Q & A

Using Cement Board Outdoors: 9 Essential Tips

Cement boards are frequently used by builders as the subfloor and wall base within a building because of their strength and durability. However, many house owners are unsure as to whether or not these boards can be used in the outdoors. When constructing the skeleton of an outdoor project, many homeowners choose gypsum boards.

Cement boards are used as subflooring and cladding for outdoor structures. If you want your installation to last, cover the unfinished area with adhesive mortar and a moisture barrier, space out the boards by 1/8 inch (0.32 cm), and caulk the joints.

Do you want to use cement boards for your outside walls and flooring? In this article, we’ll discuss the benefits and drawbacks of utilizing cement boards in outdoor settings, as well as the best way to install them on outdoor fixtures and determine if they’re right for your project.

Can Cement Boards Be Used Outdoors?

Cement boards are often misunderstood and thought to be unsuitable for outdoor use. Yes, they make a wonderful base for a wide variety of fittings, including tiled floors, kitchen counters, and interior walls. However, they aren’t just for usage inside the house. Cement boards are used to reinforce outdoor buildings made of steel and wood studs due to their durability and waterproof composition.

Cement boards don’t support mold growth, which is perhaps the biggest benefit of employing them in outdoor construction. They are not only resistant to water, but also to the growth of fungi, because their organic composition is insufficient. Because of their high water resistance, they are also a fantastic choice for places that are frequently flooded, such bathrooms, saunas, and swimming pools.

Factors To Consider When Using Cement Board on Exterior Walls and Flooring

Do you need to use a cement board basis for your outdoor structures? Among the many considerations, these are the most crucial:

Durability and Longevity

When compared to other options with a gypsum paper foundation, like blue boards and green boards, cement boards clearly perform better in terms of durability and lifetime. There are waterproof and water-resistant versions available.

However, green boards have a limited tolerance for moisture, while gypsum paper is completely unprotected against water.

Cement boards are an excellent option if you want to build an outside structure that will last for a long time and stand up to all kinds of weather. To increase its water resistance, use it in conjunction with a vapor barrier or adhesive mortar.


Cement boards aren’t the best choice if you want to keep the cost of building to a minimum. They cost more than alternatives such as gypsum paper. According to market data, a metric ton of Portland cement costs around $113.59. Gypsum paper, on the other hand, is only $8 a metric ton.

However, cement boards are superior to gypsum paper in terms of both short- and long-term cost-effectiveness and durability. Generally speaking, the latter fails to hold up as well. Gypsum paper should only be used for outdoor projects that will not be exposed to severe weather.


Cement boards are less prone to flaws and damage since they are more resilient. If you install the board correctly and give it some routine care, you shouldn’t have to worry about any serious, costly problems until after a few years have passed.

In addition, cement boards are water and moisture resistant, so you won’t have to worry as much about the growth of mold and mildew. The opposite is true with gypsum paper, which is almost entirely susceptible to moisture. Mold can begin to grow in the crevices after several years of being soaked by precipitation.

Ease of Installation

We recommend that you enlist the aid of another skilled handyman if you intend to install the cement board on your own. If we say cement boards are heavier than gypsum paper boards, believe us, you won’t be disappointed. The installation of cement boards requires more than one person.

Cement board is denser and more difficult to cut than gypsum paper, thus special equipment, including a saw and carbide blades, are needed for installation. We recommend allowing at least a day for the cement to dry.

Winner: Cement Boards

Cement boards are the superior base for most outdoor buildings due to the aforementioned reasons. They cost more and are trickier to set up. A few additional dollars may seem like a lot, but when you consider their longevity, cost-effectiveness over time, and resilience in the face of severe weather, you’ll realize that it was money well spent.

If you’re really strapped on cash and don’t care about durability, gypsum paper is your best bet. If you’re a homeowner or contractor completing a short-term outdoor structure, you probably don’t need cement’s resilience and longevity.

Top 9 Most Important Tips To Properly Install Cement Board Outdoors

Cement board installation is a simple enough DIY project that even a novice can handle it. Cement board installation on external walls can often be done by a homeowner with basic handyman skills and supplies in one to two days.

However, thorough preparation is required to ensure the longevity of your arrangement. Though it may be inconvenient at first, investing a few more hours into researching online guidelines is a worthwhile investment in order to obtain high-quality boards that will endure for decades.

Here are some of the most important things to keep in mind while installing cement boards in your outdoor space:

Use High-Quality Concrete

As a first step, make sure to get premium supplies. Some builders and homeowners attempt to cut costs by substituting less expensive materials for cement boards. Mistakes like lowering costs too much are unfortunately typical.
Keep in mind that no amount of concrete can guarantee watertightness. Although some moisture will still leak in, the amount that gets through will vary depending on the quantity of running water and the quality of the concrete.

Water damage to cement board is inevitable; unfortunately, there is nothing that can be done to prevent it. Here, high-quality concrete with enhanced resistance to water and moisture accumulation is the preferred method.

Replace Old Cement Boards

Although cement boards are long-lasting and reliable, they have a finite lifespan. Cement boards typically last for around 50 years, so if you’re rebuilding an old house with cement boards that are several decades old, it’s probably time to get rid of them and replace them with new ones.
The cement board manufacturer should be contacted to determine whether or not the fixture is still covered by the manufacturer’s warranty. The majority of cement board companies stand behind their wares with a 40- to 50-year guarantee.

