One of the biggest challenges builders face is installing tiles in wet areas. Sometimes you install the tiles, and after a few months, they disengage, then crack and break. When you analyze the situation further, you realize it is due to the moisture. The underground water rises through the concrete slab, wetting the adhesives and later floating the tiles. These tiles become more vulnerable to loading, leading to breakages.
This problem can be solved by proper substrate selection. While there is a range of substrate sets to choose from, engineers have demonstrated that concrete boards are more suitable for wet areas. These boards are not only used for tile installation but are also found in bathrooms and shower enclosures. Industry professionals sometimes use them as an essential tiling underlayment system. But what are cement boards?
Cement boards are made from a mixture of cement, reinforcing fibers, and special mineral additives. Compared to gypsum boards and plywood, these boards are more durable and can withstand harsh environments, including fire, impact, and moisture. Thus, engineers prefer to use them in wet areas and exterior applications.
How are cement boards manufactured?
The manufacturing process for these boards starts with mixing the slurry. Here, the raw materials, containing 90% cement and sand, 7% fiber, and 3% water, are mixed to form a slurry. Common fibers include wood pulp or cellulose. The slurry is then rotated in mesh-covered cylinders to drain away water. This forms thin cement fiber. These thin fibers are then layered in the moving felt belt to achieve the desired thickness. After this layering process, the resulting layered sheets are pressed under rollers to remove excess water, compressing the material into a single, dense sheet. The production of these boards is fully automated using advanced industrial processes. The materials are then cut into different sizes and cured to harden them.
What are the desirable properties of cement boards?
The ability of cement boards to withstand extreme residential conditions makes them highly preferred over other board types, such as gypsum and plywood. These boards are more durable, water-resistant and have high dimensional stability. Further, the boards rarely support mold growth due to moisture. More importantly, these boards are fire-resistant, making them suitable for both interior and exterior applications.
Why Do Builders Use Cement Board?
The properties cement boards have make builders prefer them over other boards.
Moisture Resistance
Cement boards offer exceptional moisture resistance, making them suitable for water-prone environments such as showers, laundry areas, and commercial kitchens. The water in these areas penetrates through the tiles to the substrate. If the substrate is made of traditional materials like wood, it absorbs water. This results in swelling and warping. Further, the substrate’s structural integrity is compromised. The composition of the cement board does not support high-rate water absorption.
| Material | Water Absorption | Swelling Risk | Dimensional Stability |
|---|---|---|---|
| Plywood | Moderate-High | High | Moderate |
| OSB | High | Very High | Low |
| Gypsum Board | Moderate | Moderate | Moderate |
| Cement Board | Low-Moderate | Very Low | Excellent |
Superior Tile Support
A good substrate must resist compressive and flexural loads. Without these features, ceramic and porcelain tiles can experience movements that lead to cracking. Further, these movements cause water infiltration. Cement boards have high compressive strength and good flexural rigidity. These features make them resistant to impact and remain stable during fastening.
Mold Resistance
Mold is undesirable on construction sites due to its impact on structural integrity. In a moist environment, mold and high humidity can accelerate metal corrosion. It affects plumbing running through the substrate surface and other structural steel. For mold to grow, it requires a combination of water, oxygen, organic material and a favorable temperature. During plumbing and wiring processes, pipes are insulated with materials that can later provide nutrients for mold. Further, some other boards, such as plywood, provide suitable environments for mold growth. On the other hand, the composition of concrete boards does not provide mold with food.
Fire Resistance
Cement boards, unlike wood-related boards, are non-combustible. Beyond the fire triangle principle, cement boards help reduce the rate of fire spread throughout the rest of the house. When fire meets cement board, the cement matrix absorbs thermal energy from the fire. This thermal energy evaporates the internal moisture in the cement composition. Effectively, the cement boards slow down the heat transfer rate.
What are the common applications of cement boards?
These boards are more durable and water-resistant, making them more widely applicable. The boards are used in exterior cladding systems. Engineers use these boards for exterior sheathing and cladding, which offer numerous benefits such as resisting rain and humidity, supporting facade finishes, maintaining dimensional stability, and reducing maintenance requirements.
The boards are also used as tile backing systems. Due to their water-resistant properties, these boards are used to reinforce tiles, preventing tile failure.
Application in Bathroom Showers
Bathroom showers are among the building’s wet areas that require special attention to keep the house structurally sound and healthier. Beyond constant water flows and humidity, the bathrooms have cleaning chemicals. This environment can accelerate deterioration, especially if the surface is made of metal boards or wood boards. Unlike these alternative boards, cement boards do not soften when exposed to water because they do not absorb water.
Application in Bathtub Surrounds
Compared to bathroom showers, bathtub surrounds are not continuously subjected to water spray. However, it is exposed to daily water and soap residue. The temperatures around the bathtubs keep fluctuating due to alternating hot and cold water. This environment requires a substrate with stronger adhesion, moisture resistance, and structural integrity, all of which are provided by cement boards.
