There are two reasons why you may be interested in installing Stucco over foam board. The first is because you like Stucco’s versatile finish, which is a durable and low-maintenance material. Secondly, you want to increase the R-value or insulation of your home using foam.
Stucco over foam is professionally known as the exterior insulated finish system (EIFS). In some parts of Nevada and California, it’s referred to as the one-coat system.
This system is used in many older homes. However, over the years, it has been considered controversial due to its many associated problems.
Installing Stucco over foam isn’t the standard insulating or finishing a home’s exterior method. As a result, you can expect many issues to arise from such a setup. In the post below, we will discuss some common problems of installing Stucco over foam.
1. The Weight of the Stucco Can Pull the Foam Board from the Walls
Stucco weighs around ten pounds per square foot. Can you imagine how heavy it will be once attached to a foam board?
Even if you use nails and adhesives to attach these two, there is a good chance that the weight of the Stucco will overpower the foam board, and both materials can easily fall from the wall. Using Stucco over foam is a recipe for failure.
2. Adhesion Will Be a Problem
If you thought weight was the problem, wait until you read about adhesion. How do you intend to bond Stucco to foam? Will you use mortar? Probably not. In such a setup, you will be forced to use longer nails and strong adhesives to hold these two together.
There is a high probability that these two may not work. Therefore, you may be tempted to add a metal lath to reinforce the structural strength. By adding a metal lath, you increase the structure’s weight. As you may have guessed, that will also lead to failure.
3. Cracks will Form on the Stucco
If your EIFS system is weak, cracks on the Stucco will be inevitable. Although Stucco is a durable material, it must be installed on a structurally sound surface. We can all agree that a foam board is not a structurally sound surface.
4. Mold will Develop on the Foam Board
Is Stucco waterproof? This has been a hot topic of debate for the past few decades. We won’t go much deeper into this. However, research shows that Stucco can let moisture pass through.
If you Stucco over foam, water will eventually get into the foam board, and the dampness will create a breeding ground for mold. The day you consider tearing down your wall, you will find a mold infestation.
5. It’s Not a DIY Project
You can use the DIY approach for many building projects as long as you have the knowledge and tools. Unfortunately, this isn’t one of them. Laying Stucco over foam may seem easy. But it’s a job best left for professional contractors with a warranty.
As mentioned earlier, the EIFS system is known to be controversial because of the high risk of failure. Therefore, if you go ahead and install Stucco over foam, then it fails, and the repairs will be expensive and time-consuming. Therefore, this isn’t a construction project that you can Do-It-Yourself.
If you must install Stucco over foam, ensure that you hire a reputable company that follows manufacturer instructions and has a warranty just in case anything else goes wrong. Even when installed by experts, there is much room for error.
6. Moisture Damage
If you thought that mold development on the foam board was the only effect of water damage when you Stucco over foam, you are in for a huge surprise. As moisture penetrates the Stucco, it goes past the foam and reaches the wooden framing.
As you already know, wood is highly vulnerable to water and may start to rot when exposed to long-term dampness. As the wood rots, so will the sheathing. Eventually, you may end up with a rotten house structure.
7. It Makes the House Exterior Vulnerable to Minimal Impact
When applying Stucco over foam, you must ensure that the space between these two materials is negligible. Since the system will be thinner than usual, the exterior of your home will be quite susceptible to impact. The surfaces can easily get damaged from a minor impact of a ball.
With the above in mind, you can picture how long such a setup will last, especially if you have kids.
8. It May Affect the Market Value of Your Home
After reading all these issues, would you be interested in buying a home with foam behind the Stucco? That’s what installing Stucco over foam does to your home’s market value.
When you decide to sell your home, many buyers won’t be interested in your property because no one wants to deal with these issues.
Is There a Way to install Stucco Over Foam and Avoid These Problems?
As mentioned earlier, Stucco over foam board isn’t a conventional way of insulating or decorating your home’s exterior.
If you want to enhance insulation, you should spray foam into the wall cavities. As for decoration, you should install the usual three coats of Stucco on a structurally sound surface.
However, as we all know, every project in the construction industry has some loopholes. If you wish to install Stucco over foam, here is how you can do it correctly and avoid the above problems;
• First, I would advise you to use rigid foam boards. There are many types of foam you can use before Stucco. Examples include XPS and EPS. However, Polystyrene foam boards are more rigid and repel water much better than their counterparts.
• The foam board you settle for should be installed over plywood firmly nailed onto the studs. The reason behind this is to create a structurally strong surface that can accommodate the weight of the Stucco.
At the same time, a plywood sub beneath the foam board will prevent movement that may lead to the cracking of the Stucco. The foam board should be glued using a strong adhesive.
It may be tempting to choose a thicker foam board to get a higher R-value. But please stick to a foam board that’s at least one inch thick.
• After installing the foam board, you should apply a weather-resistive barrier. I’m not talking about the mat barrier but the liquid ones.
Liquid weather barriers are the best option here because they won’t increase the walls’ thickness, nor will they add more weight. The purpose of a weather barrier is to prevent the passage of moisture and air from the Stucco past the foam board.
• Please don’t install the Stucco directly over the foam board. Cover it with building paper. There are two reasons you should use building paper between Stucco and foam.
One is to pass most local building codes. Secondly, the building paper acts as a drain plane. If you live in an area that rains a lot, the building paper will enable water to easily pass through without reaching the foam board behind.
• From there, you can apply Stucco and let it cure.
These steps are the ones that a professional contractor should also follow. If they have another method, ensure they explain each step’s importance.
You will have more peace of mind dealing with a contractor with a warranty. Also, whether you should or shouldn’t use a metal lath will depend on the thickness of the foam board and Stucco.