Top Signs of Mould on Wood and What to Do About It

The main signs of mould on wood are fuzzy or powdery spots in black, green, white or grey, a musty smell, and discolouration that keeps coming back after wiping. Mould grows where wood stays damp, so you will usually find it near windows, behind furniture on outside walls, under sinks and in poorly ventilated rooms. If the wood itself feels soft, crumbles or has cracked into cubes, you may be dealing with rot rather than surface mould.

Spotting it early makes it far easier to deal with. Here is what to look for, how to tell mould from rot and stains, and what to do next.

What does mould on wood look like?

Mould on wood can take several forms. Look out for:

• Black or dark green speckles, often in clusters, on window frames, sills and the backs of wardrobes.
• White or grey fuzz that looks almost like dust but smears when touched.
• Blue-green or yellow patches, sometimes on untreated timber such as loft boards or garden furniture.
• Blotchy staining under varnish or paint, which can mean moisture has got in behind the finish.
• Spots that return within days or weeks of cleaning, a clear sign the damp source is still there.

What other signs point to mould you cannot see?

Mould is not always on display. It often grows on the hidden side of wood or in enclosed spaces. Be suspicious if you notice:

1. A persistent musty or earthy smell in a cupboard, wardrobe or room, even when surfaces look clean.
2. Condensation collecting regularly on windows and running onto wooden frames and sills.
3. Peeling paint or lifting varnish on skirting boards, doors or frames.
4. Warped or swollen wood, such as doors that start to stick or floorboards that cup.
5. Damp patches or tide marks on nearby walls or ceilings.
6. Musty-smelling clothes or shoes stored in wooden furniture.

How can you tell mould from rot or ordinary stains?

It is worth knowing the difference, because the solution is very different.

• Surface mould sits on top of the wood. It usually wipes away, and the wood underneath feels firm.
• Wet rot happens where timber stays wet for a long time. The wood becomes dark, soft and spongy, and may crumble when pressed.
• Dry rot is a more serious fungal decay. Signs include white, cotton-wool-like growth, fine rust-coloured dust, a strong mushroom smell and wood that shrinks and cracks into cube-shaped pieces.
• Water stains or tannin marks are flat and do not smear or grow. They may be a warning of past moisture but are not mould in themselves.

If you suspect any kind of rot, do not try to clean it away. Ask a qualified damp or timber specialist, or your landlord if you rent, to inspect it, because the structure may be affected.

Is mould on wood harmful to health?

NHS guidance explains that damp and mould can cause or worsen respiratory problems, allergies and asthma, and can affect the immune system. Some people are more at risk, including babies and young children, older people, anyone with an existing skin or breathing condition such as asthma, and those with a weakened immune system. It is best to deal with mould promptly and to keep vulnerable people away from the area while it is being cleaned. If you are worried about symptoms, speak to your GP or pharmacist.

Can you clean mould off wood yourself?

Small patches of surface mould caused by condensation can often be cleaned at home. Larger areas, mould caused by a leak, or mould that keeps returning should be looked at by a professional, and in rented homes reported to your landlord in writing.

For a small patch:

1. Protect yourself. Wear rubber gloves, goggles and a mask that covers your nose and mouth.
2. Ventilate. Open windows but keep internal doors closed so spores do not spread through the home.
3. Do not dry-brush. Brushing or vacuuming mould with a normal vacuum can release spores into the air.
4. Wipe gently with a cloth dampened in water and a mild detergent, or use a mould remover labelled as suitable for wood. Patch-test on a hidden area first, as some products can bleach or mark timber.
5. Dry the wood thoroughly with a clean cloth, and let it air-dry fully.
6. Bag the cloths in a plastic bag and dispose of them.

Bleach is not usually recommended on wood, because it can discolour timber and does not soak into it well. Whatever you use, follow the label and never mix bleach with ammonia or acidic cleaners.

How do you stop mould coming back on wood?

Cleaning removes the mould you can see, but controlling moisture is what keeps it away:

• Open windows or use extractor fans when cooking, showering and drying clothes.
• Wipe condensation off window frames and sills each morning.
• Leave a small gap between wooden furniture and outside walls so air can circulate.
• Keep the home consistently heated in colder months where possible.
• Fix leaks from pipes, gutters and roofs quickly.
• Seal or repaint bare timber in damp-prone areas once it is fully dry.

Want a thorough clean after dealing with damp?

Once the source of damp is fixed, a detailed clean can help reset the rooms that were affected. SN Cleaning Services offers a deep house cleaning service across London and Essex, with our own trained, insured and DBS-checked cleaners and professional products. Our cleaners focus on cleaning and are not a substitute for a damp survey, so where there are signs of rot or a structural problem, a specialist should come first. To see a price, click Get a quote and enter your postcode and email.