Application in Tile Flooring
Cement boards offer rigidity and dimensional stability, which are critical in tile flooring substrates. A rigid substrate can withstand tile loading without breaking. If you use a weak substrate, however strong the tiles are, they will dislocate, break or buckle. Choosing a poor substrate or setting it poorly can lead to movement, causing tile swelling and, subsequently, cracking. Concrete board provides a wider, flat surface for even distribution of tile loading. Floors are subjected to various types of dead loads, live loads from occupants and furniture, vibrations in commercial buildings, and thermal movement. A structurally stable cement board can support this loading and uniformly transfer it to the foundation.
Application in Kitchen Backsplashes
The water and moisture levels in the kitchen are lower than those in showers. However, even with small moisture levels and temperature gradients, the environment can be unfavorable for some wall materials. In the kitchen, the walls are exposed to steam from cooking, cleaning chemicals, water splashes from the sink, and temperature changes. These walls require a reliable substrate, such as cement boards, to prevent wall tiles from moving. Further, cement exhibits reasonable thermal expansion, making it suitable for kitchen applications. The kitchen environment experiences localized heating from activities such as ovens and dishwashers.
What are the limitations of cement boards?
Despite their many strengths, cement boards also have limitations that make professionals in the construction industry sometimes skeptical about their use. First, the boards are relatively heavy compared to gypsum and plywood. This leads to higher transportation costs, increased labor requirements for handling, and slower installation. Second, the boards are more difficult to cut and install. It requires specialized cutting tools, which may be costly. The cutting generates dust, thus necessitating the use of personal protective equipment (PPE). However, the performance benefits of these boards make it easier for engineers to navigate these challenges, leading them to choose them over other types of boards.
How Do You Install Cement Board Correctly?
The methods for installing cement board include preparing the subfloor, cutting backer board, securing it, and sealing joints.
Prepare the Subfloor or Wall
Imperfections in the subfloor can cause stresses that are transferred to the cement board, leading to tile destruction. If the subfloor is not well prepared, it can cause cracked grout joints, moisture penetration and backer board movement. Preparation ensures surface flatness, structural integrity and load-bearing capacity. Cleaning involves removing dust, dirt, oil, grease, and loose mortar, among other unwanted materials. All contaminants must be removed, even if they are too small to detect. This helps maintain the bond strength.
How Do You Cut Cement Board
Proper cutting of cement board helps save materials and reduces installation time by ensuring the panel fits well. Cutting cement board requires the greatest care because of its brittleness. To cut this board, installers should first score the surface. They then snap the board along the score line. Cutting these boards generates dust that must be controlled for health reasons. Dust can be controlled through wet cutting systems, HEPA filtration, or vacuum extraction. If these technologies are unavailable, installers can choose outdoor cutting stations.
Secure a Cement Board
The third step of installing the board is securing it. Installers secure the mechanical connection between the board and the supporting structure. Cement boards are not meant to function independently; rather, they require fasteners to form a composite. In this composite, the board serves as the substrate. Proper fastening is required to secure the board, prevent tile cracking, keep the board in place against movement, eliminate surface unevenness, and prevent grout joint failures. Unlike other boards that use standard screws, cement board requires specialized, corrosion-resistant fasteners to ensure long-term integrity. Proper fastening ensures that the load is transferred effectively to the subfloor. When a person walks on the tile surface, the load is transmitted to the thin-set mortar that binds the tiles to the board. The mortar layer transmits the load to the cement board. The board absorbs this load and then transfers it to the fasteners. If the fasteners are poorly set, they can crumble, leading to board shearing and effects transferred to the tiles. The fasteners later transfer the load to the subfloor and then to the structure’s foundation.
Seal Joints
The last process the installer undertakes is sealing the joints. When installing cement boards, installers leave small gaps between panels. These gaps allow installers to adjust any dimension and make changes before installation. These reinforcements are necessary to prevent the build-up of stress concentrations. Unsealed joints contribute to cracked tile surfaces and grout lines, allowing water penetration.
What Mistakes Should You Avoid When Using Cement Board?
1. Skipping Waterproofing
While cement boards are considered water-resistant, it is incorrect to assume that they are completely waterproof. While making these boards, water is used to mix Portland cement with other additives. This means the cement in the board can still absorb some water. If left in water for a long period, the water can, with time, pass through to the other side. If the material on the other side of the cement board, or if it is attached to a wood frame, the frame would absorb water. Over time, this wooden frame would start to grow mold. Effectively, the structure deteriorates. Thus, these boards need to be reinforced with waterproof material.
2. Using Drywall Screws Instead of Cement Board Fasteners
While installing the cement boards, some installers may prefer drywall screws. This is because it is easier to drill through boards, shortening installation time. However, the screws should be used only when installing drywall. When these cement boards are installed in moisture-prone environments, the screws can corrode. This rust leaves stains on the surface. Further, as the screw corrodes, it weakens, risking the structural integrity of the installed boards. The screws heads are also thinner compared to normal fasteners for the cement board. If the boards are exposed to excess load, the thinner screw heads can experience pull-through failure, reducing holding power.