Microbial Growth Day 6 Cover vs Disclose Decision Tree

Why this matters

Visible microbial growth that appears during the drying phase of a water loss is the single highest-stakes finding a restoration tech encounters. Continuing to dry without disclosing is a documented path to litigation; over-disclosing without confirming amplification can blow scope unnecessarily and damage the customer relationship. The decision is technical (is this true amplification or surface mildew that wipes off) and ethical (what does S500 and S520 require us to communicate). This article walks the cover-vs-disclose decision on a Day 6 finding, where the loss was tracking to convergence but the chamber surfaced a growth spot.

Symptom presentation

Day 6 walkthrough on a Cat 1 loss in a finished basement. Drying has been progressing. Chamber psychrometrics have been within S500 parameters. Pin reads have dropped from 22 percent to 13 percent on the wettest wall. While doing a final bracket, the tech spots a 4-inch by 6-inch dark stain on the back of the baseboard, with surface fuzz. The stain was not there on Day 4 photos.

Alternative presentation: Day 6 finds discoloration on the drywall paper at a point that has been wet throughout the dry. Pin reads at the discoloration are still elevated (14 percent) while surrounding area is at dry standard (10 percent).

Alternative presentation: Day 6 customer-reported odor. Tech smells a musty note in a corner the equipment has not been targeting. Pin reads at the corner are 16 percent; thermal imaging shows a cold area in the wall cavity that was not flagged on Day 1.

Quick checks

Identify the growth visually. True microbial amplification looks fuzzy, often colored (black, green, white, pink), and is structurally attached to the substrate. Surface mildew is usually a thin film that wipes off, often follows a moisture pattern, and is not three-dimensional.

Wipe test. With gloved hand and a moist cloth, gently wipe the growth area. Mildew on a non-porous surface wipes off without residue and the substrate underneath is unaffected. True amplification on a porous substrate leaves staining and may regrow within hours of the wipe.

Confirm wetness at the growth area. Pin meter at the growth point. Amplification requires moisture; if the area reads dry, the growth either pre-dates this loss or has another moisture source.

Isolation tree

Branch A: small surface mildew (less than 10 square feet, wipes off, non-porous substrate, pin reads at dry standard). Surface clean and continue. Document with photos and a clean log; no scope change required. This is typical bathroom or kitchen baseline mildew not caused by the current loss.

Branch B: small amplification (less than 10 square feet, porous substrate, growth attached, pin reads still elevated). S520 Condition 2 limited area. Disclose, isolate, and remediate. Set containment, HEPA-filtered negative pressure, remove the affected porous material, apply EPA-registered antimicrobial per S520 protocols, then continue drying.

Branch C: moderate amplification (10 to 100 square feet OR multiple isolated areas). S520 Condition 2 or 3 depending on area. Disclose to homeowner and adjuster in writing. Stop drying-only scope; transition to remediation scope. Engage third-party assessor if jurisdiction requires (multiple states require third-party in some scenarios, see state references in restoration library).

Branch D: large amplification (greater than 100 square feet OR cavity-extensive). S520 Condition 3. Mandatory disclosure. Third-party assessor strongly recommended. Full remediation protocol with containment, PPE, removal, decontamination, post-remediation verification before any drying continues.

Branch E: customer pre-existing growth. Growth pattern that is clearly older than the current loss (dry, dusty, no associated moisture from this event). Document as pre-existing in the file; disclose to customer that pre-existing growth was observed; note that current loss has not amplified it; recommend separate remediation.

Confirming diagnosis

Photograph the growth at scale. Tape measure or ruler in frame, with timestamp and location. The Day 6 finding photograph is the single most important documentation in any potential dispute.

Photograph the Day 4 reference (or any prior date that did not show the growth). The temporal documentation establishes that the growth was not present at intake and developed during the drying period.

Confirm moisture content at the growth area. The amplification narrative depends on moisture being present; if the area reads dry, the cause analysis changes.

Document the chamber conditions. Even when chamber psychrometrics were within S500 parameters, a microbial bloom occurred. This is not a contractor failure if the chamber was managed properly; documentation protects both the customer and the contractor.

Remediation

Branch A path: clean, continue, document. The finding goes in the file but does not change scope.

Branch B path: disclose verbally and in writing to customer the same day. Disclose to adjuster within 24 hours. Set localized containment. Remove the porous material with EPA-registered antimicrobial decontamination of adjacent areas. Document the remediation steps in a supplemental scope.

Branch C, D path: stop drying-only scope. Issue a scope change order with the microbial finding documented. Engage third-party assessor if jurisdiction requires or if the customer wants independent verification. Containment, PPE, removal, decontamination, post-remediation verification per S520. Drying may continue in parallel or after, depending on the remediation containment overlap.

Branch E path: document as pre-existing, disclose to customer, recommend separate scope. Do not attempt to include pre-existing remediation in the current water loss claim without explicit adjuster approval; the resulting denial would damage the contractor's standing.

References

1. ANSI/IICRC S520-2024 Standard for Professional Mold Remediation, Conditions 1, 2, and 3 definitions.
2. ANSI/IICRC S500-2021 Standard for Professional Water Damage Restoration, Section 12.2.2 (Microbial Amplification).
3. EPA Document 402-K-01-001, Mold Remediation in Schools and Commercial Buildings, growth identification criteria.
4. ASTM D7338-21 Standard Guide for Assessment of Fungal Growth in Buildings.
5. NYC DOH Guidelines on Assessment and Remediation of Fungi in Indoor Environments, current edition.