Fiber cement boards are widely used in exterior and interior construction projects for their strength, water resistance, and durability. While most people associate them with wall cladding or façade systems, fiber cement boards are increasingly considered for use as underlayment in flooring systems—particularly under ceramic tiles or stone.
But is this material truly suited for flooring underlayment? And what should builders, architects, and installers consider before using it in this way?
In this article, we’ll take a closer look at the advantages and drawbacks of using fiber cement boards as flooring underlayment and explain when and where it is appropriate.
What Is Flooring Underlayment?
Flooring underlayment refers to the intermediate layer between the structural subfloor (usually concrete or plywood) and the finished floor surface, such as ceramic tile, vinyl, or hardwood. The purpose of this layer is to:
- Provide a smooth, stable, and level surface
- Improve moisture resistance
- Reduce deflection and joint movement
- Offer sound insulation or cushioning, depending on the material
The choice of underlayment can significantly affect the performance and durability of the entire floor system.
Why Use Fiber Cement Boards for Underlayment?
Fiber cement boards are made from a mixture of cement, sand, and cellulose fibers, resulting in a product that combines the strength of cement with the flexibility and dimensional stability of fiber. This makes them particularly suitable for wet or high-traffic areas.
Here are some of the key benefits of using fiber cement boards as flooring underlayment:
- Excellent Moisture Resistance
One of the standout features of fiber cement boards is their non-swelling, moisture-resistant nature. Unlike plywood, OSB, or gypsum boards, fiber cement does not warp, rot, or soften when exposed to water or humidity. This makes it ideal for applications in:
- Bathrooms
- Kitchens
- Laundry rooms
- Entryways
- Commercial wet zones
Even when used over a concrete subfloor that might have slight moisture migration, fiber cement remains dimensionally stable and safe to use.
- Strong and Rigid Surface
Fiber cement provides a rigid and stable surface, essential for tile and stone installations. A solid substrate minimizes the risk of:
- Cracked tiles
- Loose grout joints
- Deflection under heavy loads
Installers working with large-format tiles especially appreciate the extra stability fiber cement boards offer.
- Fire-Resistant Properties
As a non-combustible material, fiber cement boards offer improved fire safety over wood-based underlayments. This makes them especially appealing in multi-storey residential buildings, public areas, or commercial interiors where fire resistance is a code requirement.
- Termite and Mold Resistance
Because fiber cement boards are made from inorganic materials, they do not support mold or mildew growth and are not attractive to insects or pests. This is a major benefit in tropical climates, basements, or areas with poor ventilation.
- Long-Term Dimensional Stability
When installed correctly, fiber cement boards do not expand or contract significantly with temperature or humidity changes. This ensures that tiles, adhesives, and grout remain intact over the long term.
Limitations to Consider
While fiber cement boards bring several advantages to flooring systems, they are not without drawbacks. It’s important to weigh these limitations before selecting them for your project.
- Heavier Than Other Underlayment Materials
Fiber cement boards are relatively heavy compared to alternatives like foam, cork, or gypsum. A standard 6 mm (¼ inch) sheet can weigh over 12 kg. This may pose challenges during transportation, handling, or installation—especially on upper floors or large-scale jobs.
- Requires Proper Fastening
Improper fastening can lead to movement, noise, or cracks in the finished surface. Fiber cement boards must be:
- Installed over a clean, level subfloor
- Secured using corrosion-resistant screws (not nails)
- Joints staggered and filled properly
- Gaps between boards left to allow minimal movement (per manufacturer instructions)
Skipping these steps often results in premature failure, especially in areas with temperature fluctuations or under heavy foot traffic.
- Not Ideal for All Types of Flooring
Fiber cement boards work best under tile, natural stone, and mortar-set finishes. They are not ideal for floating floors like engineered wood, laminate, or vinyl planks unless specifically recommended by the flooring manufacturer. For those systems, a foam or cork underlayment may offer better performance and sound insulation.
When to Use Fiber Cement Boards as Underlayment
Fiber cement boards are highly suitable for:
- Bathroom and wet room floor bases
- Commercial kitchens and restaurant flooring
- Entryways exposed to weather and foot traffic
- Underfloor heating systems (when approved by manufacturer)
- Any flooring system that requires a rigid, water-resistant substrate
Avoid using them where weight is a critical issue, or where floating floors require flexible underlay.
Final Thoughts
Fiber cement boards can be an excellent underlayment choice in many construction and renovation scenarios—particularly where water exposure, fire risk, or surface rigidity are concerns. However, like any building material, they must be installed properly to perform effectively over time.
If your flooring system involves tiles, stone, or cementitious toppings, and especially if you’re working in moisture-prone areas, fiber cement boards are well worth considering as a long-lasting underlayment solution.
👉 Visit the Smartfiber Fiber Cement Board page to explore specs, sizes, and delivery options.
Authored by Smartcon Int’l. Trade & Marketing Ltd. on 03.08.2025. All rights reserved.