What Is Containment?

Containment is one of the most critical steps in professional mold remediation and one of the most commonly skipped in DIY attempts. When mold colonies are disturbed — by cutting, scrubbing, or removing contaminated material — they release enormous quantities of spores into the air. Without containment, these spores migrate throughout the building via air currents and HVAC systems, potentially seeding new growth in previously unaffected areas.

Professional containment uses 6-mil polyethylene sheeting to create a physical barrier between the work zone and the rest of the building. Seams are taped airtight, doorways are sealed, and HVAC vents in the work area are covered. The goal is to create an isolated enclosure where spore release during work cannot escape into the broader living space.

Critical to effective containment is negative air pressure, maintained by an air scrubber or negative air machine exhausted to the outside. By running the fan constantly during work, the containment zone is kept at slightly lower air pressure than adjacent areas — meaning airflow is always inward, never outward. Any breach in the containment will pull clean air in rather than pushing contaminated air out.

The scale of containment depends on the size of the affected area. Small isolated patches (under 10 square feet) may not require full negative pressure containment. Medium areas (10–100 sq ft) typically require basic containment. Large areas (over 100 sq ft) require full containment with negative pressure, double entry airlocks, and worker decontamination procedures. These thresholds come from the IICRC S520 standard.