How to Deal With Mouldy Wooden Pallets
20 Aug 2014
Any wooden pallet used to export goods will eventually become mouldy. It will be kept in a ship or aeroplane hold and open to the weather during loading and unloading. Within a couple of months, this will happen even to the best wood. The mould is often the most visible on the leg corners of pallets that often are not covered with plastic containment sheets.
All wooden pallets have to be heat-treated or chemically treated before entering Europe or the United States. But mould can never be totally avoided. Even heat-treated or chemically treated material can be attacked again when the circumstances are right.
However, mould only grows on the surface of a pallet; it does not attack the structural integrity of the wood. The problem is that it can contaminate and discolour the wood and, ultimately, the goods packed on the pallets. The mould can also contaminate a workplace, creating a health risk to employees. Finally, mould looks ugly on any surface.
There is no silver bullet to treat mould. Mould spores are present in the atmosphere and can land and grow on any suitable surface. This usually requires a wood surface with more than 20 per cent moisture content and temperatures of between 15 and 35 degrees Celsius. Many moulds are able to grow at much lower temperatures as long as they are above freezing point.
The mould growth comes in the form of tentacles, called mycelia, which spread over the wood and produce more spores at the same time. This growth can spoil food stuffs and spread diseases. It can irritate existing asthma conditions and in the worst cases can be a carcinogen.
The mould can be controlled by reducing wood’s moisture content to below 20 per cent and maintaining it at that level. In addition, the atmospheric spore density in the working area occupied by wooden pallets should be controlled.
A simple 2:1 mixture of water and household bleach can kill existing mould and new mould spores but will not stop them from reoccurring. So it is important that all storage areas for pallets should be well ventilated, dry and free of any excess piles of wooden materials or other debris that could become a breeding centre for mould spores.
All wooden pallets should be dried to a surface moisture content of 20 per cent and a total moisture content of a maximum of 25 per cent before being used for shipping goods. This can be achieved by a simple fan-drying system. Arrange the pallets well spaced apart in a shed or other dry, indoor environment, and switch on a fan to direct airflow through the batch.
The airflow allows the moisture to wick from the surface and dries the wood. It’s a good idea to reverse the airflow from the fans so that all surfaces of the wood are treated. This process will take between 10 and 21 days.
The process will limit mould growth on the pallets. It should be combined with a mild chemical treatment of the wood to prevent future mould growth. However, it is important to realise that if the pallets are left open to the weather during shipping, the mould growth will resume anyway.