Case Study: Rental property mold kept returning despite DIY treatments
A Nashville landlord noticed something concerning during a routine inspection of his rental property. Black-gray spots were appearing in two locations: on a pocket door inside the bathroom, and between the storm door and exterior door at the entrance.
With tenants still living in the home, he wanted to address the issue quickly and discreetly. He tried over-the-counter mold and mildew killers first, hoping for a simple fix. The spots disappeared initially—but within weeks, they came back.
When Claro inspected the property, the pattern became clear. Surface cleaning wasn't addressing the root problem—mold spores were embedded in the porous materials and moisture was still present in both locations.
Air quality testing revealed shocking contamination levels. The bathroom showed a total spore count of 26,000 per cubic meter—dominated by Penicillium/Aspergillus at 26,000 spores. Even the bedroom, far from the visible problem areas, registered 2,400 spores with Penicillium/Aspergillus at 2,000.
The pocket door issue pointed to bathroom humidity that wasn't being properly ventilated. The storm door problem indicated trapped moisture between the two doors—likely from condensation that couldn't dry out. But the real concern was that these visible spots were just the tip of the iceberg. The tenants had been breathing contaminated air throughout the entire rental property, and the landlord faced serious liability issues if the problem wasn't properly resolved.
Claro performed a whole-home dry fog treatment to address both the visible mold and the extensive airborne contamination throughout the property. The EPA-certified process reached into the pocket door cavity, the space between the exterior and storm doors, and every other area where spores had traveled.
Post-treatment testing confirmed complete remediation: total culturable fungi dropped to less than 13 CFU/m³—essentially undetectable. The bathroom's catastrophic 26,000 spores were completely eliminated. The bedroom returned to safe levels. The black-gray spots were gone, and more importantly, they didn't come back.
The landlord was able to address the moisture sources—improving bathroom ventilation and adjusting the storm door to allow better airflow—knowing the mold contamination had been properly eliminated. The tenants remained in place throughout the treatment with minimal disruption.
This case demonstrates why DIY surface treatments often fail with rental properties: they kill visible mold but don't address the extensive contamination that spreads through the entire home. What looked like two small problem spots had created 26,000 spores in the bathroom alone—a serious health hazard and liability risk.
