# Is Cement Board Mold Resistant? The Ultimate Homeowner‘s Guide

- Canonical: https://33rdsquare.com/is-cement-board-mold-resistant/
- Published: 2023-10-30
- Author: Lillie Gabler
- Categories: [Tips](https://33rdsquare.com/category/home/tips/)

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As homeowners, we all want to protect our property from mold. Cement board is commonly used in bathrooms, kitchens and other damp areas of homes. But how mold resistant is cement board really? Does it require any special treatment to prevent mold growth? This comprehensive guide will examine cement board‘s natural mold-fighting properties and provide tips to keep it free of mold long-term.

## What Is Cement Board and Where Is It Used?

![](https://www.homestratosphere.com/wp-content/uploads/2020/11/types-of-cementboard-oct29.jpg)

Cement board, also known by brand names like Hardiebacker, Durock and Fiberock, is a durable, cement-based material often used as a moisture-resistant underlayment for tiling. It contains a core of concrete reinforced with fibers like fiberglass mesh.

As a backer board, cement board provides a sturdy foundation for tiles in:

- Bathrooms – walls and floors
- Kitchen backsplashes
- Showers and tub surrounds
- Steam rooms and saunas
- Laundry and utility rooms
- Balconies and porches

Cement board resists damage from water and humidity better than many alternatives. Its strength and mold resistance make cement board ideal for wet areas.

**Cement Board‘s Composition**

Cement board consists of:

- Sand + aggregate (limestone, clay)
- Portland cement
- Reinforcing fibers (fiberglass mesh)

This combination results in a water-resistant material able to withstand exposure to moisture. But all cement board is not created equal when it comes to mold prevention.

## Is Cement Board Naturally Mold Proof?

Cement board itself is mold, mildew and moisture resistant. Its dense concrete core leaves minimal space for mold to grow. And it contains no paper or organic materials that provide food for mold.

Lab tests of cement board samples found **no mold growth** after extended exposure to hot, humid environments. Research showed cement board has **exceptional** natural mold and moisture resistance compared to:

- Drywall
- Plywood
- Oriented Strand Board (OSB)
- Fiberboard

However, cement board should not be considered 100% impervious to mold. **Mold spores exist everywhere** in our homes. If they land on damp cement board, they can eventually proliferate into colonies. Tiny gaps or cracks in cement board can also allow moisture seepage and mold growth.

**No material is naturally mold proof**. But cement board‘s composition gives it a huge advantage against mold compared to other common building materials.

## Proper Installation = Max Mold Protection

To leverage cement board‘s natural mold resistance, correct installation is key. With good installation technique, we can **minimize moisture penetration** and opportunity for mold growth.

Here are pro tips for proper cement board installation in wet areas:

### Step 1: Prepare the Studs

- Mount cement board directly to studs, not drywall or plaster.
- Space wood studs no more than 16 inches on center for support.
- Use corrosion resistant screws like galvanized when affixing to metal studs.

### Step 2: Cut and Mount the Boards

- Leave a 1/8" – 3/16” gap between boards to allow for expansion.
- On walls, install vertically with seams staggered.
- Screw ever 8”-10” around the edges and every 12” in the field of the board.

### Step 3: Tape and Seal Seams

- Cover all seams and corners with fiberglass mesh tape.
- Use thinset mortar to embed the tape and create a continuous surface.
- Seal around fixtures, pipes, valves, etc. with 100% silicone caulk.

### Step 4: Waterproof Entire Surface

- Apply waterproofing membrane across ALL cement board surfaces.
- Use either liquid sealant or paint-on waterproofing made for cement board.
- Allow to fully cure per manufacturer instructions before tiling.

**Skipping waterproofing risks moisture intrusion and mold growth!** The waterproof coating seals the porous concrete and tiny gaps.

💡Pro Tip: Only use adhesives and membranes recommended for cement board. Some adhesives can react with cement and fail prematurely.

With good prep and diligent waterproofing, we‘ve created a durable moisture barrier that will keep mold at bay.

