How to get rid of mould from a wooden shed?
- 1. Why is mould in a garden shed a serious problem?
- 2. Where does mould come from? Main causes
- 3. How to recognise mould?
- 4. How to effectively remove mould from a wooden garden shed step by step?
- 5. How to prevent mould from returning to your garden shed?
- 6. Bertsch Holzbau products – when prevention starts with quality
- 7. Summary
Wooden garden sheds are a charming and functional element of many gardens. Unfortunately, mould can be an inherent problem with their use. It is not only an aesthetic defect, but also a real threat to the health of users and the durability of the structure. In this guide, you will learn how to effectively and safely remove mould from your garden shed and how to prevent it from returning.
Why is mould in a garden shed a serious problem?
Mould in a garden shed is not just a matter of aesthetics – it is primarily a health and structural problem. Mould fungi thrive in conditions of high humidity and poor ventilation, especially when the wood has not been properly protected.
At first, it may look inconspicuous – as a grey or black coating on the wall. However, over time it can lead to:
- weakening of the wood structure, causing cracks, deformation and a reduction in the load-bearing capacity of the structure,
- an unpleasant musty smell that lingers inside and permeates stored items,
- negative health effects, especially in children, allergy sufferers and people with respiratory diseases (e.g. asthma).
What’s worse, mould has the ability to spread quickly – not only within the structure, but also to tools, garden fabrics, books, boxes with soil and even living plants. The longer it is ignored, the more difficult it is to remove and the more difficult it is to restore the shed to a safe condition.
BHB expert tip:
Fungus-infected surfaces may look harmless, but mould spores are invisible to the naked eye – so don’t put off cleaning infected areas.
Where does mould come from? Main causes
Mould does not appear without a reason – its growth is always the result of favourable environmental conditions and construction or usage errors. Understanding the sources of the problem is the first step towards effective prevention and elimination.
Here are the most common causes of mould in wooden garden structures:
1. Lack of ventilation
A closed room without windows or ventilation grilles is an ideal environment for moisture. Water vapour from the soil, tools or plants has nowhere to escape and settles on the walls, where mould fungi develop over time.
2. Poor location of the shed
A shed located in a permanently shaded area or directly on damp ground absorbs moisture from the environment. Water drawn up by capillary action from the foundation can penetrate the structure, which is particularly dangerous in the case of uninsulated wood.
3. Lack of impregnation and wood protection
Raw, unimpregnated wood acts like a sponge, absorbing moisture from the air and precipitation. Without a protective layer, fungi have ideal conditions for growth. Lack of regular maintenance only exacerbates the situation. Read our expert article “How to stop condensation and moisture in a shed” .
4. Structural leaks
A damaged roof, poorly fitted windows or gaps in the floor are ‘weak points’ through which water can get inside. It is there, in the shady corners, that the first signs of mould usually appear.
Conclusion: Even the best-built garden shed can become damp if it is not properly positioned, protected and ventilated. Therefore, the design and use of a shed requires informed decisions – especially in the humid climate of Western Europe.
How to recognise mould?
Mould in a garden shed can go unnoticed for a long time, especially if the structure is not used regularly or has not been properly finished on the inside. It is therefore important to know the first signs of the problem and to regularly check the most vulnerable areas.
Symptoms that should raise alarm bells:
- Black, green or white coating – usually appears on the lower parts of walls, where the wood meets the foundation, in corners or around leaky windows and doors. It may resemble powder or a thin layer of cotton wool, becoming more visible and extensive over time.
- A musty smell – this is one of the first signs. An unpleasant, earthy odour, particularly noticeable when entering the house, indicates the growth of fungi in a closed, damp environment.
- Dull wood – if the surface was previously smooth and varnished, the presence of mould can lead to flaking of the coating, paint peeling or local discolouration of the material. The wood may become rough and dull.
Important!
Not every dark spot is necessarily mould – sometimes it can be a mineral deposit or dirt. Try wiping the area with a damp cloth – if the coating does not disappear or smears, you are probably dealing with fungus.
How to effectively remove mould from a wooden garden shed step by step?
To get rid of mould once and for all, it is worth following the appropriate procedure. Here is a proven plan of action:
Step 1. Put on personal protective equipment
Mould produces spores that float in the air and can be inhaled, causing irritation, allergic reactions and, in sensitive individuals, respiratory problems. Therefore, before you start work, put on rubber or nitrile gloves, use a dust filter mask (minimum FFP2), protect your eyes with safety goggles, and wear clothing that can be washed immediately.
