Mold on Wood Framing and Structural Lumber

Wood: A Semi-Porous Material

Unlike highly porous materials such as drywall and carpet, solid wood is classified as semi-porous. This distinction matters significantly for remediation decisions:

Why Wood Is Often Salvageable

Denser structure limits mold penetration
Surface contamination can usually be removed
Structural integrity often preserved if caught early
Replacement is expensive and disruptive
Proper cleaning restores the wood to acceptable condition

Types of Wood in Homes

Solid lumber (studs, joists, rafters)
Plywood (sheathing, subfloors)
OSB (oriented strand board)
Engineered lumber (LVL, I-joists)
Hardwood flooring
Trim and millwork

Solid lumber is most salvageable. Engineered products vary.

When Wood Can Be Cleaned

Wood can typically be cleaned and retained when the following conditions are met:

Mold growth is on the surface only (not deeply embedded)
The wood is structurally sound (not soft, rotted, or crumbling)
Moisture content has been reduced to acceptable levels (below 15-19%)
The moisture source has been identified and corrected
Growth can be removed by surface cleaning methods

Good Candidates for Cleaning

Wall studs with surface growth
Floor joists with light contamination
Roof rafters and trusses
Subflooring with surface mold
Hardwood floors (if structurally sound)

May Require Replacement

Wood that is soft or crumbling
Heavily saturated engineered products
OSB with significant mold penetration
Particleboard (highly porous)
Wood with structural damage from rot

When Replacement Is Needed

Wood must be replaced when:

Structural integrity is compromised (soft, rotted, or crumbling)
Wood rot (decay fungus) has developed in addition to mold
Moisture damage has caused warping or delamination
The wood cannot be dried to acceptable moisture levels
Mold has penetrated too deeply for surface cleaning to be effective
Engineered wood products have absorbed significant moisture

Wood Cleaning Techniques

Several methods are used to clean mold from wood surfaces, often in combination:

HEPA Vacuuming

Always the first step. HEPA vacuuming removes loose spores and debris before wet cleaning, preventing them from becoming airborne or being driven into the wood grain.

Sanding and Wire Brushing

For surface mold on unfinished wood (studs, joists, sheathing):

1

HEPA vacuum first

Remove loose contamination before mechanical cleaning.
2

Use appropriate tools

Wire brushes, sanding sponges, or power sanders depending on the surface.

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3 more steps in this process

Wet Cleaning

After mechanical cleaning, a damp wipe with detergent solution removes remaining surface contamination:

Use clean water with mild detergent
Wipe with damp (not wet) cloths
Work in sections, using fresh cloths frequently
Allow wood to dry completely after cleaning
Do not saturate wood with cleaning solution

Encapsulation Options

After cleaning, encapsulation may be appropriate in certain situations:

What Is Encapsulation?

Encapsulation involves applying a sealant over cleaned wood surfaces. This locks in any residual staining and provides a barrier against future moisture and mold growth.

Common encapsulants include antimicrobial sealers, shellac-based primers, and specialized mold encapsulation products.

When Encapsulation Is Appropriate

After thorough cleaning and drying
When staining remains after cleaning
In crawlspaces and attics (with proper ventilation)
As part of a comprehensive remediation plan
When recommended by a qualified professional

S520 Material Categories

The IICRC S520 standard categorizes materials by porosity, which determines remediation approach:

Porous (Category 3)

Usually Remove

Drywall
Insulation
Carpet and padding
Ceiling tiles
Particleboard

Semi-Porous (Category 2)

Often Cleanable

Solid lumber
Plywood
Hardwood flooring
Engineered wood (varies)
Concrete (sometimes)

Non-Porous (Category 1)

Usually Clean

Metal
Glass
Hard plastics
Sealed surfaces
Tile and glazed ceramics

Wood structural members (studs, joists, rafters) fall into Category 2, making them good candidates for cleaning when structurally sound. See our standards guide for more on IICRC S520.

Common Wood Mold Mistakes

Using bleach on wood (does not penetrate, leaves moisture)
Skipping HEPA vacuuming before sanding (spreads spores)
Sanding without containment or air filtration