Houston Homes: Cement Board Hiding Summer Mold?

By Franklin Everett Shaw

January 4, 2026

The musty smell hits you first, a subtle but persistent odor that clings to the air. You might dismiss it as just “old house smell,” but in Houston, that smell could be a warning sign. It’s a sign that mold, a silent invader, might be lurking behind your cement board siding, feasting on the moisture trapped within. Ignoring it could lead to serious health problems and costly repairs.

Houston’s humid subtropical climate is a breeding ground for mold. The combination of high temperatures and frequent rainfall creates the perfect environment for mold spores to thrive, especially behind porous materials like cement board siding if it’s not properly installed or maintained.

Cement board, while durable and resistant to many elements, isn’t waterproof. It’s water resistant. This means that if water penetrates the siding – through cracks, faulty flashing around windows and doors, or even just prolonged exposure to driving rain – it can become trapped behind the cement board, creating a damp, dark haven for mold.

So, how do you, the average Houston homeowner, determine if you have a mold problem lurking behind your cement board? Let’s dive into a step-by-step guide, focusing on the specific challenges and solutions relevant to our unique Gulf Coast environment.

First, visual inspection is key. Don’t just glance at your siding; get up close and personal. Look for these telltale signs:

Discoloration: Staining or discoloration on the cement board itself, particularly near seams, corners, or areas where the siding meets the foundation. This could appear as green, black, brown, or even white patches.
Cracks and Damage: Carefully inspect for cracks, chips, or other damage to the cement board. These openings provide easy access for water to penetrate. Pay special attention to areas around windows, doors, and where pipes or wires enter the house.
Bulging or Warping: If the cement board is bulging or warping, it could indicate significant moisture buildup behind the siding. This is a serious sign and warrants immediate investigation.
Caulk Condition: Check the caulk around windows, doors, and seams. Cracked, peeling, or missing caulk is a major entry point for water.

Next, the sniff test. As mentioned earlier, a musty or earthy odor is a strong indicator of mold. Sniff around the exterior walls, especially near the ground and around windows and doors. If you detect a suspicious odor, it’s time to investigate further.

Now, for the slightly more involved part: probing for moisture. This requires a bit of caution and some basic tools.

Gather your supplies: You’ll need a screwdriver (preferably a flathead), a moisture meter (available at most hardware stores), and a flashlight.
Choose your test areas: Focus on areas where you’ve noticed discoloration, cracks, or other signs of potential water damage. Also, target areas that are prone to moisture, such as near the foundation, under eaves, and around plumbing penetrations.
Probe gently: Using the screwdriver, gently probe the cement board in the selected areas. If the cement board feels soft or crumbly, it’s likely waterlogged and may be harboring mold.
Use the moisture meter: Insert the moisture meter probes into the cement board. A reading above 20% generally indicates excessive moisture and a potential mold problem.

Important Safety Note: When probing, be extremely careful not to damage any underlying wiring or plumbing. If you’re unsure about what’s behind the siding, it’s best to consult a professional.

If your visual inspection, sniff test, and probing reveal signs of potential mold, it’s time to call in the professionals. A qualified mold inspector can conduct a thorough assessment of your home, including air sampling and surface testing, to determine the extent of the mold problem and identify the specific species present.

In Houston, common mold species include Stachybotrys chartarum (black mold), Aspergillus, and Penicillium. Knowing the specific type of mold is crucial for developing an effective remediation plan.

Professional Testing Resources in Houston:

AAA Environmental: Offers comprehensive mold testing and inspection services throughout the Houston area.
Mold Inspection Sciences: Provides certified mold inspectors and detailed reports.
SanAir Technologies Laboratory: A reputable lab that analyzes mold samples collected by inspectors.

Remediation Strategies Specific to Cement Board:

If mold is found behind your cement board siding, remediation is essential. The process typically involves:

Containment: Sealing off the affected area to prevent the spread of mold spores to other parts of the house.
Removal: Carefully removing the affected cement board siding. This should be done by professionals wearing protective gear to avoid inhaling mold spores.
Cleaning and Disinfection: Cleaning and disinfecting the underlying surfaces to kill any remaining mold spores.
Repair and Replacement: Repairing any water damage and replacing the removed cement board with new siding.
Moisture Control: Addressing the underlying cause of the moisture problem to prevent future mold growth. This may involve repairing leaks, improving ventilation, or installing a vapor barrier.

Common Mistakes and Pitfalls:

DIY Remediation: Attempting to remove mold yourself without proper training and equipment can be dangerous and ineffective. Mold spores can easily spread, making the problem worse.
Ignoring the Source of Moisture: Simply removing the mold without addressing the underlying moisture problem is a temporary fix. The mold will likely return.
Using Bleach: While bleach can kill surface mold, it doesn’t penetrate porous materials like wood. It can also damage cement board and create a breeding ground for mold in the long run.
Improper Installation: Cement board siding must be installed correctly to prevent water intrusion. This includes proper flashing, sealing, and spacing.

Preventative Measures for Houston Homes:

Prevention is always better than cure. Here are some steps you can take to minimize the risk of mold growth behind your cement board siding:

Regular Inspections: Inspect your siding regularly for cracks, damage, and signs of moisture.
Proper Maintenance: Keep your gutters clean and free of debris to ensure proper drainage. Trim back any vegetation that is touching the siding.
Seal Cracks and Gaps: Seal any cracks or gaps in the siding with caulk or sealant.
Improve Ventilation: Ensure adequate ventilation in your attic and crawl space to reduce moisture buildup.
Consider a Vapor Barrier: If you live in a high-humidity area, consider installing a vapor barrier behind the siding to prevent moisture from penetrating the walls.
Professional Installation: When installing or replacing cement board siding, hire a qualified contractor who is experienced in working with this material and understands the specific challenges of the Houston climate.

Houston Building Codes and Mold:

While Houston doesn’t have specific mold remediation codes, it’s essential to follow best practices and industry standards when dealing with mold problems. The Texas Department of State Health Services (DSHS) regulates mold assessment and remediation services. Ensure that any mold inspector or remediator you hire is licensed by the DSHS.

Real-World Scenario:

Consider a homeowner in the Heights neighborhood of Houston. They noticed a musty smell in their living room and discoloration on the exterior wall. Upon closer inspection, they found cracks in the caulk around a window and signs of water damage on the cement board siding. They called a professional mold inspector who confirmed the presence of Aspergillus mold behind the siding. The remediation process involved removing the affected siding, cleaning and disinfecting the wall cavity, repairing the window flashing, and replacing the siding with new cement board. The homeowner also installed a dehumidifier in their living room to help control moisture levels.

By taking proactive steps to inspect, maintain, and protect your cement board siding, you can minimize the risk of mold growth and maintain a healthy indoor environment for your family. Don’t let mold take root in your Houston home. Stay vigilant, stay informed, and take action when necessary. Your health and your home are worth it.