Why Does Stucco Leak, Anyways?

There have been many instances of stucco failures and usually this will consist of leaking of some sort and it leaves a lot of people wondering what causes stucco to leak in the first place.

I wanted to write a quick rundown on some of the most common problems I have run into myself and what other contractors have experienced to give you a basic overview of what causes leaks.

Common Places Leaking Can Occur:

There are a few areas on a building that are more prone to leaking than others and this is usually due to improper installation, insufficient overlapping of materials or something simple that could have been avoided.

Windows: Windows are usually a large part of the problems that arise on stucco houses and there can be a couple of different issues that can arise. Most of the issues that I have seen in my personal experience are from improperly flashed windows.

Flashing that is supposed to be installed prior to the window being installed (bottom and two sides of window) is either heavily degraded, installed on the outside of the window flanges (after the window was installed) or is just not present at all.

Every county is different when it comes to the width of the flashing that is called for around windows but 6" - 9" is the standard for most applications and more is usually better, in this case.

Doors: Doors are pretty much the same as windows and are susceptible to the same leaking problems as windows. The installation process is basically the same for a door as it is for a window and the flashing needs to be installed correctly before the door is installed (bottom and sides).

Cracks On The Wall: I have also noticed in many circumstances that when there are cracks on a wall, it will tend to let in more water than intended, wearing down the water-resistant paper beneath the finish and base coats, resulting in water intrusion to the wooden parts of the structure.

Improper Overlapping Of WRB (Paper):

Paper Barriers: When paper is used as the water resistive barrier, it must be overlapped in a shingle fashion (horizontally) and when you have a vertical seam, there must also be overlap. It is also good to have two layers of grade D paper (10 min. or 60 min.)

When there is no overlap, or very little overlap then water can make it's way behind the paper and into the sheathing, wall or inside the building. Single ply paper does not do well either and two plys are recommended, even if you are using a 60 min. paper, for maximum water protection.

Paper for stucco is very cheap and not having adequate overlapping can lead to so many expensive problems later on down the road, it is not worth cutting corners on the main waterproofing element of most stucco systems.

Liquid Applied Barriers: WRB's that are a liquid applied product must be applied in a way that adheres to all of the manufacturer's specs. This includes things like applying the product within the ambient temperature recommended, over an approved substrate, obtaining the required mil thickness (multiple coats) and other elements in order to properly seal the substrate.

A lot of liquid applied water barriers fail for a number of reasons but from my experience it is usually due to improper installation. The two main failures are that the product is not applied thick enough which could result in small pinholes that allow water to get in or applying the material when the substrate is not clean.

Flashing Done Improperly:

Flashing that is done improperly can be detrimental to a stucco wall and will cause major issues. Flashing is more of a general term I am using and can consist of paper flashing, self adhering flashing, metal flashing, etc.

Wall To Roof Flashing: This is usually an "L" shaped piece of metal that spans the gap between the stucco wall and the roof (in most cases). I always like to use a 4" x 4" piece (minimum) to get a good overlap on the wall and roof.

Window Flashing: This flashing can be a part of the window install (usually rolled product) and can be self sticking or stapled on prior to the window being installed (bottom and sides) and on the top after the window is installed.

You will also see metal flashing on top of the window sometimes that is shaped like a lowercase "h" that goes behind the wrb, covers the top of the window and hangs over the face of the window frame about a 1/4" or so. This is used in heavy rain situations or when maximum water diversion is required or wanted.

Rolled Metal Flashing: This type of rolled metal flashing is used in many places and works great to keep out steady amounts of flowing water. This type of flashing can be found many different places and can come in aluminum and galvanized steel.

The galvanized metal is a little thicker than the aluminum and tends to last a little longer but is more expensive and more suseptible to rusting over time than aluminum flashing.

No Weep Screed Installed:

Some leaks can occur from not having any weep screed installed and in these situations this is usually resulting from a situation that allows water to sit and absorb into the stucco.

An example of this is where the stucco goes right down to the concrete and may get buried by the concrete altogether.