Step 2. Remove all items from the shed
Do not leave anything inside – spores can be found on toolboxes, rugs, buckets and textiles. Take the items outside and leave them in the sun to air out.
Tip: if any of the items show visible signs of mould, clean them and, if this does not help, consider disposing of them.
Step 3. Remove the mould mechanically
Before using chemicals, remove the mould physically:
- use a stiff brush,
- you can use a scraper if the coating is thick or dried,
- work thoroughly – do not skip corners, lower parts of walls or spaces near windows.
Removing mould mechanically limits its spread and improves the effectiveness of further cleaning.
Step 4. Apply a fungicide
Once the wood surface has been cleaned of visible mould:
- use a product based on hydrogen peroxide, isopropyl alcohol or a dedicated wood preparation,
- avoid strong chlorine-based chemicals – they can damage the structure of the wood,
- spread the product evenly with a brush, sponge or sprayer,
- and leave to dry according to the manufacturer’s instructions.
Step 5. Intensive ventilation – min. 24 hours
After cleaning, leave the shed open for at least 24 hours. This is best done on a dry, sunny day – UV rays and heat help remove moisture. You can help the process along by using fans or a heater. Remember that moisture is mould’s best friend. The faster the wood dries, the lower the risk of it coming back.
Step 6. Protect the wood with a preservative
This is the most important preventive measure:
- use a protective preservative with fungicidal properties,
- choose oil, resin or wax-based products that will not only protect but also nourish the wood,
- apply two coats – the second after the first has completely dried.
BHB expert tip:
Impregnation is not an expense, but an investment – a well-protected garden shed will serve you for years, even in the changing climate of Germany or the United Kingdom.
How to prevent mould from returning to your garden shed?
Proper prevention is the key to preventing mould from returning, even after it has been successfully removed. Wood, especially when used outdoors, works and absorbs moisture from the environment. If we do not ensure the right conditions inside the shed, mould will reappear very quickly.
Below are some steps you can take to prevent mould from returning:
- Ensure air circulation – ventilation is the most effective way to prevent water vapour condensation. Install ventilation grilles on opposite sides of the shed or leave micro-gaps in the roof or floor to allow natural air flow.
- Use moisture absorbers – especially in autumn and winter or in houses used occasionally. A simple granule absorber can reduce moisture levels by up to 20-30% and prevent mould from forming on stored items.
- Apply impregnation every 1-2 years – choose products containing biocides, which not only protect against moisture but also protect the wood from the growth of fungi and microorganisms.
- Avoid storing wet items – even if the shed is well ventilated, a few garden cushions after rain or a damp garden hose are enough to significantly increase the moisture level. Always allow items to dry outside before storing them in the shed. To getting more information on how to prevent garden shed from water check this article.
BHB expert tip:
The best prevention is a well-designed structure – with adequate ventilation and the right impregnation. At BHB, we use naturally dried wood and recommend regular inspections – especially after winter.
Bertsch Holzbau products – when prevention starts with quality
At BHB, we believe that the best protection against mould starts at the production stage. That is why all our wooden structures – including the popular ZULUNA series – are made of certified Scandinavian spruce, whose slow growth in a cool climate ensures dense grain and exceptional strength. Our wood is resistant to weather conditions and pests, making it suitable for year-round use.
Additionally:
- the cabins are designed for optimal air circulation – e.g. thanks to the well-thought-out design of the roofs and floors and the option of adding ventilation systems,
- we offer construction variants with additional surface protection – e.g. oil, glaze or protective varnish,
- we advise our customers on how to regularly maintain and inspect the structure to avoid problems with moisture and mould.
At ZULUNA, we place particular emphasis on functionality and durability – that is why our houses are prepared for use in changing climatic conditions as standard, so no location is too challenging for them – they are ideal for both Germany and the United Kingdom.
BHB expert statement:
Mould most often appears where details have been overlooked – poorly impregnated roofs, lack of foundation details, lack of ventilation. We take these details into account at the design stage, which is why a BHB cabin is not only aesthetically pleasing, but also peaceful and comfortable to use for many years.
Summary
Mould in a wooden garden house is a problem that requires a quick and effective response. With the right measures and treatments, you can not only get rid of existing mould, but also effectively prevent it from returning. Remember – prevention starts with good quality wood and proper care. Trust the proven solutions from BHB – and enjoy a healthy, dry and friendly garden house all year round.