Cut the Cement Board Properly

Cement board cutting is very different from gypsum paper cutting. Cement boards, to begin with, are extremely durable. A saw with a carbide tip will cut the board easily and cleanly, allowing you to trim the edges as needed. Blades with four to six teeth are what you should aim for.

Second, cement boards generate a great deal of dust and dirt. You should not work on a lawn, garden, or any other place where you wouldn’t want sawdust flying around. Power saws equipped with a dust collection system are a viable alternative here.

Waterproof the Surface Underneath the Cement Board

Cement boards, once finished, are typically impervious to water and resistant to the growth of mold and mildew. They do not, however, have a waterproof coating. No matter how little water there is, it could seep through the cement board’s pores and pool in the subfloor. The surface of the board may be resistant to fungal growth, but the area beneath it is not.
A vapor and moisture barrier should be installed to solve this problem. Water from the outside is kept out by the moisture barrier, and vapor is kept from seeping into the subfloor by the vapor barrier.

There is a difference between vapor barriers and moisture barriers. Many people mistake one for the other without thinking. However, their definitions, functions, and assembly procedures are all distinct. If you combine them, your cement board will be unstable.

The use of thin-set adhesive mortar under tiles and cement board is recommended for flooring installations, whether indoors or out.

Determine the Correct Side of the Cement Board

Lack of attention to the right cement board sections is a common error made by do-it-yourself novices. If you look closely, you’ll notice that your boards have both rough and smooth surfaces.
If you want to use thin-set mortar adhesive to waterproof your cement board, you must adhere it with the smooth side facing the subfloor. Or, if you’re using latex mastics as a vapor or moisture barrier, make sure the rough side is pointing downward.

Leave Gaps Between the Boards

A gap of 1/8 inch (0.32 cm) should be maintained between each board. To seal the joints, use thin-set adhesive mortar on the bottom and silicone caulk on top. Filling the gaps with caulk and mortar is considerably easier than manually trimming the edges of the boards, which can be highly time-consuming and taxing on the hands.

Do you feel that the thin-set mortar and silicone caulk aren’t doing the trick? Waterproof mesh tape can be used to seal off any cracks in your cement board, further increasing its resistance to moisture.

Let the Cement Board Dry Completely

Take your time setting up the system. It is important to wait until the cement board is entirely dry before utilizing it or finishing it with a coating or stucco. We recommend waiting at least one full day, or two if it’s particularly cold, for the cement to set.

The cement boards will have major long-term flaws if you use them while they are still wet. The fragility of the boards, the retention of moisture, and the resulting structural degradation are all examples of such problems. Be aware that the only way to fix these problems is to completely dismantle the setup and begin again from scratch.

Clean Dirty Cement Boards Before Finishing

Whether you’re building an indoor or outdoor space, you should always clean your cement planks before applying a finish. The integrity of your tile, stucco, or paint will suffer if loose debris is allowed to accumulate. They will come across as cheap and shoddy.

Plus, they won’t be as durable. The overall strength of the tiles will be compromised if they are adhered to a cement board that is contaminated with sawdust and other particles. Poorly attached tiles might fall off years or even months after the installation.

Polish off any loose dirt or dust from newly put cement board after smoothing down the top layer, allowing cement to set completely, and then cleaning.

However, cleaning ancient cement boards is more involved. To get rid of the obvious stains left by dirt, grab the garden hose. After that, a degreaser should be used on the more stubborn stains. Finally, wait at least 24 hours for the cement boards to dry.

Finish Exterior Cement Boards With Paint

Cement boards’ unappealing appearance is a major complaint against their use in exterior construction. The cement is rough and unpolished in appearance. They will just look like a flat piece of concrete until you cover it in stucco or tiles, both of which should be avoided for outdoor use.

Use the cement board unfinished if you’re into that kind of raw, gritty look. Painting the boards is one option for creating a one-of-a-kind, distinctive, and attractive external wall or flooring, which is what most contractors and homeowners would prefer.

Choose minimalist, monochromatic patterns to project a contemporary air. Meanwhile, individuals who wish to make a bolder impression can experiment with more vibrant hues. However, feel free to experiment with any of the many color schemes and patterns that are offered.

Painting cement boards has the added benefit of increasing their durability. These planks’ concrete, glass, wood, and other reinforcing fibers make them porous enough to absorb trace amounts of liquid. Therefore, there will be less room for moisture to seep in after the paint has dried.

Final Thoughts

Here is a quick review of the most important information for constructing a solid, long-lasting cement board basis in the great outdoors:

acquire just the finest supplies
leave a space of 1/8 inch (0.32 cm) between boards and use moisture barriers and adhesive cement on the subfloor.
Fill cracks and holes with silicone caulk.
If you are unsure about utilizing cement boards outdoors or if you lack the confidence to install them yourself, it is recommended that you seek the advice of a competent contractor. Fees will increase significantly when you bring in outside help. If you don’t know what you’re doing with a screwdriver or hammer, this is an unnecessary purchase. Avoid cutting corners on the cement board installation in order to save money.



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