## How to Spot Mold Growth on Cement Board

Even properly installed cement board can develop mold if exposed to excessive moisture. Here‘s what to look for:

**Dark patches or spots** – Mold growth often starts off looking like dark spots or greenish, blackish, or brownish stains.

**Musty odor** – The fungi release a "moldy" smell as they grow. Even a faint whiff likely means mold is present.

**Soft or crumbly texture** – As mold takes hold, it can cause cement board to feel slightly spongy or brittle in the affected area.

**Flaking or peeling** – Bad mold damage may cause the cement board surface to flake away or peel.

**Moisture** – Excess dampness anywhere around the cement board can contribute to mold.

At the first sign of moisture or mold, take prompt action. Thorough cleaning and drying can remove early mold growth before major damage occurs.

## Mold Removal and Remediation

If caught early, minor mold on cement board can often be removed with thorough cleaning:

**Safety first!** Wear goggles, gloves, and an N95 respirator mask when working with mold.

1. Remove surface dirt and grime with a nylon brush or vacuum.
2. Mix 1 part bleach + 3 parts water and apply to moldy areas. Let sit 10-15 minutes.
3. Scrub with a stiff nylon brush and rinse cleaned area thoroughly.
4. Allow cement board to dry fully before resealing or tiling.
5. Consider applying a mold-resistant sealant after cleaning for added protection.

For more extensive mold damage:

- Consult a mold remediation pro for containment and safe removal.
- Cut away badly damaged sections of cement board and replace.
- Address underlying moisture issues before reinstallation.

With major mold growth, cement board replacement may be required to fully remediate the problem. Prevention is definitely key to avoid expensive removals!

## Maintaining Mold Resistance Long-Term

To keep cement board free of mold over time:

- Check for leaks, damage or loose tiles immediately. Make any needed repairs promptly.
- Routinely reapply waterproofing sealants as they wear over time.
- Address any moisture issues, like leaks or high humidity.
- Ensure adequate airflow and ventilation behind boards.
- Clean any mold ASAP before extensive growth.

With proper installation and vigilant maintenance, cement board can resist mold for decades. But we must stay on top of inspecting for problems and re-sealing as needed. A little prevention goes a long way!

👉Pro Tip: Higher quality cement board brands like James Hardie HardieBacker score better on mold resistance testing. Opt for premium cement board when possible.

## How Cement Board Compares to Other Backer Boards

Let‘s examine how cement board stacks up against a few other common tile backer board materials.

| Material | Mold Resistance | Cost | Uses |
| --- | --- | --- | --- |
| Cement Board | Excellent | Moderate | Wet rooms, shower walls, high humidity areas |
| Drywall | Poor | Low | Occasional tile backsplash |
| Plywood | Low-Moderate | Low | Budget tile jobs |
| Tileboard | Very Good | High | Shower walls, high-end installs |
| Fiberboard | Very Poor | Low | Avoid in damp locations |

**The takeaway:** Cement board provides the best balance of mold resistance and moderate cost. It‘s the ideal choice for tiling wet, humid areas of a home.

Tileboard also scores well for mold resistance, but the higher price point makes it less than ideal for larger jobs. We want mold protection that fits in our budget!

## Conclusion: Leveraging Cement Board‘s Mold-Fighting Properties

When properly selected, installed, and maintained:

✅ Cement board resists mold growth thanks to its durable concrete composition.

✅ It provides superior moisture protection compared to materials like drywall and plywood.

✅ Correct waterproofing and sealing maximize cement board‘s inherent mold resistance.

While no material is 100% mold proof, diligent homeowners can leverage the mold-fighting properties of cement board. Follow the recommendations in this guide to get the most out of cement board for all your bathroom, kitchen, and wet room projects. We‘ll keep mold safely at bay while enjoying durable and attractive tiled finishes!

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Source: [Is Cement Board Mold Resistant? The Ultimate Homeowner‘s Guide](https://33rdsquare.com/is-cement-board-mold-resistant/)