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Dry rot

When wood processed in buildings has a moisture level of more than 21% for a prolonged period of time, it is likely for fungi to grown on and in this moist food. The most prevalent wood harming fungus in the Netherlands is the Serpula lacrymans Both conifers and broad-leaved trees can be harmed by these fungi. The fungus can exist in beams and / or other wooden parts of the ground floor flooring. On or in wood outdoors, the dry rot is hardly ever found.

Appearance / Lifestyle
Wood affected by dry rot has a brownish discolouration. As the wood is affected further, it turns soft and loses its strength. An an advanced rotting stage, the wood is brown with deep parallel shrinkage cracks perpendicular to the fibre direction.

The fungal threads in the wood cannot be seen by the naked eye. These threads penetrate the wood to a very deep level. The cross-section of such threads is very small, just 0.0016 mm. At the surface of the wood the fungal threads are usually somewhat thicker, and sometimes visible in the form of white flakes. Fungal threads don’t just exist on wood, but also on stone or concrete floors of basements for instance, and in and on damp walls etc. Sometimes bundles of fungal thread are found with a diameter between 5 to 8 mm. These are called strands, and are white at first, and later turn grey.

In places where the fungal threads grow in the wood, substances are formed that degrade the cell walls. A portion of the wood is converted into carbon dioxide and water by the fungus. In this process, energy is released that is used for the growth of the fungus. Even dry wood can be affected, because dry rot is able to transport moisture from moist places using the fungal threads. After a while, fruiting bodies are formed on the wood or wall, consisting of compact tissue. The fruiting bodies are fairly flat, 1 to 3 cm, thick, brown with a white edge and vary in size from several centimetres to 1 meter. The fruiting bodies form the base for the spores that cause the species to spread. A fruiting body can form billions of spores. Large numbers of spores together look like rust-brown powder.

Dry rot develops the fastest in temperatures of 23 degrees Celsius. In 28 degrees C. or higher, the fungal threads die off. The spores however can withstand higher temperatures. At freezing temperatures the fungal growth comes to a halt, but the dry rot doesn’t die. After the frost period, the growth simply continues.

Prior to control measures, it is important to take all possible measures to prevent leakage, condensate, rising damp, resounding walls, water entry or high ground water levels. After the control measure, the wood should not be allowed to get moist again, because that would make it appealing for dry rot again.

The wood affected by fungus must first be removed. In addition, the adjacent, not visibly affected wood across a length of 1 meter must be removed and replaced, preferably with wood pre-emptively treated with a fungicide. Affected elements that cannot be removed must be treated with a curative agent, such as azaconazole or tributyltin phosphate. It isn’t simple to impregnate the wood with the necessary amounts of the substance in such a curative treatment. For that reason, the treatment must sometimes be carried out twice.

Walls that may contain fungal threads must also be treated. Loose stucco must be removed and the joints must be scraped out. Afterwards, the walls must be treated with the agent.

In case of serious deterioration due to dry rot, it is recommended to drill diagonal holes downward in the holes. The depth of the holes must be 2/3 of the wall thickness, 30 cm apart and 20 cm crosswise to each other. Afterwards, the drill holes are injected with the fungicide several times in a row. After drying, stucco can be applied to the wall. For a treatment against dry rot or other fungi, please contact the EWS.


EWS Pest control specialises in solving each and every pest problem in a professional and discrete manner. EWS’ service technicians are up to date with the applicable legislation and provide the best result based on the principles of Integrated Pest Management (IPM).

Would you like to speak to an advisor about pest control?

Jan-Willem van der Hoeven

Technical & Commercial Advisor
+31 6 82574349

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