or minimizing water leaks on existing stucco siding is limited to a few options. 

You can paint stucco with appropriate masonry sealer products known as “silicate mineral paints” that seal out water but allow any trapped water vapor to escape. While they are largely effective, the seal will usually need to be redone every four to five years.  Painting your stucco every 5-7 years is critical because it protects the flashing and house wrap components from water absorption.  

You can apply new stucco on top of existing siding, but it is critical to take proper measures to ensure its moisture integrity. You can also apply a thin layer of new stucco silicate mineral paint waterproofing additives or other suitable water proofers mixed in. 

The bottom line is that ongoing maintenance and periodic inspections are important with stucco siding.  If you have tried re-sealing or painting the stucco and the leak is still present, we recommend that you remove the entire wall, install new windows with premium flashing and new 3 coat stucco by a reputable contractor.  

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