Evaporation Rate Stalled Day 3 Decision Tree

Why this matters

Day 3 is when chamber data tells the truth. A loss that was set up correctly on day 1 should show daily declines in moisture content and a measurable drop in chamber GPP. When day 3 readings sit flat against day 2, something is overriding the chamber. The fix is rarely "more equipment" - that is the default reflex but it is the most expensive wrong answer. The fix is to find what is feeding moisture back into the chamber and close it. Equipment days that pile up past day 5 on a standard residential loss are almost always chamber-leakage problems, not equipment-capacity problems.

Symptom presentation

You walk in for the day-3 equipment day. The pin-meter readings on framing have not moved since yesterday. The chamber GPP is the same as yesterday. The LGRs are running but the condensate pump output has dropped to a trickle. The picture across the four failure modes:

• Source still open: moisture content is climbing in one mapped zone while declining elsewhere.
• Chamber leakage: GPP is flat or climbing despite running equipment.
• Cavity isolation: surface readings dry, cavity readings still wet.
• Substrate at equilibrium: readings flat at the dry-standard reference, but documentation says "still wet."

The fix path is different for each.

Quick checks before adding equipment

• Re-walk the moisture map. Compare day 1, day 2, day 3 readings at the same probe points. If one zone is climbing while others fall, the climbing zone is the failure.
• Re-confirm dry standard. The reference area MC may have drifted up from a humid HVAC supply or window left open.
• Read the equipment. LGR water removal that was 8 gallons/day on day 1 and is 2 gallons/day on day 3 is normal if the chamber is winning. If readings are flat but LGR output is high, water is entering the chamber from somewhere.
• Check the seal. Containment poly intact, doors closed, HVAC supplies covered or chamber-isolated.

Isolation tree

Step 1: open source.

• Re-inspect the source-control work from day 1. Plumbing repair holding? Tarp still tight? Drain repair in place?
• Probe the highest reading on the climbing zone with a moisture meter at multiple depths. A wet upper plate while the lower wall is drying indicates water entering from above (roof, attic, second-floor plumbing).
• If the source is still open, drying does not resume until it is closed. Equipment continues to run at significant cost without progress.

Step 2: chamber leakage.

• Check containment. 6-mil poly walls intact at the demo zone perimeter; tape seals not pulling away; floor sweeps in place at the bottom of poly walls.
• Check HVAC. If the home HVAC is delivering 80 GPP outside air to the chamber, the LGR is running against the supply. Either shut HVAC off (with tenant agreement), or seal the chamber with poly walls and run the chamber isolated.
• Check exhaust. If the chamber has a window or door cracked for "air circulation" by the homeowner, the chamber is exchanging with outside air. Close it and document.
• Check the door. Equipment day traffic in and out at 5+ entries per day exchanges chamber air. Limit access to one entry per day for inspection.

Step 3: cavity isolation.

• Surface MC at the dry standard, cavity MC at 18%+ still: cavity airflow is the bottleneck.
• Solution: directed air movement into cavities. Inject ports through baseboard cutouts, register-feeds at HVAC supplies into wall cavities, snake hose into accessible cavities through small drilled holes.
• Without cavity airflow, surface drying creates a false "almost done" reading while wet cavities continue to feed vapor back through the dry surface.

Step 4: substrate at equilibrium.

• Affected area MC is matching dry-standard MC within 2%.
• GPP is at or below target (under 60 for Class 2, under 50 for Class 3).
• Water removal from equipment is near zero.
• Decision: validate per S500 Section 13 with 24-hour hold, demobilize. The chamber has won; running another day adds cost without benefit.

Confirming diagnosis

Three measurements before any equipment change:

• Map the moisture content of every wet material on day 3 against day 1 and day 2. The trend line tells you the story; a single day's flat reading can be normal drying-curve plateau, two days flat is the call to investigate.
• Measure chamber GPP versus outside GPP. Chamber should be lower than outside by at least 10 GPP if it is winning. Chamber matching or exceeding outside means leakage.
• Probe at least three previously-unmeasured points (under floor structure, behind cabinets, in suspect cavities). Hidden wet substrate will not move the visible readings.

The diagnosis is not "add more equipment." The diagnosis is "what is the chamber fighting that it shouldn't be."

Remediation by failure mode

Open source:

• Re-secure the source. Plumbing tighten, tarp re-set, drain plug.
• Resume drying. Day 3 becomes the new day 1 for the chamber under the corrected condition.

Chamber leakage:

• Seal the leak path (HVAC isolation, additional poly containment, door discipline).
• Confirm GPP drops within 4 to 6 hours after seal.
• Resume normal timeline.

Cavity isolation:

• Add cavity airflow via inject ports, register-feeds, or snake hose.
• Do not add open-chamber air movers; the chamber surface is already in equilibrium.
• Re-check cavity MC at 12-hour interval to confirm drying resumed.

Substrate at equilibrium:

• Hold 24 hours under operating equipment.
• Validate readings at the dry standard plus or minus 2% MC, document per S500 Section 13.
• Demobilize.

References

• IICRC S500 Standard for Professional Water Damage Restoration, Section 13 (drying goals), Section 14 (validation), 2021 edition
• IICRC Applied Structural Drying course manual, chapter on drying curves and chamber control
• ASTM E96, Standard Test Methods for Water Vapor Transmission of Materials (substrate vapor pressure principles)
• Dri-Eaz Engineering Bulletin on chamber GPP and equipment sizing
• Phoenix R175 desiccant operating curve, vapor pressure differential at low temperatures