Why Does Mould Grow on Wood?

Wood is one of mould's favourite surfaces. It's porous, often retains moisture, and provides an organic food source that mould spores thrive on. Whether it's timber framing, floorboards, decking, furniture, or skirting boards, any wooden surface exposed to humidity, condensation, or water ingress is at risk.

Mould typically begins to colonise wood within 24–48 hours of moisture exposure. The key conditions that accelerate growth include:

• Humidity above 60% — common in bathrooms, laundries, and poorly ventilated rooms
• Water leaks or flooding — even minor leaks behind walls can saturate timber
• Condensation — particularly on timber window frames and sills
• Poor airflow — enclosed spaces like under-floor cavities and inside wardrobes

How to Identify Mould on Wood

Mould on wood can appear in several forms depending on the species and how long it's been growing:

• Black or dark green patches — often Cladosporium or black mould (Stachybotrys chartarum)
• White fuzzy growth — commonly early-stage mould or efflorescence on painted timber
• Grey or blue-green staining — often sapstain fungi, which penetrate deep into the wood grain
• Musty odour — a reliable indicator even when mould isn't yet visible

If the mould has penetrated the wood grain and cannot be wiped away, it has likely taken hold below the surface — requiring a stronger treatment approach.

Health Risks of Mould on Wood

Mould on wood isn't just an aesthetic problem. Airborne mould spores released from colonised timber can cause a range of health issues, particularly for those with respiratory conditions, allergies, or compromised immune systems:

• Respiratory irritation, coughing, and wheezing
• Skin and eye irritation
• Aggravated asthma and hay fever symptoms
• Headaches and fatigue in heavily contaminated environments

Black mould (Stachybotrys) in particular produces mycotoxins that can be harmful with prolonged exposure. If you suspect significant black mould growth in your home, it's worth acting quickly.

How to Remove Mould from Wood

The approach to mould removal depends on how deeply the mould has penetrated the wood and the size of the affected area.

Step 1: Protect Yourself

Before you start, put on gloves, a P2 respirator mask, and eye protection. Open windows to ventilate the space and reduce spore inhalation.

Step 2: Apply a Mould Remover

Spray the affected area with a quality mould remover — one specifically formulated to kill mould at the root, not just bleach the surface. Surface bleaching without killing the spores means mould will return within weeks.

Green Goo's Heavy Duty Anti Mould Spray is designed to penetrate porous surfaces like wood, killing mould spores at the source while being safe for use around your family and pets. Simply spray, leave to dwell for a few minutes, then wipe away.

Step 3: Scrub if Needed

For stubborn or deep-set mould, use a stiff-bristled brush to work the product into the grain. Avoid using excessive water, which can further saturate the timber.

Step 4: Dry Thoroughly

After treatment, ensure the wood dries completely. Use fans, a dehumidifier, or open windows to accelerate drying. Mould will return if moisture remains.

When to Replace Rather Than Treat

If mould has deeply penetrated structural timber — particularly load-bearing framing or flooring joists — surface treatment may not be sufficient. Signs that timber may need replacing include:

• Soft, spongy, or crumbling wood (indicating rot alongside mould)
• Mould that returns repeatedly despite treatment
• Structural timber with visible deep staining throughout the grain

In these cases, consult a licensed builder or remediation specialist.

Preventing Mould on Wood

Prevention is always easier than remediation. Here's how to reduce the risk of mould taking hold on timber surfaces in your home:

• Control humidity — use exhaust fans in bathrooms and kitchens, and consider a dehumidifier in high-risk areas
• Fix leaks promptly — don't let water sit against timber surfaces
• Improve ventilation — ensure sub-floor spaces, roof cavities, and enclosed rooms have adequate airflow
• Seal and maintain timber — painted or sealed wood is more resistant to moisture ingress
• Use a preventative mould spray — applying a mould inhibitor to at-risk surfaces can stop spores from taking hold in the first place

The Green Goo Approach

At Green Goo, we believe in tackling mould properly — not just masking it. Our eco-friendly mould removal products are formulated to kill mould at the source, without harsh chemicals that damage surfaces or harm your household. Whether you're dealing with a small patch on a window sill or a larger problem on decking or floorboards, we have a solution that works.

Explore our range of mould removers, concentrates, and refills — and stop mould from coming back for good.