Mold Behind Drywall — South Weber, UT

Loss Type: Mold Remediation / Hidden Wall Cavity Mold from Prior Water Intrusion
Location: South Weber, UT near Cottonwood Lane
Response Time: Next-day scheduled
Job Duration: 3 days
Insurance: No – homeowner self-pay

The Situation

A homeowner near Cottonwood Lane in South Weber contacted us after a remodeling contractor discovered significant mold growth inside a bathroom wall during a planned renovation. The contractor had removed drywall in the master bathroom to rough in a new shower and found black mold colonizing the wall cavity framing on the exterior wall — growth the homeowner had no prior knowledge of. The renovation was paused and the contractor recommended professional remediation before any new work could proceed.

We were on-site the following morning to assess the scope.

The Problem

Inspection of the exposed wall cavity revealed mold growth on the stud faces, the bottom plate, and the OSB exterior sheathing behind the shower wall across an area of approximately 35 square feet. A moisture meter reading on the OSB sheathing showed it was still at elevated moisture content despite no active leak being present — indicating the original water intrusion source had stopped at some point in the past but the wall cavity had never fully dried, allowing the mold to persist and spread in the residual moisture.

Investigation identified the likely historical source — a window above the shower that had a failed seal at the sill flashing. The sill flashing had since been replaced during a window replacement project approximately 18 months prior, which had stopped the water intrusion, but the wall cavity had remained sealed and damp ever since with no opportunity to dry out. This is a common pattern we see with hidden water intrusion — the source gets fixed but the wall cavity never dries. The mold had continued to develop in the residual moisture even after the source was corrected.

Because the renovation contractor had already opened the wall cavity there was no additional demolition required for the remediation — the full affected area was already accessible.

What We Did

We established containment of the bathroom using 6-mil poly sheeting sealed at the doorway and ran a HEPA air scrubber throughout the remediation to capture airborne spores. Per IICRC S520 mold remediation standards the scope included:

• Wire brushing of all mold-affected stud faces, bottom plate surfaces, and OSB sheathing
• HEPA vacuuming of all disturbed surfaces and surrounding framing
• Application of EPA-registered antimicrobial to all affected surfaces with required dwell time
• Application of EPA-registered encapsulant to all treated surfaces after drying
• Structural drying of the OSB sheathing using air movers and a dehumidifier until readings reached target before encapsulation
• Post-remediation air sampling by an independent industrial hygienist

Because the OSB sheathing was still holding elevated moisture we ran a 24-hour drying cycle on the open cavity before applying the encapsulant — encapsulating over damp wood would have trapped moisture and prevented the treatment from being effective.

The Outcome

Post-remediation clearance testing confirmed spore counts within acceptable baseline levels. Once clearance was confirmed, structural framing was ready for drywall repair and the new shower installation. The renovation contractor resumed work the following week and completed the new shower installation with a properly sealed window sill and new waterproof membrane behind the shower surround. We provided the homeowner with a written remediation report and clearance certificate for their records — documentation that also confirmed the scope and completion of the work for the contractor’s files.

“My contractor found a wall full of mold and had to stop work. Upkeep came out the next day, explained exactly what had caused it and how long it had likely been there, remediated it properly, and had it tested and cleared within three days. My renovation got back on track quickly. Thorough and professional.”

— R. Ashby, South Weber, UT

We’ve also handled another South Weber project involving category 3 sewage loss in a similar residential setting. Browse our full library of case studies to see how we’ve handled mold, water damage, and sewage events across Davis County.