Is Fungus-Covered Firewood Safe to Burn?

Firewood can sometimes develop fungus, mould or white patches when it has been stored in damp, poorly ventilated conditions. In many cases, minor surface fungus on otherwise dry firewood does not mean the wood is completely ruined. However, mouldy, wet or rotten firewood should be treated with caution, especially if it is being burned indoors.

The safest approach is simple: only burn dry, well-seasoned firewood that is solid, clean enough to handle and has been stored properly. If the wood is wet, soft, rotten, musty or heavily covered in mould, it is better not to burn it inside a fireplace or wood heater.

Turtle Nursery supplies firewood, kindling and landscape supply products for Sydney homeowners, landscapers and trades, with pickup and delivery options available.

What Causes Fungus to Grow on Firewood?

Fungus grows on firewood when moisture and poor airflow create the right conditions.

This can happen when firewood is:

• Stored directly on wet ground
• Left uncovered in rain
• Covered too tightly with plastic
• Packed too closely together
• Stored in a dark, damp area
• Not properly seasoned before storage
• Exposed to humid weather for long periods

Firewood is a natural timber product, so some surface changes can happen during storage. The important question is whether the wood is still dry, solid and suitable to burn.

Is Fungus on Firewood Always a Problem?

Not always.

A small amount of dry surface fungus on firewood that is otherwise seasoned and solid may not mean the wood is unusable. Outdoor-stored timber can sometimes show light white marks, staining or surface growth.

The bigger concern is when the firewood is damp, soft, rotten or heavily mouldy. That usually means the wood has been stored badly or has absorbed too much moisture.

If it smells musty, feels wet or crumbles easily, avoid burning it indoors.

When Should You Not Burn Firewood?

Do not burn firewood if it is:

• Wet or green
• Rotten or spongy
• Heavily covered in mould
• Treated, painted or stained
• Made from construction waste
• Chemically treated timber
• Producing a strong musty smell
• Difficult to light because of moisture

Poor-quality firewood can produce more smoke, burn inefficiently and create more mess inside the fireplace or heater.

Health Risks of Burning Mouldy Firewood

Burning mouldy firewood indoors is not ideal, especially for people with asthma, allergies or respiratory sensitivity.

The main issue is not only the burning itself. Handling mouldy wood, carrying it indoors and storing it near living areas can spread spores and musty material.

For indoor fireplaces and wood heaters, it is better to use dry, seasoned firewood that has been stored in a well-ventilated area.

What Is the White Mould on Firewood?

White mould or fungus on firewood usually appears because the timber has been exposed to moisture.

It may look like:

• White powdery patches
• Light fuzzy growth
• Pale staining
• Small fungal marks on bark
• Surface growth on split faces

If the firewood underneath is dry and solid, the issue may be minor. If the wood is damp, soft or smells musty, it is better not to use it indoors.

Is Black Mould on Firewood Dangerous?

Black mould or dark fungal growth should be treated more seriously, especially if the wood is damp or heavily affected.

Avoid bringing heavily mouldy timber inside. Even if the wood eventually burns, handling and storing mouldy firewood indoors can be unpleasant and may irritate sensitive people.

If in doubt, keep it outside and choose cleaner, drier firewood for indoor use.

Is Wood Ruined If It Gets Mouldy?

Not always.

Firewood with minor surface mould may still dry out if it is stacked correctly in a sunny, well-ventilated area. However, if the wood has started to rot, soften or break down, it is no longer good-quality firewood.

A practical test is:

If the firewood is dry, solid and burns well, it may still be usable. If it is wet, soft, rotten or heavily mouldy, do not rely on it for indoor heating.

How to Tell If Firewood Is Still Usable

Usable firewood should usually be:

• Dry to the touch
• Firm and solid
• Split rather than whole and wet
• Easy to light with kindling
• Free from strong musty odours
• Stored off the ground
• Not heavily mouldy or rotten

Dry firewood often sounds sharper when knocked together. Wet firewood tends to feel heavy, dull and harder to light.

For more help, read Turtle Nursery’s guide on seasoned firewood vs green firewood.

What Kills Mould on Firewood?

For firewood, the best solution is usually not chemical treatment. It is better to improve storage conditions.

Move the firewood to a dry, sunny and well-ventilated area. Stack it off the ground and allow air to move through the pile. Avoid spraying chemicals on firewood that may later be burned.

If the timber is badly mouldy or rotten, it may not be worth saving for indoor firewood use.

How to Store Firewood to Prevent Fungus

Good storage is the best way to prevent fungus.

To store firewood properly:

1. Stack it off the ground.
2. Keep the sides open for airflow.
3. Cover the top, not the whole stack.
4. Avoid wrapping firewood tightly in plastic.
5. Keep it away from damp walls.
6. Store it in a sunny, ventilated spot if possible.
7. Bring only a small amount indoors at a time.

The aim is to keep rain off while allowing moisture to escape.

For more detail, see Turtle Nursery’s guide on how to store firewood properly in winter.

What Kind of Wood Should Not Be Burned?

Avoid burning:

• Treated pine
• Painted timber
• Stained timber
• MDF or particleboard
• Construction waste
• Driftwood
• Rotten wood
• Wet green timber
• Heavily mouldy timber

Firewood should be natural, dry and suitable for heating.

You can browse Turtle Nursery’s firewood supplies for firewood and kindling options.

Summary

Minor surface fungus on firewood does not always mean the wood is ruined, but mouldy, wet, soft or rotten firewood should not be burned indoors. The safest firewood is dry, seasoned, solid and stored with good airflow. To prevent fungus, stack firewood off the ground, cover only the top and keep the sides open so moisture can escape.

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