What you need to know about stucco

Stucco is one of the oldest forms of wall cladding in the residential and commercial construction industry. Stucco usage dates back as far as Ancient Greece— over 1000 years ago. Stucco provides a nice smooth finish, giving walls an appearance of a perfectly smooth, seamless look that many homeowners desire. As many of you know, stucco has had it’s fair share of problems, but that can be said about almost any building material in the construction industry. But for some reason, it always comes back to stucco when people begin to talk about problematic wall cladding that leads to moisture damage.

Stucco comes in a variety of different types, but most all contains the same key ingredients: a mixture of Portland Cement, sand, and water. Many stucco mixtures contain lime, admixtures, and/or fibers. Thousands of years ago, the most common way to install stucco was over masonry walls. It was durable, water resistant, had a long life, and had a great appearance. Today, stucco installed over masonry is less and less common, but it still one of the most effective ways to install stucco, and has significantly less problems— it is almost problem free to be honest. The problems with stucco in residential construction, is that it is installed over wood framing and sheathing, which can lead to significant problems if water gets behind stucco. Proper stucco installation requires time and effort. It requires very careful detailing by the contractor— something in which in this day and age is harder and harder to come by. If not properly installed, you can almost guarantee that water will get behind stucco, which can eventually penetrate the structure, causing a high potential for rot and mold development. Proper stucco application also costs a bit more to do correctly. As many of you know, cutting costs is king when having a profitable business, and while every builder and business owner tries to cut costs in every way possible and still maintain a good product, stucco is not the area that you want to cut costs in.

Stucco has some pretty straightforward requirements regarding it’s installation. The building paper over wood backing must be Grade D and have two layers. The reason for 2 layers is that the stucco bonds to whatever it is applied to, so if there is only one layer of paper, the stucco bonds to that and no longer has a drainage plane protecting the wood structure. A proper weep screed is required at the foundation, which allows for proper drainage if water does get behind the stucco. The metal lath and accessories must meet specific requirements as well. And lastly, as mentioned before, stucco application takes time and careful detailing. When builders are under pressure to complete construction projects on schedule, sometimes the proper time to install stucco is cut short.

So what are some of the main problem areas with stucco when it is improperly installed?

The first problem is lack of drainage. All vertical panels of stucco have to drain water at the bottom. There needs to be a weep screed at the bottom of all wood framed walls with stucco cladding, and this has been an ASTM standard for a long time, and has rarely been followed. Without proper drainage, when water gets behind stucco, it has nowhere to go, so it just sits and destroys the wood framing beneath the stucco. Another area that requires proper drainage is where vertical walls transition to horizontal returns, such as a soffit, the underside of a balcony, in between columns, etc. There is rarely, if ever, proper drainage installed in these areas. I inspected a new construction home last week that did not have proper drainage in this area, and I will be the first to tell you that it is not fun having to explain to the homeowner that something on their brand new house is not installed correctly. Drainage at horizontal returns is specifically required by ASTM standards, because any water that gets trapped in these areas will literally sit there forever, and rot away whatever wood in underneath. Many times, the underlying damage that water can cause beneath stucco isn’t even remotely visible— the outside of the stucco looks fine, but underneath is a world of damage.

Another problem in stucco installation is that it is installed with too thin of a coat. Stucco is required to be at least 7/8 inches thick, exclusive of the texture. Stucco that is too thin is more susceptible to cracks, and cracks let water in, and that is bad. Once the wire lath underneath the stucco starts rusting, it expands, pushing outward on the stucco, creating more cracking, and letting more water in. A snowball effect that you do not want on your walls.

Another way cracks can develop in stucco is where it meets dissimilar materials. Anywhere that stucco meets a dissimilar material, it requires a casing bead to be installed. A casing bead provides a gap between the two materials that should be caulked, and the casing bead provides an alternative material for the stucco to bond to, rather than whatever else it is up against. When casing beads aren’t installed, cracks are very likely to develop as the dissimilar materials expand and contract against each other. One of the most common areas for stucco to crack and cause problems is at windows, and this is due to lack of a proper casing bead. If you have stucco around your windows, and notice on the interior walls that there are some slight moisture stains, chances are what is beneath the wall has had some serious water intrusion damage.

Other problems with stucco installation include: improperly installed control joints and improperly installed paper backed lath. In order to install the paper and the lath correctly, the paper must be lapped over the paper, and the lath must be lapped over the lath— both of which take time and detail. If paper is lapped over the lath (wire), thin spots are created, which are very prone to cracking. If you ever see stucco with some long, horizontal cracks that are very uniform in distance apart, then this is likely your issue— and there is not a repair method for it other than completely redoing the stucco. If you ever look at stucco on large exterior wall surfaces, hopefully you notice that there are joints every so often. These joints are there for a reason: to allow stucco to shrink initially, then expand and contract. The key at these joints is to properly cut the wire lath and properly position the paper in a way that the stucco can lock onto the joint. If not done correctly, cracks can develop, which defeats the entire purpose of installing the joints to begin with.

If you suspect that your home has stucco damage, it is important to call someone who specializes in stucco inspection, not the contractor who installed your stucco to begin with. Visible signs of stucco problems are moisture stains on the interior walls and exterior wall cladding, particularly around windows and doors. Any cracks should be sealed immediately upon noticing them, no matter how big or small. The only way to definitively diagnose stucco damage is through destructive testing, where pieces of stucco have to be removed to see what sort of damage is beneath them. Stucco repairs are expensive, especially when structural material replacement is involved. If you are considering buying a home with stucco, make sure you hire a home inspector who has knowledge in stucco installation, and knows what to look for to identify problems. Fortunately, not all stucco is installed incorrectly, and there are many builders out there who do a tremendous job in proper installations, so this blog post is not intended to scare you away from buying a home with stucco, just make sure you are aware of what the problems are and it is inspected accordingly.