Mold Remediation Steps for Contractors and Property Managers

Mould remediation is one of the most regulated cleaning operations in the trades. The IICRC S520 standard sets the procedural baseline that property managers, contractors and insurance adjusters expect. Following it protects occupants, workers and the contractor's liability exposure. Here is the step by step process.

Step 1: Inspection and Documentation

Before any equipment is set up, document the affected area. Photograph all visible mould growth, take moisture readings with a moisture meter and use a thermal imager to find hidden moisture. Map the contamination zones into Conditions 1 (normal), 2 (settled spores) and 3 (active growth) per IICRC S520.

Step 2: Containment

Seal off the work area from clean areas using 6 mil polyethylene sheeting. For Conditions 2 and 3, build full containment with a critical barrier (taped poly walls). Use mobile containment systems for ICRA Class 4 work or any project requiring three stage decontamination.

Step 3: Negative Air

Set up a HEPA HEPA air scrubber exhausting outside the contained area. This creates negative pressure (typically 5 Pa or 0.02 inches of water column below ambient). Air can only enter the work area through controlled paths and can only leave through the HEPA filter.

Step 4: PPE for Workers

• N95 respirator minimum (P100 for heavy growth)
• Disposable Tyvek suit
• Nitrile gloves
• Eye protection (sealed goggles)
• Boot covers

Step 5: Source Removal

Remove all materials with active mould growth. Drywall, carpet, insulation, ceiling tile. Bag the debris in 6 mil contractor bags, double bag, seal with tape and remove via the decontamination route.

Step 6: HEPA Vacuum

HEPA vacuum every surface in the contained area. Wipe hard surfaces with a detergent solution. Repeat the vacuum and wipe cycle until visibly clean.

Step 7: Address the Moisture Source

Mould only grows where there is moisture. Repair the leaking pipe, the roof, the foundation drain or whatever is feeding the moisture. If the source is not addressed, the mould comes back.

Step 8: Dry the Area

Dry the affected materials below 60 percent relative humidity. Use a commercial dehumidifier sized to the room. LGR dehumidifiers are the standard for mould drying because they pull moisture from surfaces and air at lower humidity levels than standard refrigerant units. Keep moisture meters on the framing and substrate during drying.

Step 9: Encapsulate If Needed

For Conditions 3 areas where some material had to be left in place, apply an antimicrobial encapsulant. This is not a substitute for source removal; it is a final layer of protection on remaining wood framing.

Step 10: Post Remediation Verification (PRV)

An independent indoor air quality (IAQ) consultant takes air and surface samples. Acceptance criteria vary by jurisdiction but typically require post remediation spore counts below outdoor or unaffected indoor levels. The clearance test is what makes the job complete.

Step 11: Reconstruction

Once cleared, reconstruction proceeds. Drywall, paint, flooring, trim. The remediation contractor and the rebuild contractor are often different parties.

Common Pitfalls

• Skipping containment on small jobs (spores migrate everywhere)
• Not addressing the moisture source (mould returns)
• Stopping at visible mould (hidden growth in cavities is missed)
• Reusing porous materials (carpet, drywall, insulation)
• Skipping the clearance test

Mould remediation done correctly costs more in equipment and labour than it appears at first glance. But the alternative, a second remediation a year later because the source was not addressed, is twice as expensive and twice as disruptive. Follow the standard, document the process, and the job stays out of court.