The picture on the right illustrates where the stucco dives directly into the pavers on the ground with no gap between the stucco and the pavers.

Water will likely seep into the stucco here and can potentially cause damage later on.

Here is an example of a properly installed weep screed on a concrete walkway where there is a gap between the bottom edge of the stucco and the concrete.

There is also metal flashing installed where the concrete meets the foundation, which goes up the wall a few inches as well.

Proper Gap Between Weep Screed And Concrete

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Check with your local county/state building codes but a good rule of thumb is to have the bottom of the weep screed anywhere from 1 1/2" - 2" above any type of surface (concrete, asphalt, pavers, roofing shingles, etc.) .

Rooflines Can Be An Issue:

Rooflines can have a lot of water running down them and if there is not kickout flashing installed, it can cause huge problems from that point on the roof, all the way down the wall!

Here is an example of kickout flashing installed on a smaller roofline that diverts the water into the gutter instead of running down the stucco wall.

It is installed behind the stucco and under the roofing shingle to get the full benefit.

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If you need to install kickout flashing on an existing stucco wall that does not have it, you will need to break out the stucco to install it properly and then have the stucco patched after it is installed.

What About Decks?

Decks can sometimes cause an issue when it comes to stucco walls leaking and the deck is not really the problem, it is the ledger board that attaches to the wall that becomes the problem.

If the stucco was not flashed behind the ledger board then problems might occur later on down the road, this is usually the case when the ledger board is installed with no wrb behind it.

A piece of metal flashing (L shaped) running along the top of the ledger board is also a good idea and something I always recommend on the ledger board too.

About the Author

The Stucco Guy

Ryan Retired Stucco Contractor

I’m Ryan, a longtime stucco contractor who has spent plenty of years getting dusty, chasing cracks, matching finishes, and figuring out what actually works in the real world. I created TheStuccoGuy.com to make stucco a little less confusing, help homeowners avoid expensive mistakes, and give you practical answers without all the fluff.

Take a look around, and if something still has you scratching your head, send me a question. I’m always happy to help.

Ask a Question About Me, Really?

Leave a Comment:

4 comments

D.S. says

This is so helpful, thank you. I’m under contract to buy a wood frame house that had stucco added two years ago during a renovation by a flipper. I didn’t know anything about stucco until I started researching it to make sure this house was properly done. I live in Florida, so we have a lot of rain and are prone to wood rot, mold, and termites if a house has bad moisture management.

There’s a roof above the front door of the house that directly touches the stucco wall, similar to the last photo in this article. It has no flashing that I can see, and no gutter. And I need to get a closer look, but I believe that on the side of the house with the driveway, the stucco goes all the way down and meets the concrete with no drainage gap or weep screed.

Sadly, I may have to walk away from the house if the stucco is likely to lead to water damage down the road. I’m glad to have all this information to help avoid making a costly mistake.

Mike M says

I am talking to a few contractors about replacing vinyl siding on my home with stucco. This seems to be a very popular upgrade in my area. I am asking them to explain to me how they are going to flash the existing windows but they don’t want to go into any details. There seems to be a lot of material online on flashing new windows in stucco walls or installing new windows into old stucco walls but I can’t find anything about flashing existing windows when adding stucco around. I see many houses around where it was done, so it must be possible to do properly but I would like to understand what the proper procedure is so that I can ask contractors the right questions. Thanks.

Albe LaFave says

Which system is better over framing, dura rock with synthetic top coat or three coat traditional system (perhaps with synthetic top coat)? Are the advantages of the liquid (Sto Gold Coat) coating significant enough to outweigh the cost over good old 30 lb felt as underlayment? I am looking for durability, second to cost!

I have heard that metal lathe can rust away over time or leave rust stains on corners, etc. If that is an issue, what is the best lathe to use?

The Stucco Guy says

Durability is usually a lot of $$$ when it comes to stucco. There are many options out there that make the process more durable but equate to more materials, more time, more labor and more money. There is also fiberglass mesh that works well for lath (spiderlath).

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